RICE-FISH CULTURE
in
CHINA
E D I T E D
B Y
Kenneth T. M a c K a y
INTERNATIONAL
DEVELOPMENT RESEARCH CENTRE
O t t a w a • Cairo • Dakar • Johannesburg • Montevideo
N a i r o b i • New Delhi • S i n g a p o r e
Published by the International Development Research Centre
PO Box 8500, Ottawa, ON, Canada K1G 3H9
June 1995
MacKay, K.T.
Chinese Academy of Agricultural Sciences, Beijing CN
Chinese Academy of Fisheries Sciences, Wuxi CN
Rice-fish culture in China. Ottawa, ON, IDRC, 1995. 276 p.: ill.
/Rice/, /plant production/, /fish production/, /mixed farming/, /cultivation
systems/, /China/ — /appropriate technology/, /ecology/, /economic
aspects/, /on-farm research/, /case studies/, /conference reports/, references.
UDC: 633.18:639.2(510)
ISBN: 0-88936-776-0
A microfiche edition is available.
Material contained in this report is produced as submitted to IDRC Books.
Unless otherwise stated, copyright for material in this report is held by the
authors. Mention of a proprietary name does not constitute endorsement of
the product and is given only for information.
Contents
Preface
vii
Introduction Wang Hongxi
ix
Part I: Review and Outlook
Rice-Fish Culture in China: The Past, Present, and Future
Cai Renkui, Ni Dashu, and Wang Jianguo
3
Rice-Fish Culture in China: Present and Future
Chen Defu and Shui Maoxing
15
Scientific and Technological Development of Rice-Fish Culture in China
Zhang Rongquan
23
Development of Rice-Fish Farming in Guizhou Province
Shi Songfa
31
Reforming Rice-Fish Culture Technology in the Wuling Mountains of Eastern
Guizhou Province
Chen Guangcheng
37
The Development of Rice-Fish Farming in Chongqing City
Xu Shunzhi
43
Development of Rice-Fish Farming in Jiangsu Province
Xu Guozhen
49
Rice-Fish Culture and its Macrodevelopment in Ecological Agriculture
Yang Jintong
55
Value of the Rice-Fish Production in High-Yielding Areas of Yuyao City,
Zhejiang Province
Cao Zenghao
63
Developing Rice-Fish Culture in Shallow Waters of Lakes
Wan Qianlin, Li Kangmin, Li Peizhen, Gu Huiying, and Zhou Xin
67
iii
iv
RICE-FISH CULTURE IN CHINA
Part II: Patterns and Technology
Different Methods of Rice-Fish Farming
Nie Dashu and Wang Jianguo
77
New Techniques for Raising Fish in Flooded Ricefields
Wan Banghuai and Zhang Qianlong
85
Methods of Rice-Fish Culture and their Ecological Efficiency
Wu Langhu
91
Ridge-Cultured Rice Integrated with Fish Farming in Trenches, Anhui Province
Yan Dejuan, Jiang Ping, Zhu Wenliang, Zhang Chuanlu,
and Wang Yingduo
97
Development of Rice-Fish Culture with Fish Pits
Feng Kaimao
103
Techniques Adopted in the Rice-Azolla-Fish System with Ridge Culture
Yang Guangli, Xiao Qingyuan, and He Tiecheng
107
Semisubmerged Cropping in Rice-Fish Culture in Jiangxi Province
Liu Kaishu, Zhang Ningzhen, Zeng Heng, Shi Guoan,
and Wu Haixiang
117
Rice-Azolla-Fish Symbiosis
Wang Zaide, Wang Pu, and Jie Zengshun
125
Economic and Ecological Benefits of Rice-Fish Culture
Li Xieping, Wu Huaixun, and Zhang Yongtai
129
Cultivating Different Breeds of Fish in Ricefields
Wang Banghuai and Zhang Qianlong
139
Rice-Fish Culture in Ricefield Ditchponds
Luo Guang-Ang
147
Techniques for Rice-Catfish Culture in Zero-Tillage Ricefields
Chen Huarong
153
Demonstration of High-Yield Fish Farming in Ricefields
Cai Guanghui, Ying Yuguang, Wu Baogan, He Zhangxiong,
and Lai Shengyong
163
Rice-Azolla-Fish in Ricefields
Chen Defu, Ying Hanquing, and Shui Maoxing
169
CONTENTS
V
Part III: Interactions
Material Cycles and Economic Returns in a Rice-Fish Ecosystem
Ni Dashu and Wang Jianguo
177
Fish Culture in Ricefields: Rice-Fish Symbiosis
Xiao Fan
183
Ecological Effects of Rice-Fish Culture
Pan Yinhe
189
Ecological Mechanisms for Increasing Rice and Fish Production
Pan Shugen, Huang Zhechun, and Zheng Jicheng
195
Rice-Azolla-Fish Cropping System
Liu Chung Chu
201
Effect of Fish on the Growth and Development of Rice
Li Duanfu, Wu Neng, and Zhou Tisansheng
209
The Role of Fish in Controlling Mosquitoes in Ricefields
Wu Neng, Liao Guohou, Lou Yulin, and Zhong Gemei
..
213
A Comparative Study of the Ability of Fish to Catch Mosquito Larva
Wang Jianguo and Ni Dashu
217
Ability of Fish to Control Rice Diseases, Pests, and Weeds
Yu Shui Yan, Wu Wen Shang, Wei Hai Fu, Ke Dao An,
Xu Jian Rong, and Wu Quing Zhai
223
Distribution and Residue of Methamidophos in a Rice-Azolla-Fish Ecosystem
Xu Yinliang, Xu Yong, and Chen Defu
229
Residue and Application of Fenitrothion in a Rice-Fish Culture System
Lou Genlin, Zhang Zhongjun, Wu Gan, Gao Jin, Shen Yuejuan,
Xie Zewan, and Deng Hongbing
237
Part IV: Economic Effects
Economic Analysis of Rice-Fish Culture
Lin Xuegui, Zhang Linxiu, and He Guiting
247
Economic Research on Rice-Fish Farming
Jiang Ci Mao and Dai Ge
253
Ecology and Economics of Rice-Fish Culture
Quing Daozhu and Gao Jusheng
259
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Preface
A National Rice-Fish Farming Systems Symposium was held in China at the
Freshwater Fisheries Research Centre of the Chinese Academy of Fisheries
Sciences in Wuxi, Jiangsu Province, 4-8 October 1988. The symposium was
cosponsored by the Chinese Academy of Agricultural Sciences (CAAS) and the
Chinese Academy of Fisheries Sciences (CAPS). Funding was supplied by IDRC
through its project Farming Systems (China) (3-P-87-0237).
Researchers from the major rice-producing areas of China presented papers at this
interdisciplinary symposium. The proceedings of this symposium were originally
published in Chinese by the Agriculture Publishing House (Beijing). To share this
valuable information with researchers and development workers outside China, the
proceedings were translated into English. The initial translation was done either by
the researchers themselves or by translators with the Agricultural Publishing
House. Initial English editing was carried out by Regina Morales, Manila,
Philippines. Final technical editing and preparation of the camera-ready copy was
undertaken by Michael Graham, MG Science Editing, Writing, and Publishing,
Kemptville, Ontario, Canada. In some cases, two or more papers have been
combined to remove redundancy.
Kenneth T MacKay
Winsloe
Prince Edward Island
Canada
vii
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Introduction
This symposium on rice-fish farming in China brought together 55 experts and
scholars from the Academia Sinica, the Departments of Agriculture and
Hydraulics, the Institutes of Aquacultural Research and Education, and the
Administration Bureaus. In addition, there were representatives from the
International Development Research Centre, Canada, the Network for Aquaculture
Centres in Asia (NACA), Thailand, the Freshwater Aquaculture Center, Central
Luzon State University, Philippines, and the International Center for Living
Aquatic Resources Management.
China has had a long history of rice-fish farming. As rural areas have been
industrialized in recent years, rice-fish farming has gained attention because it is
an organic method that combines rice and fish production while maximizing labour
and ricefield resources. The Chinese Academy of Agricultural Sciences and the
Chinese Aquacultural Research Institute organized this symposium, with financial
assistance from the International Development Research Centre, to synthesize the
rich experiences and skills of Chinese farmers and to improve rice-fish farming as
a way to increase food production in Southeast Asia and in other parts of the
world.
Rice has always been the number one grain crop in China in terms of both area and
yield. During the 1950s, the tradition of rice-fish farming developed substantially
but the benefits were not significant. Fish harvests were poor because the method
was based only on traditional experiences and technical difficulties were
encountered. However, rice-fish farming developed rapidly and by 1988,
800000 ha were being harvested with a average yield of 133 kg/ha. In some areas,
yields exceeded 3750 kg/ha and many farmers harvested 15000 kg of rice and
1500 kg of fish per hectare. The incomes of these farmers increased considerably.
The techniques of rice-fish farming improved markedly as additional skill and
experience were acquired.
In 1972, Ni Dashu, of Academia Sinica' s Institute of Hydrobiology, initiated
experiments to increase fish production from rice-fish culture. These experiments
established the theory for rice-fish integration, which guided the research work of
Chinese scientists during the 1980s. Research was focused on the common needs
of fish and rice for water, light, and nutrition under local conditions. Many new
techniques were developed to suit various locations: ridge and ditch systems;
semidry land; ditch manure pits; ditches with floating water; and
rice-duckweed-fish systems. These new methods enriched and further developed
the theory of rice-fish integration.
ix
x
RICE-FISH CULTURE IN CHINA
In 1984, the State Economic Commission arranged a project for the extension of
these new techniques. The Fisheries Bureau, under the Ministry of Agriculture,
Animal Husbandry and Fisheries, ordered a technical coordination group to carry
out the work in Sichuan and 17 provinces, municipalities, and autonomous regions.
After 3 years, the new techniques were widely adopted and produced economic,
social, and ecological benefits that contributed to the large-scale adoption of
rice-fish farming in China.
Rice-fish fanning is no longer limited to the household economy and to production
for personal or family consumption. It is now part of farmland improvement, soil
improvement, and environmental protection. Rice-fish farming has increased the
productivity of ricefields and is fast becoming an important part of the commodity
economy. It has also played a significant role in reforming the structure of rural
industries.
Wang Hongxi
Deputy Director
Chinese Academy of Fishery Sciences
Part I:
Review and Outlook
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Rice-Fish Culture in China: The Past, Present, and Future1
Cai Renkui,2 Ni Dashu,3 and Wang Jianguo3
The combination of rice and fish has a long history in China. The practice of
rice-fish farming may have evolved from pond culture. The canon for fish culture
written by Fan Li about 400 BC states:
... dig six mu of land into a pond... put 2 000 fry into the pond .... sell the
rest in the market.
In a good year with ample rainfall and moderate weather, 2 000 carp fry could
produce numerous eggs. Some wise farmers may have placed excess fry in their
ricefields. The fish in the ricefields may have grown better than those in the ponds,
and the practice of raising fish in ricefields was born. There are no records of when
the practice started, but this seems to be a logical explanation of how rice-fish
farming began in China.
The archeological and written records do suggests the rice-fish culture is almost
2000 years old. In 1964-1965, tombs of the mid-Eastern Han Dynasty
(25-220 AD) were excavated in the suburbs of Hanzhong County, Shanxi
Province. Two clay models were unearthed: a model of a pond and a model of a
ricefield. The pond model contained 15 miniature pieces (6 common carp,
1 soft-shell turtle, 3 frogs, and 5 water chestnuts). In 1977, a stone carving of a
pond and ricefield model was discovered in the brick tomb of the Eastern Han
Dynasty in Emei County, Sichuan Province. Half the stone was carved into a pond
with frogs, fish, and ducks. The other half was carved into a ricefield with an inlet
and outlet, two farmers toiling on one side, and two heaps of manure on the other.
In 1978, four mid-Han Dynasty tombs with 200 relics were excavated in Mian
County, Shanxi Province. One of the intact relics was a ricefield model containing
18 pottery miniatures of aquatic plants and animals. In it were sculptured frogs,
eels, spiral shells, crucian carp, grass carp, common carp, and turtles. Another of
a winter ricefield showed farmland with a reservoir that also contained these fish.
1
This paper is a combination of two papers: The History of Rice-Fish
Culture in China by Cai Renkui and The Past, Present, and Future of Rice-Fish
Farming in China by Ni Dashu and Wang Jianguo.
2
Freshwater Fisheries Research Centre, Chinese Academy of Fisheries
Science, Wuxi, Jiangsu Province.
3
Institute of Hydrobiology, Academia Sinica, Wuhan, Hubei Province.
RICE-FISH CULTURE IN CHINA
These relics suggest that at least 1700 years ago, rice-fish culture was practiced
in the vicinity of Hanzhong and Mian Counties in Shanxi Province, and in Emei
County in Sichuan Province. The fish species stocked in the ricefields were
common carp (Cyprinus carpio), crucian carp (Carassius auratus), grass carp
(Ctenopharyngodon idellus), and silver carp (Hypophthalmichthys molitrix). The
bamboo fish trap and sluice gate that were installed at the inlet and outlet indicate
that a primitive model of rice-fish culture existed at that time.
The earliest written record of rice-fish culture is from Recipes for Four Seasons,
which was written in the Wei Dynasty (220-265 AD):
A small fish with yellow scales and a red tail, grown in the ricefields of Pi
County northeast of Chendu, Sichuan Province can be used for making
sauce.
The small fish with yellow scales and a red tail could be common carp. This
indicates that common carp may have been grown in ricefields in Pi County. This
record coincides with excavated relics. An alternate view4 is that the fish referred
to is a type of small carp that "came from rice paddies" but was not necessarily
raised in the ricefields. It is possible that, instead of being raised by rice growers,
the fish was washed into ricefields during the rainy season through flooded
waterways.
Rice-fish culture probably continued to develop. The next written record is found
during the latter part of the Tang Dynasty. Liu Xun (about 889-904 AD), wrote
in Wonders in Southern China:
InXin, Long, and other prefectures, land on the hillside is wasted but the
flat areas near the houses are hoed into fields. When spring rains come,
water collects in the fields around the houses. Grass carp fingerlings are
then released into the flooded fields. One or two years later, when the fish
are grown, the grass roots in the plots are all eaten. This method not only
fertilizes the fields, but produces fish as well. Then, rice can be planted
without weeds. This is the best way to farm.
The districts of Xin and Long are now in the vicinity of Xinxing and Luoding
Counties in Guangdong Province. This means that rotational rice-fish farming was
practiced there over 1000 years ago. The chronicle of Shunde County,
Guangdong, from the Ming Dynasty (about 1573) states that:
The periphery of a land was trenched as a plot, called the field base. ...In
the plot, a pond was dug to rear fish. During the dry season, rice seedlings
were transplanted to the plot. The area might be several hectares.
4
The first view was expressed in the paper by Cai Renkui; whereas, the
alternate view was expressed by in the paper by Ni Dashu and Wang Jianguo.
REVIEW AND OUTLOOK
5
According to this chronicle, the area for rice-fish culture was expanded in
Guangdong 400 years ago.
Formal research appears to have started in the 20th century. In 1935, a rice-fish
culture experiment was conducted in Songjian, Jiangsu Province. The species
stocked were black carp (Mylopharyngodon piceus), grass carp, silver carp,
bighead carp (Aristichthys nobilis), and common carp. During the rice-growing
period, the weight of the silver carp increased 50-fold and the weight of common
carp increased 20-fold. After 2 years, 20000 fry hatched and were distributed to
farmers for culture in rice paddies. Scientists provided technical assistance.
After the founding of the People's Republic of China in 1949, rice-fish culture
developed quickly. In 1954, the fourth National Aquaculture Meeting proposed the
development of rice-fish culture across the country. By 1959, the area of rice-fish
culture had been expanded to 666000 ha.
From early 1960s to the mid!970s, several factors, including the intensification of
rice production and the large-scale application of chemical insecticides, impeded
the development of rice-fish culture.5 For example, in Guangdong Province the
area of rice-fish culture dropped from 33 333 ha in the early 1950s to 320 ha in the
mid 1970s, and in Hunan Province the area dropped from 232000 ha in 1958 to
5 333 ha in 1978.
Rice-Fish Fanning in China Today
During the late 1970s, there were changes in rice production. Improved modern
varieties of rice and less toxic chemicals were used and there were changes in the
units of production. The production-contract system was implemented in rural areas
starting in 1978 and this allowed individual families to become the main units of
production. In addition, there was a rapid development of aquaculture, which
required the production of a large amount of fry and fingerlings. This demand was
partly met by fmgerling production in ricefields. Research and supporting policy
and development activities have also encouraged the expansion of rice-fish
production.
The research established an optimum ecological system to increase rice production,
economize labour, and maximize economic returns. This lead to the evolution of
a theory of rice-fish mutualism that has provided the theoretical basis for rice-fish
culture. The practice has now spread to all rice-growing areas in China through the
adaptation of rice-fish techniques that are suitable to local agroecological
conditions.
5
The years 1965-1975 also coincided with the cultural revolution. During
this period, the raising of fish was considered a bourgeois way of making money
and was officially discouraged. In addition, there were severe dislocations of
research and extension during this period.
6
RICE-FISH CULTURE IN CHINA
A number of regional and national meetings focused attention on rice-fish culture
and advanced its development. In 1983, a workshop on Fish Farming for
Eradicating Mosquitoes was held in Xinxiang, Henan Province, to exchange
information on eradicating mosquitoes by rearing fish in ricefields. The First
National Ricefield Fish Culture Seminar was held on 11-15 August 1983 at
Wenjian County, Sichuan Province, under the auspices of the Ministry of
Agriculture, Animal Husbandry and Fisheries (now the Ministry of Agriculture).
The seminar established a large coordination group for Eastern China to popularize
rice-fish farming techniques.
The potential and actual production in Eastern China is summarized in Table 1.
There are 9 million ha of ricefields in Eastern China. This accounts for one-third
of the country's total rice area, and 45% of it is suitable for raising fish. Before
1982, rice-fish farming was concentrated in the mountainous areas of Jiangxi,
Fujian, and Anhui and covered only 26 000 ha. The area was expanded to include
the plains and, by 1986, 138 000 ha were in production and yielded an average of
183 kg of fish per hectare.
In 1983, a key research project on the economics of aquatic resources in China
included a subproject on economic problems related to rice-fish culture. The
scientists, who thoroughly studied the economic benefits of rice-fish culture,
received the Second Science and Technology Progress Award from the Agriculture
Ministry in 1988.
In 1984, the Ministry of Agriculture, Animal Husbandry and Fisheries (MAAHF),
organized a project to popularize the technique of raising fish in ricefields in
Sichuan, Beijing, Hebei, Shanghai, Jiangsu, Anhui, Zhejiang, Jiangxi, Fujian,
Henan, Hubei, Hunan, Guangdong, Guangxi, Shaanxi, Guizhou, and Yunnan. To
promote the project, a technical group of six researchers was formed to provide
guidance.6 The members of the group were: Jiang Cimao of the Aquatic Products
Bureau of Sichuan Province, Ni Dashu of the Institute of Hydrobiology of the
China Academy of Sciences, Yin Pizhen of the Aquatic Products Institute of
Jiangxi Province, Yang Yongshuan of the Aquatic Products Bureau of Hubei
Province, Yang Jintong of the Aquatic Products Bureau of Hunan Province and Xu
Xushi of the Bureau of Agriculture, Animal Husbandry and Fisheries of Zhongging
City. The project sought to popularize the practice on a large scale. Initial
achievements won the project a first-class award for technological progress from
the MAAHF in 1986.
In 1985, 17 institutes were involved in another key research project called,
"Ricefields as Fish Nurseries and Fish Grow-out Systems." This project, under the
auspices of the National Aquatic Products Bureau, aimed to rear hybrids of
common carp, tilapia, and crucian carp (Carassius carassius) in ricefields and to
nurture grass carp fingerlings in ricefields. Each province was requested to extend
rice-fish culture in a 200 ha demonstration area. The target yield was 225-625 kg
6
A number of the researchers in this group were present at this workshop.
7
REVIEW AND OUTLOOK
Table 1. Rice-fish culture in Eastern China in 1985 and 1986.
.
Suitable
Area of
for
Province or Ricefields Rice-Fish
(Itfha)
Municipality (Itfha)
Area Used for
Rice-Fish
(1Q3ha)
1985
Fish Production
(tonnes)
Production
(k/ha)
1986
1985
1986
1985
1986
Jiangxi
2067
1400
52
47
9360
8815
180
188
Fujian
1040
400
22
28
2915
4265
131
150
Anhui
1667
667
23
34
6500
6630
285
195
Zhejiang
1333
667
21
19
3050
2810
149
150
Jiangsu
2400
667
11
10
2585
2760
237
267
Shanghai
200
200
0.8
0.2
1
11
150
450
Shandong
66
0.7
0.4
3
0.5
153
-
Total/
Average
8773
183.6
183
13
4014
131
138
24414 25292
of fish per hectare. The total demonstration area of rice-fish culture in the eight
provinces south of the Yangtze River was 1600 ha. The project sought to promote
the extension of rice-fish culture in the country to cover a total area of 800000 ha.
There was also an increase in rice-fish culture in Northern China. In 1985, the
Aquatic Products Section of the Water Resources Committee of the city of Urumqi
in the Xinjiang Uygur Autonomous region in Northwest China, carried out an
experiment on rearing fish varieties in ricefields in the northern suburbs of
Urumqi. They put 1977 fingerlings in two batches (10 and 2-3 cm in length) into
a 0.4-ha experimental field. After 68 and 87 days, they harvested 174 kg of fish
per hectare. The largest fish weighed 0.25 kg and the average weight was 0.11 kg.
Rice output was 9292.5 kg/ha, 18% more than in 1983. Net profit was
CNY1916/ha.
From 1984 to 1985, the Rice Institute of the Agricultural Reclamation Academy
in Heilongjiang Province, Northeast China, conducted experiments on rice-fish
farming in high, cold areas. Rice yields increased by 7.2-12.1%, and the survival
rate of fingerlings to harvest was 71.3-88.9%. The net value of the output
increased by CNY656-950/ha. Grass carp averaged 0.2 kg in weight; common
carp averaged 0.15 kg. Meanwhile, in Huanren County, Liaoning Province,
another rice-fish culture experiment stocked grass carp and common carp as major
species and tilapia as minor species in a 0.1-ha ricefield. They harvested 85.8 kg
of fish and rice yields increased by 7.3-8.4%.
8
RICE-FISH CULTURE IN CHINA
In 1985, Changchun City in Northeast China's Jilin Province raised common carp
fry during the summer in 4.3 ha of ricefields. They harvested 35000 fmgerlings
that measured 10-15 cm in length and weighed a total of 875.5 kg. The ricefields
yielded 279 kg of fish per hectare. The current situation (1986) of rice-fish
production in China is summarized in Table 2. There are almost 1 million ha of
rice-fish culture in China in 15 provinces and three municipalities (Beijing,
Shanghai, and Zhongging). In addition, experimental culture is being carried out
in the northern provinces of Jilin, Liaoning, and Heilongjiang and in the Xinjiang
Uygur Autonomous Region. Rice-fish culture is now practiced from southern
Guangdong and Guangxi at 22°N to Beijing at 40°N, and experimental activities
as far north as Heilongjiang Province (45°N).
The Development of Rice-fish Culture Techniques
Concept and Significance of Rice-Fish Farming
The new concept of "mutualism" in raising fish in ricefields is entirely different
from the traditional purpose and nature of rice-fish culture. The mutualism concept
is to improve rice production by letting herbivorous fish eliminate weeds that
compete with rice plants for sunshine, fertilizer, and space. At the same time, fish
in ricefields feed on weeds, plankton, and benthos, and form an optimum
ecological system that benefits both the fish and the rice. Traditionally, the idea
was simply to raise fish with rice as an additional source of food. Now the concept
includes the mutualism of both crops and has indeed become an effective way to
boost rice yields. There are two basic forms of rice-fish farming: (1) rotating rice
and fish, and (2) growing fish and rice together. Rice-fish rotation involves
growing rice one season and raising fish the next. This method has been
extensively adopted in winter ricefields, in fields that need to conserve water, and
in low-lying areas in Sichuan Province. The fish raised in these fields are mainly
adult or large fish.
The new concept of rice-fish farming combines the otherwise contradictory
principles of growing rice and farming fish. By making full use of the mutual
benefits of both rice and fish, the new concept provides a modern biological
technique to invigorate agriculture in China. The emphasis is on growing rice and
the role of the fish is to enhance the growth of the rice plants. But, the ultimate
goal is to increase the production of both rice and fish in rice-growing areas. There
are many advantages of growing fish with rice:
The fish increase rice yields by more than 10%;
A 0.07-ha ricefield can yield 300 fingerlings each measuring
10-16.5 cm. When table fish are reared, 150-450 kg/ha can be
harvested. In rice-fish rotation, more than 50 kg of fish can be
caught from 0.07 ha of surface water;
The fish feed on weeds and worms, and loosening up the soil. This
helps reduce labour requirements and is one of the outstanding
benefits of raising fish in ricefields;
REVIEW AND OUTLOOK
9
Table 2. The area (ha) of rice-fish culture in China (1981-1986).
Province or
Municipality
1981
1982
1983
1984
1985
1986
Beijing
—
—
1
21
7
7
Hebei
-
-
-
Shanghai
-
-
1
Jiangsu
-
-
26
Anhui
-
-
Zhejiang
-
Jiangxi
3333
15
15
100
23
83
23
3133
10886
14000
2666
10000
22666
34000
-
13353
17733
26486
18733
16666
18666
37800
52000
47000
19113
22353
28433
8766
6666
Fujian
-
-
14666
Henan
-
-
-
Hubei
1000
2333
3333
13333
28133
21653
20
Hunan
-
79666
112613
167100
188746
227000
Guangdong
-
4333
4000
5300
8120
13333
35333
31853
34546
45520
54200
1506
5700
Guangxi
20000
Shanxi
-
-
Sichuan
-
156666
192473
241393
282186
333333
Zhongging
-
-
54000
68666
78000
80000
Guizhou
94666
100666
106666
100000
66920
87333
Yunnan
-
-
8540
11560
10580
14000
564980
732467
854958
987500
Total
120980
397645
140
727
The fish (especially grass carp) conserve and enrich the fertility of
the water and soil and therefore stimulate the growth of rice plants
and increase grain yields;
The fish eliminate some insect and disease pests of rice, and in
addition eat mosquito larvae, which are pests to both animals and
people, and thus help to reduce the incidence of meningitis,
malaria, and filariasis.
10
RICE-FISH CULTURE IN CHINA
Rice-fish farming is closely integrated with freshwater fish farming in China,
especially in ponds, reservoirs, lakes, and family ponds. Freshwater aquaculture
requires increased quantities of fry. The demand for fry cannot be met by relying
on stock fish farms or by expanding stock fishponds.
The use of ricefields to grow fmgerlings has allowed the demand to be met. If the
area for rice-fish farming in China was expanded by 6.7 million ha, rice
production would increase by more than 2 million tonnes and 30-50 billion
fingerlings would be produced. This would also help increase the annual harvest
of freshwater fish.
Fish Species Stocked in Ricefields
In ancient times, the fish species stocked in ricefields were: common carp, crucian
carp, grass carp, silver carp and bighead carp. In the 1950s, the species used were:
black carp (Mylopharyngodon piceus), Chinese bream (Megalobrama
amblycephala), tilapia (Oreochromis mossambicus and O. niloticus), mud carp
(Cirrhina molitorella) in the south, loach (Misgurnus anguillicaudatus and
Xenocypris argentea) in Guangxi and Hunan, and snakehead (Ophiocephalus argus)
in Guangdong.
In the 1960s and 1970s, rainbow trout (Salmo gairdneri) were introduced in the
north, and catfish (Clarius leather) in the south. In the 1980s, the new species used
were: carp (Carassius auratus), aquatic crab (Eriocheir sinensis)\ shrimp
(Macrobrachium nipponensis), American snail, pearly clam, and field snail.
Increased Rice Yields After Fish Culture
There is considerable evidence that fish increase the yield of rice. Table 3
summarizes the information from a number of experiments throughout China. All
experiments show an increase in rice yield of 2-34% (average of 11.8%).
Chemical Insecticides Applied to Ricefields
There are over 50 pests and 10 diseases that attack rice. The major pests are:
yellow stemborer (Tryporyza incertulas and Chilo simplex), green rice leafhopper
(Nephatettix apicalis), rice plant skipper (Parana guttatus), and rice blast
(Piricularia oryzae), which is the most serious disease. Secondary pests and
diseases are: snout beetle (Echinocnemus squameus), rice leafroller
(Cnapholocrosis medinalis), yellow-legged lema (Lamaflavipes), locust (Oxya
chinensis), and brown spot (Cochliobolus miyabeanus).
In the early 1970s, chemical insecticides toxic to fish gained widespread use. Some
of these were 666, DDT, and limestone powder. Later, less toxic chemicals
(Roxin, Dipterex, Kitazine, and Fenitrothion) were produced. Methods of
application were improved to minimize damage to fish and to achieve the
maximum effect of the chemicals. For example, the water level in the ricefields
was increased before the chemicals were applied. Powdered chemicals were applied
REVIEW AND OUTLOOK
11
Table 3. Increase in rice production in rice-fish culture.
Experimental Unit
Increase
(%)
Year
Guiping, Guangxi
3.6-11
1957
Gaoxi, Lingling, Hunan Institute of Hydrobiology
4.8-13.4
1958
Hubei Agriculture Research Institute and Wuhan
Fisheries Research Institute
9315
9051
Guangxi Aquatic Products Experimental Station
8614.5
8697
Fujian Fisheries Research Institute Freshwater
Branch
4.6
1965
Southwestern Normal College and Qingshen
Hydroelectric Bureau, Sichuan Province
13.6
1976
15
1976
4.1-8
1976-1977
Shatou, Fanyu Counties, Guangdong
6-8
1978
Institute of Hydrobiology and Changsha
Agriculture Modernization Research Institute,
Academia Sinica
19.7
1979
Heyan, Taoyuan, Hunan
34
1981
Qing-guda Lake, Urumqi, Xinjiang
18
1984
Huanren County Broodstock Fish Farm, Liaoning
7.3-8.4
1984
Heilongjiang Academy of Agriculture Reclamation
Science, Heilongjiang
7.2-12.1
1984-1985
Zhulou, Yuanyang Counties, Hunan
Wenjia, Chendu, Sichuan
when the plants were covered in dew, and spray chemicals were applied when there
was no dew. In some areas, fish were driven to trenches or sumps before the
chemicals were applied. Insecticides were also applied in instalments or in patches.
Table 4 shows the current dosages of chemicals that are used.
Development of Rice-Fish Culture
Ricefields can be used as fish nurseries or to produce fish for food. In fingerling
production, either 450000-600000 eggs/ha or 300000 fry/ha of common carp are
stocked early in the season. By the summer, the fmgerlings are ready for harvest.
To nurture large-sized fingerlings, the stocking density should be
15 000-22 500/ha. If grass carp is the dominant species, 12000-15000 grass carp
should be stocked per hectare with 3 000-4 500 silver carp and bighead carp and
4500-6000 common carp and bream.
12
RICE-FISH CULTURE IN CHINA
Table 4. Dosages of chemicals applied in ricefields.
Common
(g/ha)
Chemicals
Dipterex
Maximum
(g/ha)
1500
2250
750
1500
Fenitrothion
1125
1500
Calcium methyl arsenate
3 000
3 750
Kitazine
1500
2250
750
1500
50
100
Chlordimeform
3 000
3 750
Jiangangmycin
2 250
—
Farmon condex
15000
18750
DDV
Methamidophos
Roxion
In Shanxi Province, rainbow trout was cultured in winter fallows by using slightly
running waters. Fish production was very high (30 t/ha). Rice-fish culture has
been practiced, not only in shallow-water ricefields, but also in deepwater rice
fields and in fields of wild rice (Zizania spp). In brackishwater along coastal
reclamation areas, a rotational system is used. One crop of rice is grown one year,
mullet (Mugil so-iuy) is cultured the next.
During the 1980s, several new developments occurred:
•
•
•
7
Ridge rice planting - ditch fish farming system. This system is
suitable for water-logged ricefields. The system involves a series of
ridges and ditch in the ricefield. The rice is grown on top of the
ridges and the fish in the ditch. The width of the ridge and the ditch
is 40 cm, the height of the ridge is 80 cm, and water depth is
50 cm.7
Rice-azolla-fish system. Rice is planted in the fields, azolla is
cultured on the surface of the water, fish are cultured in the water,
and squash or legumes are planted on the bunds. This is a multilevel
comprehensive system of resource use.
Running water system of trench fish farming. One or two broad
trenches (1-1.5 m in width and 60-90 cm in depth) are dug in a
ricefield. The trenches account for about 6% of the total area of the
ricefield, and fish are cultured in the water running through the
trenches.
The dimensions of the ridge-ditch system appear to vary considerably. The
ridge is often only 25 cm wide and 30 cm in height.
REVIEW AND OUTLOOK
13
Prospects for Rice-Fish Farming in China
China has 25 million ha of ricefields, and over 90% of this area is south of the
Huai He River Basin. Although the practice has achieved excellent results in terms
of scale and economic return, its potential to meet the needs of modern
development remains untapped. If 10% of the ricefields south of the Huai He
River were used (half for commercial fish and half for stocking fish), the
commercial fish yields could be 346000 tonnes (assuming 300 kg/ha) and the
number of full-size fingerlings would be 5 billion (assuming 4500/ha). The area
north of the Huai He River is not as suitable for rice-fish culture, but if 5% of the
rice fields become rice-fish systems, they would produce 8000 tonnes of
commercial fish and 243 million fingerlings. The total increase in rice output
would be one million tonnes annually on the basis of the 1981 output (if annual
increase is calculated at 10%) and commercial fish yields would reach
354000 tonnes and 5.7 billion fingerlings. The number of fingerlings raised in
ricefields would be sufficient to stock 0.75 million ha of water (e.g., ponds and
reservoirs). The achievement of these goals would have very large ecological and
economic benefits.
If fish farms were used to raise fry, ricefields were to be used to raise full-sized
species, and ponds, reservoirs, and lakes were used to raise adult fish, fish farming
would undergo considerable change. Fujian Province reported that, if ricefields are
used to rear fingerlings, 200 ha of stock fishponds would be freed for intensive
farming of commercial fish, and labour and feed, which would otherwise be used
for breeding fingerlings, could be used for commercial fish farming. Jiangsu
Province reported that, in 1986, Jianhu County used 4 700 ha of ricefields to raise
fish. Three major stock fish farms supplied enough fry to meet the need for
big-sized stock fish for 2000 ha of intensive fish farming in the county. This
indicates that the output of freshwater fish could be increased considerably.
Rice-fish farming has the potential to fully maximize the use of ricefields. Present
trends for popularizing the practice are encouraging, and the area used to grow rice
with fish is increasing yearly. In the past, the development of China's aquatic
products has been slow, quality has been poor, and supply was often short. There
have also been policy problems that remain unsolved. As the internal structures of
agriculture are adjusted, various localities are becoming aware that rice-fish
farming is an effective way to increase rice production and improve economic,
social, and ecological conditions.
Since the national conference on rice-fish farming in 1983, various provinces,
autonomous regions, and municipalities have undertaken measures to popularize
the practice in line with local conditions. The Science Commission and Aquatic
Products Department of Fujian Province organized several research projects. They
achieved success by strengthening their leadership and by coordinating technical
forces. East China's coordinating group met once a year to summarize work
experiences and coordinate actions. Representatives from various provinces visited
advanced units to draw on their experiences and to increase the awareness of
leaders from different areas about the significance of rice-fish farming. They held
14
RICE-FISH CULTURE IN CHINA
meetings to discuss the practice and conducted training courses to expand the area
of ricefields for fish farming.
Rice-fish farming should be combined with intensive fish farming in ponds,
reservoirs, lakes, and cages to ensure that more fingerlings can be raised in
ricefields. Recently, a national symposium called for the rapid development of
ecological agriculture to improve productivity. Ecological agriculture has received
increased attention in recent years, and the structure for agricultural production has
been improved significantly. Undue emphasis used to be placed on plant culture;
however, attention has now shifted to the comprehensive development of farming,
forestry, animal husbandry, and fisheries. Instead of focusing only on economic
results, both economic and ecological benefits are now considered. In the past,
single items of technology were emphasized. Today, due attention is given to the
comprehensive application of technical packages.
Rice-fish mutualism offers a model of ecological agriculture. However, fish
farming has not yet been closely integrated with crop cultivation and the division
of labour has not been clear; therefore, development and popularization have been
slow. The production of both rice and fish can be maximized if agricultural
researchers pay more attention to rice-fish farming and help hasten its
development. It is imperative to integrate fish farming with crop cultivation. If the
area for rice-fish farming was increased to 6.7 million ha as the area devoted to
rice is increased, the supply of freshwater fish could be quadrupled.
Rice-fish farming can play an increasingly important role in freshwater fish
farming if the nation's leaders give it due attention, if the technology is sound, and
if the practice is carefully adapted to local conditions.
Rice-Fish Culture in China: Present and Future
Chen Defu and Shut Maoxing8
In China, fish are raised in ricefields in the southeast and southwest mountainous
areas where there are few bodies of water for growing fish and fishing regions and
towns are far away. Rice-fish culture is a traditional and popular way for the
people to grow their own supply of fresh fish in the mountainous areas of: Qingtian
and Yongjia in Zhejiang Province; Jiening, Taining, Saxian, and Yongan Shaowu
in Fujian Province; Yulin, Guilin, and Jinzhou in Guangxi Province; the southern
part of Guizhou Province; and Pingxian, Jian, and Yichun in Jiangxi Province.
In these areas, the farmers practice rice-fish culture to raise fish for their own
consumption, although it requires extensive management and fish harvests are
poor. Before 1949, there was no organized extension of the technology; therefore,
rice-fish culture did not improve.
Present Situation
Extension of Rice-Fish Culture
Since the founding of the People's Republic of China in 1949, the government has
paid more attention to rice-fish culture. In 1954, the First National Conference on
Aquatic Products formally called for the promotion of rice-fish culture. The area
devoted to rice-fish culture increased rapidly and reached over 670 000 ha by the
end of the 1950s. During the mid!950s to the early 1960s, rice-fish culture
developed rapidly in the mountainous areas of south and north Zhejiang and in the
plains and hilly areas of Shaoxin, Jin Hua, and Hangzhou. However, this
development suffered a major setback during the 1960s to the mid 1970s when
planting systems were reformed and highly toxic pesticides were used. The area
devoted to rice-fish culture decreased drastically, but began to increase slowly by
the end of the 1970s as improved breeds of rice and less toxic, but effective,
pesticides were introduced. In the 1980s, more farmers became interested in
rice-fish culture as the government encouraged its adoption and introduced a
family contract system in rural areas.
In 1983, the office of the Central Committee of Patriotic Hygiene in Xinxiang
City, Henan Province, held a meeting about controlling mosquitoes in ricefields.
They decided to promote and disseminate information about rice-fish culture and
to advance its development.
8
Soil and Fertilizer Institute, Zhejiang Academy of Agricultural Sciences,
Hangzhou, Zhejiang Province.
16
RICE-FISH CULTURE IN CHINA
The first national meeting on rice-fish culture was held by the Ministry of
Agriculture, Husbandry and Fishery in Wenjiang County, Sichuan Province, in
August 1983. Similar meetings followed in provinces, cities, and autonomous
regions. Rice-fish culture in China began a new period of rapid development. The
total area of rice-fish culture increased 65% between 1983 and 1984. In Zhejiang
Province, the total area9 was 18127 ha in 1984, a 36% increase from the 12 353 ha
in 1983.
In 1984, the Bureau of Aquatic Products of the Ministry of Agriculture, Husbandry
and Fishery organized and launched a project "Extending the Techniques for
Fish-Raising in Ricefields" in 17 provinces, cities, and autonomous regions The
total area for rice-fish culture in the country increased to 846 700 ha in 1985 and
to 985 300 ha in 1986 and had a positive effects on the economy, society, and
ecology. The project received the first grade award for advanced scientific
technology from the Ministry of Agriculture, Husbandry and Fishery in 1986.
Rice-fish culture has now developed and been adopted in the southeast and
southwest mountainous areas and the plains, and the northeast and northwest
regions. It is practiced in the ricefields of Sichuan, Hunan, Guizhou, Chongqing,
Guangxi, Jiangxi, Anhui, Fujian, Zhejiang, Jiangsu, Yunnan, Guangdong,
Henang, Shaanxi, Hebei, Xingjiang, Liaoning, Helongjiang, Beijing, and
Shanghai.
Research on Rice-Fish Culture
Since 1949, the main research areas in rice-fish culture have been:
•
•
•
•
•
9
The relationship between rice and fish and ways to increase rice
production using rice-fish culture;
The different forms of the ricefield that can be used for rice-fish
culture (plain, ditches, pits, wide ditches, and ridges);
Suitable breeds of fish (i.e., grass carp, common carp, crucian
carp, murrel, and mud loach). A few silver carp and bighead carp
can be raised together with these fishes in ricefields with wide
ditches. The raising of grass carp is the most effective way to clear
up weeds and pests. Adult grass carp grow quickly in ricefields;
therefore, fish yields and economic returns are increased.
Techniques to prevent grass carps from injuring the rice plants must
be used;
Comprehensive techniques to improve harvests from riceazolla-fish systems;
Economic evaluations;
In some cases the areas differ from the summaries presented in Tables 1
and 2 of the previous paper by Cai et al. The editors have retained the figures
presented by the individual authors.
REVIEW AND OUTLOOK
•
•
•
•
•
17
Suitable pesticides, their safe dosage, and methods of use, and the
residual effects of methamidophos, carbofuran, and insect-paste in
the rice-azolla-fish system;
The control of mosquitoes in ricefields using fish-raising, and the
development of the rural economy;
Comprehensive techniques to efficiently manage agriculture, animal
husbandry, and fisheries;
The rates of absorption, transfer, and application of N and P, and
the use of azolla by fish; and
Feasibility studies.
Types of Rice-Fish Culture
There are two ways to combine rice and fish:
•
•
Rice and fish together. Planting rice while raising fish is the main
method used. The method makes full use of time, space, energy,
and resources of the ricefield and provides economic benefits. Its
shortcoming is the rather high requirement for labour and
management.
Rice and fish in rotation. Planting rice and raising fish are carried
on alternately; therefore, the contradictions between growing rice
and raising fish are avoided. After the rice is harvested, fish are
raised in deepwater fields, which can improve fish yields. The
disadvantages are that the growing period for the fish is shortened,
and that the mutually beneficial and efficient relationship of
rice-fish culture is lost. In regions with two rice harvests, the
rotation of rice and fish will reduce rice yields.
The main methods of the rice and fish rotation are:
•
early rice - late fish;
•
earlyfish- late rice;
•
after the harvest of one rice crop, fish are raised in deep water;
• fish are raised in clean summer fields for 1.5-2 months after the
harvest of early rice and before the late rice is transplanted;
•
fish are raised for 120-130 days in clean winter deepwater fields
after the annual harvest of late rice (the fish are caught the
following year before the early rice is transplanted); and
•
in the same ricefield, two harvests of fish are raised and two crops
of rice are planted during the same year (i.e., early rice - raising
fish in summer, and late rice - raising fish in winter). In
Guangdong Province, summer fish are raised for 40-50 days,
winter fish for 80-100 days.
18
RICE-FISH CULTURE IN CHINA
Yields and Techniques
Fish yields in ricefields have been low. The average yield of fish per hectare from
1982 to 1987 was 70.5, 82.5, 100.5, 126, 141, and 133.5 kg, respectively. New
techniques and high-yield demonstration plots all over the country have led to
increased fish yields. However, average yields in large areas of the country are still
low. Traditional techniques of rice-fish culture are still used in most parts of
China.
The reasons for low yields of fish from ricefields are:
•
•
•
•
•
•
•
Low water volume and little shelter. Traditionally, ricefields used
to raise fish do not have ditches or pits. The low volume of water
in these ricefields results in insufficient dissolved oxygen and few
plankton, high water temperature in summer, and few places for the
fish to hide from predators. The density of the fish, the rate of
catching, and yields are limited.
Inbreeding of fish and genetic degeneration. Carp are raised in most
ricefields in China. For example, Tian carp are popular in south
Zhejiang, West Hunan, and Sichuan, Gao Bei carp and Jin carp are
popular in the mountainous area of Guizhou, "Hehua" carp are
popular in northern Guangxi. These breeds of carp have mild
characteristics and do not jump well; therefore, they cannot escape
easily. They are suitable for raising in ricefields. However, because
of prolonged inbreeding, the breed characters have degenerated and
the fish grow slowly.
Small fish breeds. The old regions of rice-fish culture use the
traditional method in which small fish are raised and, in some
regions, fingerlings are stocked directly into the field. This has led
to slow growth of fish and low survival rates.
Insufficient feed. Artificial feed is not used in the traditional
method. However, there is insufficient natural feed in ricefields,
especially in mountainous areas. The weeds decrease as the fish
grow; therefore, the fish do not get a sufficient supply of weeds
during the middle and late growing stages of the rice.
Low density of fish. For breeding, 10500-22500 summer
fingerlings are raised per hectare. For food, 1500-7500 summer
fingerlings and 750-1200 spring fingerlings are raised per hectare.
Late stocking, early harvest, and short growing periods. Fingerlings
are usually stocked a week after the rice seedlings are transplanted
and the fish are caught during the rice harvest. The period for the
rice and fish to grow together is short — about 90 days in regions
with one rice crop and 160-180 days in regions with two rice crops.
In southern China, 240 days (Jiangsu) and 330 days (Guadong) are
considered suitable.
Once raising and once catching. The fish carrying capacity in
ricefields changes during the growing period. Early in the season,
the field has many weeds and the fish are small; therefore, the
REVIEW AND OUTLOOK
•
19
natural feed is sufficient. Later, when the fish are larger, there are
fewer weeds. The resources in the field no longer match the density
of the fish.
Small-scale production. The farmers consider the fish a by-product;
therefore, the area used to raise fish in ricefields is small and
scattered.
The Rise of Modern Rice-Fish Culture
Traditional rice-fish culture is no longer suited to the country's social
development, and it hampers the extension of modem methods of rice-fish culture.
In the 1980s, several reforms were made:
•
•
•
•
•
•
•
The layout of the ricefields used to raise fish was improved. The
traditional plan was changed to include ditches, wide ditches, pits,
and ridges. The volume of water was increased to improve the
environment for the fish.
Several breeds of fish are now used instead of a single breed. Fish
(e.g., grass carp, common carp, nile tilapia, silver carp, variegated
carp, and crucian carp) were selected to suit local conditions.
Fish size was increased. Fingerlings 10-cm or larger are now used
instead of fingerlings 6-8 cm in length.
Stocking density of the fish was increased. Depending on the
fertility of the soil and feed supply, 4 500-6 000 adult fish from the
previous year and 3 000-4 000 summer fingerlings are raised per
hectare. The numbers can be increased if conditions are improved.
Shifting from late stocking - early harvest to early stocking - late
harvest. Because the ditch, pit (pool), and ridge systems have
permanent fish pits, fish-raising can begin in the winter. Fish are
now raised continuously after the harvest of late rice in deep-water
ricefields. If crops are planted in winter for spring harvest, fish are
caught 2 weeks before wheat or rapeseed are planted.
Feed or the rice-azolla-fish method are used instead of not feeding
the fish.
One-time raising and one-time catching were changed to alternative
catching and raising.
The new techniques have improved average yields to 750-3 000 kg of fish per
hectare while increasing rice production. The highest fish yield reached 5 500 kg/ha
in two-crop ricefields in Zhejiang. These new approaches have helped to modernize
the traditional methods of rice-fish culture in China.
Prospects for Rice-Fish Culture
Potential
Because of the country's large population and limited agricultural land, agriculture
in China is moving toward intensification. Rice-fish culture is part of this
20
RICE-FISH CULTURE IN CHINA
intensification. It is an effective way to increase the productivity of ricefields by
harvesting both rice and fish. It is the quickest method to increase the economic
efficiency of the ricefield and to help farmers increase their income.
There are about 25 million ha of ricefields in China. If 30 %10 were to be used to
raise fish, about 7.5 million ha would be available for rice-fish culture. If 600 kg
of rice and 375 kg of fish were harvested per hectare, this would increase the
country's production to 45 billion kg of rice and 28 billion kg of fish. Less than 1
million ha of land, or 3.9% of the total area of ricefields, are now devoted to
rice-fish culture. Therefore, there is great potential to develop rice-fish culture.
The rapid development of township industries has improved the skills of farmers.
The development of family farms has prepared favourable conditions for the
large-scale management of rice-fish culture using advanced scientific techniques.
A modern and effective rice-fish industry will alter traditional concepts about
rice-fish culture and encourage more farmers to raise rice and fish together.
Factors Limiting Development
•
•
•
•
•
10
Fish can only be raised in ricefields with sufficient water resources
and good irrigation and drainage. Poor water resources, drought,
serious leakage, and poor water-holding capacity of the soil make
rice-fish culture difficult in north China; whereas, south China is
rainy and flood-prone.
Higher economic efficiency can be achieved in township industries
and trade businesses than in areas that practice traditional methods
of rice-fish culture.
The family-contracted fields are scattered and on a small-scale.
Advanced and scientific methods of rice-fish culture are difficult
for farmers to adopt without further land consolidation.
Support systems for rice-fish culture are inadequate. It is very
difficult for farmers to obtain loans, new and improved fish breeds,
feed, fertilizer, and pesticides. There are also few technicians
available to instruct farmers. Therefore, the breed characters of
some carps that are popular with farmers degenerate and as a result
the fish grow slowly.
For a long time, traditional techniques have hindered the
development of rice-fish culture because they prevent farmers from
accepting and grasping modern techniques. Farmers worry that fish
pits and ditches will affect grain yield. These ideas hamper the
extension of rice-fish culture.
Different authors suggest various levels for potential expansion of
rice-fish culture in China. The estimates in this paper are probably overly
optimistic because only about 25% of the rice area is suitable for rice-fish culture.
REVIEW AND OUTLOOK
21
Strategies for the Development of Rice-Fish Culture
Rice-fish culture must be given as much attention as the production of food grains,
and should be seen as a way to develop grain production and to improve the
economic conditions of farmers. Several tactics can be used to improve rice-fish
culture:
•
•
•
•
The efficiency of rice-fish culture, and the area devoted to rice-fish
culture in traditional regions, should be increased through technical
training and increased funding.
Testing sites should be established in plain areas and modern
techniques should be extended to farmers to increase yields of rice
and fish, and to spark interest in rice-fish culture in these highproduction rice areas.
Rice-fish culture should be extended to large farm families who
mainly grow rice. The technology could help improve their
livelihood and become pioneers in the large-scale development and
efficient management of rice-fish culture in the country.
Agricultural and aquatic products units should be merged to
coordinate research and improve extension of practical techniques
for rice-fish culture. The basic theories of rice-fish culture and
techniques for good harvests of both rice and fish must be studied.
This page intentionally left blank
Scientific and Technological Development of Rice-Fish
Culture in China
Zhang Rongquan11
Rice-fish culture is an organic method that integrates
aquaculture. It enhances the growth of both rice and fish,
field and water resources, and effectively increases harvests.
technological developments have been made to rice-fish
China.
rice production and
maximizes the use of
Several scientific and
culture techniques in
Development of Rice-Fish Culture Techniques
Traditional Aquaculture Techniques in Ricefields
Historical records show that Chinese farmers started raising fish in ricefields more
than 1700 years ago. But despite its long history, rice-fish culture did not progress
for many years and its development was hindered by feudal relationships. Farmers
raised fish in ricefields as a sideline, usually only to augment their own meals.
Rice-fish culture is described in the Tang Dynasty treatise (about 889-904 AD)
Wonders in Southern China by Liu Xun:
... after the spring rains, water collects in the fields lots around the houses.
Grass carp fingerlings are then released into the flooded fields. One or two
years later, when the fish are grown, the grass roots in the plots are all
eaten up. This method not only fertilizes the fields, but produces fish as
well. Then, rice can be planted without weeds.
During the Ming and Qing Dynasties, rice-fish culture gradually developed into
an important sideline in the countryside. But, because of various restrictions, it did
not grow into an organized technique. Operations were often scattered and little
information was available; therefore, methods and yields varied considerably in
different areas. Yields were low and the scale of production and the techniques did
not progress.
Before the founding of the People's Republic of China, the Ministry of Agriculture
and Forestry of the Kuoming-Dang Government promoted the development of
rice-fish culture by stocking fingerlings in ricefields of Sichuan. They also
published and distributed a brochure entitled An Elementary Introduction to
Rice-Fish Culture. In Shong Jiang District, the Jiangsu Province Rice Experiment
Station conducted experiments on rice-fish culture and provided technical guidance
11
Chinese Academy of Fisheries Science, Wuxi, Jiangsu Province.
24
RICE-FISH CULTURE IN CHINA
to local farmers. These efforts promoted rice-fish culture locally, but restrictions
limited its impact on the rest of the country.
During the early period of the People's Republic of China, rice-fish culture
flourished as agricultural production was restored. Experiences in rice-fish culture
were exchanged quickly and more districts began to adopt the technique. By 1959,
the total area devoted to rice-fish culture had increased to about 670 000 ha. At this
stage, fish were raised on a small-scale with traditional tall rice varieties grown
without pesticides on level land. A few farmers dug fish ditches, which took up
only 1 % of the field area. The species raised were restricted to grass carp and
common carp. Usually, the fish were not fed and only weeds were available.
Production, efficiency, and benefits were low. Although there were new
developments, rice-fish culture remained very traditional.
In later years, the system of rice cultivation was reformed and large quantities of
fertilizer and toxic pesticides were used. Rice-fish culture decreased. Since 1978
new techniques have been developed.
New Techniques
China is very large and the natural conditions vary substantially between different
regions. Since the 1970s, the coexistence of rice and fish had been established
based on the traditional system of rice-fish culture. However, reforms in the ricegrowing system and progress in rice-fish culture techniques have intensified the
conflicts between rice and fish culture. The traditional techniques did not suit the
new situation and this hindered the development of rice-fish culture.
In 1972, Ni Dashu of the Institute of Hydrobiology, Academia Sinica, put forth the
theory of feeding fish for rice culture. Later Ni Dashu and Wang Jianguo
developed a theory of mutualism that stated that rice and fish could coexist. They
conducted experiments on rice-fish culture. Ni Dashu studied the rational use of
ricefield resources and deemed that although there were differences in growth and
development of rice and fish, they shared common characteristics in terms of their
need for water, light, and fertilizer.
Fish were fed in ricefields, and fish-raising was integrated with rice culture. Rice
was regarded as the main product, and the biological productivity of ricefields was
upgraded. Ricefields were used, not only to raise a single crop, but to grow several
crops. Rice and fish could coexist in the same field. Bumper harvests of both rice
and fish provided more protein, improved efficiency, and increased economic
benefits.
In the 1980s, rice-fish culture made progress. Guided by the mutualism theory of
rice and fish, scientific and technological workers developed many new techniques
for shallow irrigation fields and adjusted the use of pesticides and fertilizer
according to the new production structure and to changes in techniques of rice
culture. Many new species of fish were used: grass carp, common carp, crucian
carp, Beijing bream, silver carp, bighead carp, and tilapia. New techniques were
REVIEW AND OUTLOOK
25
developed that could produce yields of over 7500 kg of rice and 750 kg of fish per
hectare.
Rice-fish culture techniques can be divided into three categories: growing rice and
raising fish together in the same field, rotating rice and fish, and continuing fish
culture in the ricefield after the rice is harvested. In some areas, all three forms are
combined. According to engineering facilities, rice-fish culture can be further
divided into: feeding fish in furrows and growing rice on ricefield ridges, using
ditches, pits, or ditches with flowing water, and additional techniques, such as
raising fish and azolla together in the ricefield and raising fish and ducks at the
same time in the ricefield.
Rice-fish culture, rotation of rice and fish, and continuous rice-fish
culture. In rice-fish culture, rice and fish live together in the same field. This
technique can be used with early rice, midseason rice, and late rice. Some
contradictions between growing rice and raising fish are unavoidable. Therefore,
fertilizer and pesticides that can harm the fish are avoided. Generally, excessive
engineering facilities are not necessary. Fish feed is not needed because the fish
live on natural food in the ricefield. This is extensive culture. Average production
is about 150 kg/ha and well-managed fields can produce over 750 kg/ha. The
disadvantage of this technique is that the growth period of the fish is comparatively
short and the harvested fish are small. Therefore, large fingerlings are usually
used. The technique is occasionally used to stock adult fish for 1 year.
In a rotation of rice and fish, the fallow field left after the rice is harvested is used
to raise fish. Generally, fish fry or fingerlings are stocked. After the rice harvest,
the straw is left in the field. When the land is irrigated, the straw decays, which
makes the water suitable for feeding adult fish. In this form of rice-fish culture,
fish have more space to move about and it is convenient to spread feed, but the
growth period is relatively long. Compared with raising rice with fish, production
of fish is higher. Generally, fish yields are 300-450 kg/ha with maximum yields
of over 1500 kg/ha. Because it provides remarkable economic benefits, rotation
of rice and fish is widely used in fallow winter fields, during the summer with
green manure crops, for stocking fingerlings to produce table fish, and in seedling
beds to stock fish fry for fingerling culture.
In continuous rice-fish culture, rice and fish are raised together. Because the fish
are raised after the ricefield is fallow, their growth period may be over 1 year,
which produces better results. Generally, production reaches over 750 kg/ha. This
form of culture is widely used in hilly and mountainous regions.
In practice, a combination of these techniques adapted to suit local conditions
achieves the best results.
Other techniques. Fish can be raised quite successfully in furrows in
ricefields. This method is based on a half-dry cultivation method developed by Hou
Guang-jiong. It effectively transforms uncultivated ricefields and can increase rice
production in low-yielding fields (e.g., fields in the foothills, cold fields, and
26
RICE-FISH CULTURE IN CHINA
water-logged fields). The ridges in the field can be thickened with layers of soil,
and the water in the field can be made deeper. This raises the temperature of the
soil, improves soil structure, promotes seedling growth, and improves water
management. The fish help reduce diseases, pests, and wild grass and as a result,
rice production is increased by 10-20%.
Fish can also be raised in ditches that contain water that is deeper than in the
surrounding fields. Fish screens and ditches and pits in the centre of the field help
improve the environment for the fish. Fish production in ditches is generally two
to three times higher than in level fields.
In integrated fish culture in ditches and pits, pits are dug in the ricefields or along
the side of the field and are connected with ditches. Fish are raised in the pits and
ditches. This technique was developed after the contract-responsibility system was
implemented for family operated rice-fish farms. The method offers several
advantages. It improves water management, assures a good harvest, maximizes the
use of pits in the field, and helps resolve conflicts between rice and fish caused by
operations such as shallow irrigation, drainage of fields, and the use of chemical
fertilizers and pesticides. The water in the pits helps the rice resist drought and
provides a guarantee of steady rice production. The pits also provide more space
for the fish, which enhances fish growth and improves yields.
If the pits are used as nursery ponds, the fry develop into fingerlings earlier, which
reduces transportation costs for fingerlings. The pits also provide a capture area
during harvest. Production is increased and farmers save work and time.
The technique of raising fish in ditches with flowing water is based on flowingwater aquaculture. It is a semi-intensive rice-fish culture technique that is used
mainly in ricefields with good irrigation and sufficient water resources. Wide
ditches are dug and a small flow of water is led into the ricefield. Because intensive
aquaculture techniques and principles have been adopted, production is
comparatively high. Farmers are adopting this technique rapidly in areas with the
required water resources.
Rice-azolla-fish cultivation involves growing rice, fish, and azolla at the same
time in the same field. This cultivation technique makes full use of space and
water. The ricefield provides a good environment and rich food for the fish.
Azolla, which grows on the water surface, provides feed for the fish and manure
for the field. The fish eat pests and weeds and their excretions fertilize the field to
improve the growth of rice.
Several other farming methods have also been developed to maximize the use of
ricefield resources and involve rice-fish culture (e.g., growing various beans on
the ridges of the field and herding ducks in the ricefield).
REVIEW AND OUTLOOK
27
Comparison of New and Traditional Techniques
Many developments have been made in the new technique for rice-fish culture.
The traditional techniques are integrated into the rice-growing systems found
throughout China. This ensures that rice-fish culture is practiced across China.
However, the traditional technique does not suit all rice-growing systems. Because
there is only one model, it is difficult to extend and develop this model of rice-fish
culture throughout all regions of China.
The new techniques include advanced culture and engineering features adaptable
to local conditions. Effective engineering facilities help avoid conflicts between
rice and fish and improve the ability of the ricefield to resist drought and flood.
Rice production is therefore guaranteed along with substantial increases in both rice
and fish harvests. The traditional technique cannot resolve or avoid conflicts
between rice and fish. Sometimes fish must be sacrificed to guarantee rice
production. This reduces income and discourages initiatives in rice-fish culture.
The new techniques apply lessons learned from alternative aquaculture techniques
and new developments with respect to stocking size, variety, management,
multispecies culture, feeding, and maintenance of water quality using fertilizers.
These developments, together with a certain degree of intensification, play a
positive role in improving fish production. The traditional technique does not
involve these new aquaculture techniques and harvests of both rice and fish are not
as good.
The new techniques fully apply the principles of rice-fish mutualism and soil
thermodynamics. Different disciplines and the technical systems of farming and
aquaculture are organically integrated. The effects and benefits of economics,
sociology, and ecology are unified to promote the development of the rice-fish
culture system. The traditional technique does not organically combine agriculture
with aquaculture. Because the technical system for rice-fish culture is not perfected
steady development of rice-fish culture cannot be assured. Moreover, because the
new technique has led to increased harvests of adult fish, it has established the
technical foundation for rice-fish culture to move from a self-sufficient economy
to a commodity economy.
In 1983, the area for rice-fish culture in China was 441000 ha. In 1987, it
increased to 796667 ha with 106000 tonnes of fish production.12 At present, the
area for rearing adult fish (excluding fingerling rearing) in ricefields is 708 027 ha
with a total production of 124900 tonnes and an average production of 180 kg/ha.
This rapid rate of development is directly related to technical advances in rice-fish
culture.
12
etal.
These figures differ from those presented in Table 2 of the paper by Cai
28
RICE-FISH CULTURE IN CHINA
Constraints to Rice-Fish Culture
Despite great advances, several technical and production constraints must be
resolved:
•
•
•
•
•
The new technique has not been properly extended to farmers and
there is a considerable yield gap between experimental models and
the yields achieved by farmers. Some models yield over
3 750 kg/ha, but farmers obtain yields of 150-300 kg/ha.
Fry andfingerlingsupply is insufficient.
The composition of the species for stocking and stocking density
must be more fully studied.
Feed management must be improved to raise unit yields.
Weaknesses in fisheries management discourage initiatives taken by
farmers in rice-fish culture.
Development of Rice-Fish Culture Techniques
Experience has proven that rice-fish culture is beneficial. Large amounts of fresh
fish can be harvested, while the production of rice increases. In some cases, the
production value of fish exceeds that of rice. Rice-fish culture therefore offers
potential for China, a country with limited land and a large, growing population.
The country must develop this potential for food production, while increasing the
income of farmers. China's demand for grain and fish products will likely continue
to increase.
There are no marketing problems for the products of rice-fish culture, and income
is higher than from growing rice alone. Therefore, farmers are eager to develop
rice-fish culture because of the demand for food and the increased economic
benefits that can be realized.
Rice-fish culture in China combines the principles of water conservation, soil
improvement, and biological control into an integrated technique for rice-fish
production. The new technique will play a important role in land management and
environmental protection. Rice-fish culture techniques are expected to develop
rapidly in several areas.
Basic Techniques of Rice-Fish Culture
The rice-fish mutualism theory advanced the development of rice-fish culture.
When other disciplines were integrated into rice-fish culture, the theory was
further developed and improved. It is important to study the mechanisms of
rice-fish culture, the natural laws governing aquaculture and agriculture, and the
interrelationships among rice and fish, and other factors such as soil, water, and
fertilization in the ricefield.
REVIEW AND OUTLOOK
29
Rice Growing and Aquaculture
The study of the interrelationships between rice and fish will help understand the
contradictions between the two production systems and find ways to enhance the
harmony between agriculture and aquaculture and to improve yields for both rice
and fish.
Integrated Rice-Fish Culture Techniques
Rice-fish culture techniques must be integrated with alternative aquaculture (e.g.,
intensive pond aquaculture, lakes and reservoirs aquaculture, cage aquaculture, and
other supporting techniques). This will help increase production per unit area and
maximize the widespread practice of rearing fingerlings in ricefields.
Engineering for Rice-Fish Culture
To strengthen the capacity of rice-fish production systems to withstand natural
disasters, rice-fish engineering facilities should be integrated with techniques of
water conservation. Engineering facilities should also be flexible and adaptable to
local conditions.
Management Model for Rice-Fish Culture Techniques
The economic benefits of the different rice-fish culture techniques that are
practiced in different areas should be analyzed. Management methods for rice-fish
culture must be studied to establish an economic model of rice-fish culture that is
adaptable to local conditions, requires less input, but yields increased output.
There are 25 million ha of ricefields in China. Of these, about 10 million ha are
suitable for rice-fish culture. If integrated rice-fish farming was further advanced
by effective extension work, the area for rice-fish culture in China could be
increased by several million hectares within this century. It would then be possible
to produce the substantial quantities of fingerlings and adult fish needed to supply
further development of freshwater aquaculture in ponds, lakes, and reservoirs.
Rice-fish culture will play a vital role in freshwater aquaculture, in the commercial
economy, and in agriculture. It will produce food for China and the world.
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Development of Rice-Fish Farming in Guizhou Province
Shi Songfa13
Rice-fish farming has been practiced for over 1000 years in Guizhou. It is most
popular in eastern Guizhou (bordering the provinces of Hunan and Guangxi) in
areas where communities of national minorities live. The most commonly
cultivated species are "Gaopo" common carp and "river" common carp. Farmers
gather fish eggs from ponds, ricefields, and rivers and hatch them to get fry.
Because of climatic conditions, most areas have only two crops a year with a single
crop of rice. Fish are cultivated at the same time as rice. Flat fields and extensive
cultivation are the norm. Normally, fields are not drained and the farmers in
southeast Guizhou even cultivate fish in the winter water fields.14
In 1984, the Departments of Aquatic Products, Soil and Fertilizer, and Agricultural
Extension were organized to promote high-yielding techniques for rice-fish
farming. A number of technical guidelines, such as the Technical Rules for
Rice-Fish Farming and Technical Standards for Cultivating Fish in Ridge BoxDitch Ricefields were published. Many demonstration plots were developed.
By 1987, there were over 3000 ha of high-yield demonstration plots (a 13-fold
increase from 1984). The average yield was almost 400 kg/ha (40% more than in
1984). With these encouraging results, rice-fish farming developed rapidly. In
1980, 42700 ha of ricefields yielded 3348 tonnes of fish, by 1983, this had
increased to 60000 ha and 4611 tonnes offish. In 1987, there was a 75% increase
in area and a 210% increase in yield (74 700 ha and 10400 tonnes of fish). This
amounted to 57% of the total fish production of Guizhou in 1987. The unit yield
also increased 78% from 1980 to 1987 and reached 139 kg/ha.
Development Trends
With popularization and technical extension, rice-fish farming has improved the
ecological environment of the ricefield and is making better use of the carrying
capacity of the field and achieving additional benefits from low-level inputs.
13
Aquatic Products Division, Guizhou Aquaculture Bureau, Guiyang,
Guizhou Province.
14
Winter water fields are ricefields that are left fallow and collect water
during the winter. Rice is transplanted to these fields in the spring. This practice
is prevalent in the cooler, mountainous areas of western China, particularly in the
provinces of Sichuan and Guizhou.
32
RICE-FISH CULTURE IN CHINA
New Rice-Fish Farming Techniques
Flat-field techniques of rice-fish farming have been replaced by ridge-ditch
ricefields (in which the fish are grown in the ditches and the rice is grown on the
ridges), box-ditch fish raising, and manure-pit fish raising in flat fields. Instead of
farming fish only with rice, farmers now also grow wild rice or lotus.
Fish farming in the ridge-ditch fields does not require inundated irrigation,
therefore, the conditions of water, fertilizer, oxygenation, and heat are improved
in the soil. This has considerable impact on the rice. It stimulates the early growth
of seedlings and early emergence of tillers. The grains of rice increase in number
and size, which produces higher yields. This practice also increases field-water
storage, improves drought-resistance capability, and provides sufficient deep water
for fish. These factors all improve fish growth and lead to higher yields.
The Scientific Association of Southeast Guizhou Prefecture, the Information
Institute of Scientific Committee, and the Prefecture Agricultural Institute
conducted experiments in 1986 to observe the differences between ridge-field rice
and flat-field rice. They found that there were considerable changes to the soil
environment that affected the growth of the rice plants. Soil temperature in ridge
fields was normally 0.2-0.4°C higher than in the flat fields. Results were
particularly obvious in cold, muddy fields that had low soil temperatures. Growth
was faster in ridge-rice cultivation. Seedlings recovered quickly after transplanting
and tillers emerged 9 days earlier than in flat fields. The activity of soil
microorganisms was also enhanced, which improves the breakdown of soil
nutrients and helps provide adequate nutrition for root growth. With improved
vitality, rice roots grew deep into the soil and the roots were stronger. During the
tilling period, rice roots in the ridge fields were 8 cm longer than that in flat fields,
and on average there were 20 more roots. During the full-ear period, the roots of
plants on the ridges were 13 cm longer and there were 199 more roots. Ridge-rice
cultivation can also enhance the resistance of the rice plant to drought and lodging.
When fish and rice were grown together, topsoil fertility in ridge fields was
significantly higher. There were increases of 0.55% in organic matter, 0.022% in
whole nitrogen, 1.2 mg/100 gt in hydrolytic nitrogen, and 27.7 ppm in effective
phosphorus.
Experiments carried out in 1986 by the Aquatic Products Station of Chishui County
revealed that ridge-rice cultivation could improve rice tillering and increase average
grain weight. In these experiments, the average number of grains per ear in the
ridge fields was 140-155 compared with only 105-110 in flat fields. The average
weight of 1000 grains in the ridge fields was 27.5-28.4 g, compared with
26.5-27.0 g for flat fields. The empty grain rate was 26.5-28% in the ridge fields
and 39-41 % in the flat fields.
Additional evidence of the benefits come from farmer experiments. A farmer,
Jiang Chengxu in Suiyang County, conducted a comparison trial in an area of
0.05 ha (0.025 ha for each of the two methods). In each area, he stocked 200 7-cm
fmgerlings. The flat field yielded 170 kg rice and 12.6 kg fish. The ridge field
REVIEW AND OUTLOOK
33
yielded 200 kg rice and 34 kg fish, or an increase of 18% for rice and 172% for
fish. In the Southeast Guizhou Prefecture, ridge-field cultivation required 6-8 more
farmer-days of labour, but the value of production increased by 50%.
Raising of fish in box ditches and manure pits in flat fields can also create a good
ecological environment for fish because pesticides are not applied and exposure to
sun and drought is reduced. This system increases the potential of the ricefield and
produces higher fish and rice yields. Manure pits normally only occupy 10% (or
less) of the ricefield and poses no threat to rice production. Chishui and Songtao
Counties have carried out rice-wild rice-fish and rice-lotus-fish experiments.
Production values were CNY3 809/ha in Chishui and CNY4 170/ha in Songtao.15
New Species
Instead of raising only common carp, farmers now raise several fish species. The
temperature of shallow water in ricefields changes with air temperature and is
unstable. However, during the warm season, leaves of the rice plants shade the
water surface and stabilize the water temperature. This creates a suitable
environment for growing grass carp, common carp, silver carp, variegated carp,
tilapia, and crucian carp.
The ricefield is an artificial ecosystem that abounds with various grasses, weeds,
plankton, and other organisms. If only common carp are grown, these resources
are not fully utilized and yields are not very high. In recent years, several species
have been raised together and the results have been encouraging. This demonstrates
that the ricefield ecosystem is suited for polyculture of fish. Normally, common
carp are raised with grass carp or silver carp, grass carp with tilapia, or common
carp with crucian carp and catfish. Either fry or adult grass carp can be raised.
With the appropriate number of fish, rice seedlings are not eaten by the grass carp.
The fish consume grass and weeds to the benefit of rice growth. For example,
2 250-3 000 grass carp and common carp (in the ratio of 4:6 of 10-cm fish) can be
raised in 1 ha without damage to seedlings. When the fish have grown to 17 cm in
length and are able to eat seedlings, the rice plants are tall enough to avoid
damage. If the grass carp are over 20 cm in length, 450-750 fingerlings can be put
into a 1-ha ricefield. In this case, additional feed (grass) must be provided during
the early stage to keep the grass carp from eating the rice seedlings. If silver carp
and variegated carp are raised, their number should be limited to 5-10% of the
total number of fish raised.
In Huangping County, farmer Yang Zaigui raised fish in a 0.08-ha ricefield. On
12 June 1988, he stocked 49 grass carp fingerlings (8.9 kg), 372 common carp
fingerlings (18.4 kg), and two silver carp fingerlings (0.6 kg). After 105 days, he
harvested 34 grass carp (31.15 kg), 356 common carp (66.9 kg), and two silver
15
In October 1988, USD1 = CNY3.7221 and CADI = CNY3.1889.
34
RICE-FISH CULTURE IN CHINA
carp (1.81 kg). Total net production was 73.05 kg. Yield per hectare was 906.8 kg
fish and 7 875 kg rice.
Species Improvement
Local common carp have been replaced with hybrid common carp. The trend is
toward improved species. Local Gaopo carp has long been raised in Southeast
Guizhou. It is docile, quiet, and usually does not jump. During floods, it does not
panic and swim away. It hides in muddy rice water when disturbed. However, its
quality is deteriorating because of poor selection of brood stock. Parent fish are so
small that their offspring do not develop properly.
In 1985, the Aquatic Products Bureau of Leishan County sampled 50 Gaopo carp.
The heaviest one was 350 g and the smallest 25 g. Five of the fish that weighed
25-95 g were mature. Work by the Aquatic Products Bureau of Luping County
revealed that this fish is sexually mature at approximately 100 g. Results from the
Aquatic Products Bureau of Guiyang City showed that 35 % of the fish with an
average weight of 185 g were sexually mature. This suggests that Gaopo carp have
seriously deteriorated and are maturing at a small size. Since 1980, many localities
like Zunyi, Chishui, Wuchuan, Zheng'an, Jinping, and Tianzhu have worked to
improve carp varieties. While paying attention to the selection and improvement
of local varieties, they have also introduced improved brood fish.
In 1983, the Aquatic Products Bureau of Zunyi Prefecture introduced parent fish
of two common carp varieties, Yuanjiang carp and Wuyuanhese red carp. They
achieved good results when they released the hybrid Heyuan carp from these two
varieties. In 1988, the Aquatic Products Bureau of Luping County compared
improved common carp and local common carp. Growth characteristics were
evaluated by taking five samples at monthly intervals after release. Improved
common carp gained 1.95 g more each day and relative growth was 1.5% higher.
When the improved common carp weighed 520 g each, the local common carp
weighed only 200 g (40% less).
In 1987, the entire province began the systematic improvement of common carp.
In 44 variety improvement sites, 31.4 million fry and 9.8 million fingerlings of
improved common carp were produced. A total of 967 ha of ricefields received this
variety and results were good.
Intensive Cultivation
Intensive cultivation of fish is now replacing extensive cultivation. Extensive
cultivation only uses natural feed; therefore, yields are low. In 1980, the provincial
average yield of fish was 78.3 kg/ha. To achieve high yields, traditional culture
systems must be replaced with intensive culture systems that make full use of the
carrying capacity of the ricefield ecosystem. Farmer Lu Binlun in Danzai County
conducted a comparison trial in 1985. Intensive culture yielded 1242 kg of fish per
hectare or 4.6 times more than extensive cultivation (220.5 kg/ha). In 1983, farmer
Liu Dingzhong of Longquan Township raised fish in a 0.32-ha ricefield using
REVIEW AND OUTLOOK
35
earthworms and maggots as additional feed. He harvested 580 kg fish or
1812 kg/ha. In 1984, farmer Li Xingji in Suiyang County harvested 325.4 kg from
a 0.21-ha field by using wastewater from factories.
Prospects
Guizhou Province is a subtropical area with a humid monsoon climate. It has low
latitudes and high elevation. The temperature is relatively high in winter but low
in summer. The yearly average temperature is between 14°C and 16°C in most
areas. The temperature is above 10°C for 220-240 days a year, and 270 days are
frost-free. Annually, there are about 180 rainy days, 1100 mm of rainfall, and
1200 hours of sunlight. There are many cloudy and rainy days and yearly changes
in light, heat, and water are synchronized. All these conditions are conducive to
growing rice and fish. The longer growth period for fish and the good
overwintering conditions allow a sound farmland ecosystem can be established to
increase the production of rice and fish.
Ricefields in the province cover a total area of 791000 ha, over half (about
400000 ha) of which are low-yielding fields. There are 122 000 ha of winter water
fields. These areas are, to various degrees, poor, barren, highly acidic, sticky,
sandy, muddy, and cool and therefore do not produce high yields of rice. Fish
farming improves the soil and rationally uses the land to produce more rice. Fish
farming is profitable and has the potential to improve the economic situation of
farmers, particularly in mountainous areas.
In 1984, a survey was conducted of 20 farming households in Danzai County that
covered about 1.32 ha of rice-fish farms. The output of fish and rice was valued
at CNY4374/ha, 90% more than rice cultivation alone. Surveys in Danzai and
other counties showed that rice-fish farming increased the output value of ricefields
by CNY817.5/ha.
In the future, rice-fish farming will undoubtedly supply a large portion of the
fisheries production in Guizhou, especially in mountainous areas where there are
large ricefields but few ponds or reservoirs. It is important to develop rice-fish
farming and to establish systems for technology extension and for the production
and supply of improved varieties. Ridge-ditches, box-ditches, manure pits in flat
fields, and other forms of rice-fish farming should be adopted to suit local
conditions. Improvement of the common carp variety must continue. Mixed culture
of species (mainly common carp and grass carp) should be practiced. Intensive
cultivation should replace traditional extensive cultivation, which usually has low
yields with low input. Improved fish-farming techniques should be adopted in a
systematic way to make the best use of ricefield resources and to improve fish
yields.
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Reforming Rice-Fish Culture Technology in the Wuling
Mountains of Eastern Guizhou Province
Chen Guangcheng16
In the past, traditional methods of rice-fish culture were used in the Wuling
Mountains. Because output was very low, several reforms were undertaken to
improve rice-fish culture.
Improving the Environment for Fish
Depending on the type of soil, furrows, wide ditches, or pits were dug to culture
fish in flat ricefields. In cold, muddy, fertile fields, rice-fish culture can be carried
out in furrows and wing ditches. The ridge of the furrow is normally about 26-cm
wide and the ditch about 39-cm wide and 26-33 cm deep. In muddy fields, where
it is difficult to make ridges, wing ditches were introduced. The wing is 2-m wide
and the ditch about 0.8-m wide and 0.5-m deep. This innovation improves soil
structure, light, and temperature and increases rice production.
In 1985, these innovations were tested at 54 sites (13.7 ha). The dry rice yield
averaged 6712 kg/ha (18.% more than in flat fields). Ditches help solve problems
created by shallow water and variations in water temperature in flat fields because
they increase the volume of water by about 100%. In summer, changes in water
temperature are 2-3°C lower than in flat fields. This improves the environment for
the fish. In these tests, average fish yield was 507 kg/ha. In high-yielding fields
that can produce 7 500 kg of rice per hectare, fish production is often 750 kg/ha.
In 1987, a 1.5-ha field averaged 7605 kg of rice and 825 kg of fish (average
weight per fish 0.85 kg).
The farmers are given these instructions to implement the new technology:
To culture fish in afield, dig a pit big enough to make up 5-20% of the
field. The pit should be 1.5-m deep and it should link to the fish ditch.
There is four times more water in this field than in fiat fields. This not only
benefits fish growth, but increases the quantity offish and provides the
convenience of dry fields, where farmers can apply additional fertilizer and
agricultural pesticides.
In terraced fields, a big side ditch is dug in the back ridge. The side ditch
should be 1-m wide and 1-m deep and should be linked to the fish ditch.
This enhances the growth of rice, which benefits from warmth, and the fish,
16
Bureau of Aquatic Products, Tongren Prefecture, Guizhou Province.
38
RICE-FISH CULTURE IN CHINA
which like the water. These changes provide conditions for high yields in
rice-fish culture.
Stocking Large Fingerlings and Late Harvesting
In the past, the fish species were usually breed and cultured by the farmers. Most
of the strains have degenerated. A system of elite breeding has now been
established based on the district and township fish hatcheries (e.g., there are
104 sites in Yinjiang County).
Instead of small fmgerlings, 250-300 large (about 10 cm) fmgerlings are stocked
in the fields. Fingerlings should be stocked before the seedlings are planted (from
February to April). This allows the fish to obtain food when plankton is abundant.
Experience has shown that the same-size fmgerlings stocked before planting rice
seedlings weigh 100 g more than fmgerlings stocked after planting.
Keeping water in the fields when the rice is harvested allows the fish to grow for
an additional 60 days and to increase their weight (to about 150 g). During this
period, the rice that falls into the field and the young rice seedlings that grow from
the roots of the rice are good food for fish.
In February 1987, Li Demin, a farmer in Yundu Township, Jiangkou County, put
200 grass carp and 200 common carp, each about 15-cm long, into a 0.2-ha field.
In May, he put 1 800 small fingerlings into the same field. On 19 October, he
harvested 162 kg of adult fish and 31 kg of fingerlings. The adult fish averaged
0.52 kg and some were as large as 1.6 kg. The average yield was 986 kg of fish
and 6 358 kg of dry rice per hectare.
Polyculture and Intensive Culture
In mountainous areas, the fields are poor and weedy; therefore, a polyculture of
grass carp, common carp, and silver carp is used in the ratio of 3:6:1. From May
to July each year, 15 000 small fmgerlings of grass carp and common carp are
stocked per hectare of field. By November, the fingerlings reach a length of
12-18 cm and the survival rate is 20-30%. Weeding is not necessary in fields
devoted to polyculture.
In intensive culture, a base fertilizer is applied before the fish are stocked into the
fields. From April to May, it is not necessary to feed the fish because they are
small, water temperature is low, and benthos and weeds are plentiful. From June
to September, feed should be applied once a day. After the rice is harvested, the
quantity of feed should be reduced.
Scientific Water Management, Proper Irrigation, and Drainage
The basic principal is to consider the needs of both the rice and the fish. When
fingerlings are stocked before the rice seedlings are planted, the water level should
be maintained to minimize fish deaths. Five to seven days after the rice is planted,
39
REVIEW AND OUTLOOK
Table 1. Oulput and value of rice and fish harvests before and after technical reforms.
Rice (1986)
Rice (1987)
Fish (1987)
Fanners
Location
Area
(ha)
Output Value
(kg) (CNY)
Output Value
(kg) (CNY)
Output
(kg)
Liu
Shu-chen
Tongren
4.4
27056 16234
27571 16543
3286
19717
Yian
Zhu-shen
Yuping
1.5
10545
6327
10605
6363
1175
7050
WuXiu-shu
Songtao
1.3
8360
5016
8740
5244
726
4354
Long
Tian-ci
Songtao
0.8
5350
3210
5670
3420
481
2886
Li De-ming
Jiangkou
0.2
1200
720
1238
743
192
1 155
Huang
Xin-tuan
Tongren
0.2
1260
756
1462
878
160
959
55286 33191
6020
36121
Total
8.4
53771 32263
Value
(CNY)
the water level should be reduced to promote tillering. In a furrow or ridge system,
the water should flood the roots of the rice seedlings. When the rice seedlings
begin to turn green, the water level can be reduced. This will not affect the fish
because they are still small.
A month after rice seedlings are planted, the flat fields should be drained for weed
control. Later, the rice water level should be raised to about 12 cm to control
ineffective tillering of rice and to benefit fish growth. After the rice is harvested,
the water should be raised to over 50 cm for continuous fish culture.
Economic Benefits
These technical reforms have produced economic benefits (Tables 1-3).
Value of Output
In 1986, 8.6 ha of ricefields produced 53 771 kg of dry rice, valued at CNY32 262
(Table 1), or an average of CNY3 840/ha. In 1987, with rice-fish culture, these
fields produced 6020 kg of fish valued at CNY36121 and 55 286 kg of rice valued
at CNY33 171. The total value of production was CNY69 292, or an average of
CNY8249/ha, which was 2.1 times more than in 1986 without fish culture.
Ratio of Investment to Income
In 1987, CNY7567 was invested in rice-fish culture, an increase of CNY5252
from 1986. But in 1987, net income was CNY61725, which was CNY31 778 more
40
RICE-FISH CULTURE IN CHINA
Table 2. Investments (Invest.) and income before and after rice-fish culture (CNY).
1986
Area
(ha)
Total
Net
Income
1987
Invest.
Income
Net
Income
Invest.
Income
4.4
15130
1104
16234
31796
4464
36260
1.5
5869
458
6327
12259
1154
13413
1.3
4610
406
5016
8657
941
9598
0.8
2986
224
3210
5768
520
6288
0.2
650
70
720
1628
270
1898
0.2
703
53
756
1619
218
1837
8.4
29948
2315
32263
61727
7567
69293
Table 3. Achieved value by labour force before and after rice-fish culture (CNY).
1986
Total
1987
Area
(ha)
Net
Income
Investment
Income
Net
Income Investment
4.4
15130
706
21
31796
1170
27.18
Income
1.5
5869
275
21
12259
440
27.86
1.3
4610
228
20
8657
349
24.8
0.8
2986
137
22
5768
227
25.41
0.2
650
27
24
1628
53
30.71
0.2
703
30
23
1619
51
31.74
8.4
29948
1403
21
61726
2290
26.95
than in 1986 (Table 2). The ratio of investment to income from rice-fish culture
was 1:6.
Rate of Return
In 1986, net income was CNY29 947. In total, 1403 workers were employed and
each produced an output value of CNY21.34. In 1987, net income was
CNY61725, which was achieved with 2290 workers; therefore, each produced an
output value of CNY26.95 or CNY5.61 (26%) more (Table 3).
REVIEW AND OUTLOOK
41
Value of Fish
Before the reforms in rice-fish culture, fish from the fields weighed about 100 g
each. Because the species had degenerated, they could only be sold for food for
about CNY2/kg. After the technical reforms, 11780 fish were caught from 8.4 ha
of ricefields. Total weight was 6020 kg, or an average of 0.51 kg/fish. These fish
fetched a price of CNY6/kg; therefore, the commodity value of the fish increased
three times after the technical innovations.
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The Development of Rice-Fish Farming in Chongqing City
Xu Shunzhi17
Rice-fish farming has been conducted for over 1000 years in the city of
Chongqing. For a long time, however, fish yields were poor and unstable because
of extensive cultivation, traditional methods, and a variety of limiting factors.
Advances in science and technology, the development of the fish industry, changes
in the structure of rural industries, and an increase in the commodity market led
people to seek new ways to maximize water resources. They pursued new
productive technologies that changed the traditional system of rice-fish culture and
produced economic, social, and ecological benefits.
The productivity of rice-fish farming in Chongqing has been improved by
engineering installations, new technologies for rice-fish farming, and improved
circulation of nutrients and energy in the water. The contribution of rice-fish
farming to total fish production in the city increased from 2-4% in the 1970s to
29% in 1987. In 1987, rice-fish farming ranked second as a method of fish
production and was conducted on 73300 ha of ricefields that produced
10200 tonnes of fish. New cultivation technologies were practiced on 22250 ha
of the total area and produced 6680 tonnes of fish. Some demonstration fields
produced 3000-4500 kg/ha. Total production from rice-fish farming was valued
at more than CNY50 million.
Rice-Fish Fanning in Chongqing
Chongqing, in eastern Sichuan Province, has a subtropical monsoon climate with
adequate heat and rainfall during the warm season. The average temperature is
17.5°-18.5°C, and there are 1000-1100 mm of rainfall, 320-340 frost-free days,
and 1200-1300 h of sunshine. These conditions are suitable for the cultivation of
fish.
For many years, production from rice-fish farming remained poor and unstable.
Improvements were not made because of political changes, faulty economic
policies, changes in farming systems, primitive cultivation technologies, traditions
that were difficult to change, and damage from natural disasters. The area devoted
to rice-fish farming eventually decreased to less than 4000 ha with a total
production of only 300 tonnes. New cultivation methods that used trenches and
sumps were introduced before the 1980s, but results were limited because the
17
Chongqing Bureau of Agriculture, Animal Husbandry and Fishery,
Chongqing, Sichuan Province.
44
RICE-FISH CULTURE IN CHINA
trenches were small and the pits were shallow. During the hot, dry season,
conflicts between the water requirements for rice and fish could not be solved.
However, recent improvements in the rural-responsibility system, the extension of
rice-fish culture technology and the commodity market, and new economic benefits
have encouraged farmers to develop rice-fish farming. The units responsible for
developing aquatic products advocated, demonstrated, and extended advanced fishculture technology. These efforts contributed to the rapid development and
increased productivity of rice-fish farming in Chongqing (Table 1).
To increase production, a variety of methods were studied and adapted to local
conditions of topography, terrain, water quality and temperature, soil, and
vegetation. The goal was to enhance the growth of both rice and fish and to achieve
bumper harvests of both crops. Gradually, fish culture in ricefields was developed
and promoted through demonstrations and extension, and an increased number of
farmers adopted the new technology. Farmers started to stock fish rather than
depend on natural populations. Ricefields produced multiple, instead of single,
crops. The management and administration systems for fisheries were also
improved.
Cultivation Models of Rice-Fish Farming
In rice-fish farming, both rice and fish live in the same body of water and help
each other by creating a favourable living environment that meets their
physiological needs. Optimum conditions include the correct temperature, proper
quality and depth of water, and appropriate nutrients and feed. The methods of
cultivation must promote stress resistance.
Chongqing is located in the hills and low mountain areas of Sichun Basin where
ricefields are widely distributed and natural conditions vary. Several methods of
rice-fish farming have been established to suit local conditions.
Flat fields (or fish sumps and trenches). Ricefields with good water
resources, irrigation, drainage, and stable water (despite drought or excessive rain)
can be used for fish culture. The height of the ricefield dikes is raised to above
0.5 m and reinforced to prevent collapse and leakage. Bamboo screens are installed
to prevent the fish from escaping through irrigation and drainage holes, which must
be higher than the level of the field. Sumps and trenches are dug before seedlings
are transplanted. Usually, ditches are dug around the edge of the field. If the
ricefield is larger than 0.07 ha, a cross-shaped ditch should be dug in the middle;
if the field is more than 0.3 ha, a ditch in the shape of a double-cross (#) should
be dug. In the lower part of the field where the surface is not smooth, 1-m deep
trenches are scooped out along the water inlet or the cross. The number of trenches
varies according to the size of field. Fish varieties are 70-80% common carp and
crucian carp and 20-30% grass carp. The total stocking rate is 3 000-4 500 fry per
hectare (using the previous years stock). Production is 150-600 kg of fish per
hectare.
REVIEW AND OUTLOOK
45
Table 1. Area and production of rice-fish farming in Chongqing (1980-1987).
1980
1981
1982
1983
1984
1985
1986
1987
Total fish 9730 10845 14275 18845 23540 26560 32745 35321
production (t)
Fish production in
rice fields (t)
Area of rice-fish
culture (ha)
1390
1165
3270 5090
6690
6669
8341 10202
23200 18470 43600 54600 68730 78200 70530 72800
Average production
(kg/ha)
60
63
75
93
97.5
85.5
118.5
139.5
Proportion of the
total production of
freshwater fish (%)
13.3
10.7
22.9
27.6
28.4
25.1
25.5
29.0
Fish ponds. Fishponds are dug in the back edge or a secluded spot in the
ricefield. The size and number of ponds depend on the size of the field. The
bottom of the pond should be at least 1 m lower than the level of the ricefield. A
stone wall is built around the pond to prevent it from collapsing. In ricefields of
more than 0.1 ha, ditches (70-cm wide and 50-cm deep), should be dug to connect
the ponds. Stone breaches between the ponds and ditches hold fish screens and
prevent collapse. A 10-cm pipe is sometimes installed in the pond bottom to
improve drainage and management. The fish varieties stocked include common
carp, crucian carp, and grass carp, in equal proportions. Some silver carp and
tilapia are also stocked. From 1982 to 1985, there were 5 880 ha of fishponds in
Dazu County, Chongqing, with an average production of 547.5 kg/ha.
Fishponds are used mainly in winter water fields and in deep-mud fields and waterlogged fields where rice production is low. The specifications for ditches and banks
should be based on the fertility of the field, the farming system, and the rice
varieties. The ditch is usually about 80 cm wide. The field is normally not
ploughed and the bank is built 7 days before transplanting to a height of 20-25 cm
or 3(MO cm. The field should not be drained dry, the banks should be even, and
the ditches straight and connected. A small bank is built, and a row of seedlings
is transplanted onto this bank. The ridge should be reinforced before the bank is
built to prevent fish from escaping. There should be a fish screen in the irrigation
and drainage holes and the width of the breach should be according to the size and
drainage volume of the field. The time, varieties, and size of the fingerlings should
suit local conditions. Common carp or grass carp are the main species, but some
tilapia are cultivated later in the year. Production is about 600-750 kg/ha.
Semiarid plus pond. This method is suitable for use with semi-late rice.
The height of the dike is increased to 0.6-1 m and the dike is strengthened. A ditch
for flood drainage and an opening are dug and fish screens are installed. About 5%
46
RICE-FISH CULTURE IN CHINA
of the field is used as a fishpond (1-1.5 m deep). Before the seedlings are
transplanted, a ditch (35-cm wide, 25-cm deep) and a bank (25-cm wide) are
constructed. When the seedlings have turned green, the natural feed is
supplemented with prepared feed and 80 common carp, 80 grass carp, 40 silver
carp (6.6-cm fingerlings), crucian carp, and tilapia are stocked. Production can
reach 750-2 250 kg/ha.
Ridge-ditch system. Ridges and ditches are dug, based on the size of the
field, available water resources, sunlight, and wind direction, to bring the edge
effect into full play to increase the rice production. Ridges are 1.1-m wide
(transplanting five rows of seedlings) or 0.8-m wide (transplanting four rows of
seedlings); and ditches are 35 cm wide and 25-35 cm deep. Depending on the size
of the field, one or two horizontal ditches are dug to connect all the ditches and
improve the flow of water. This increases the volume of water for the fish and
improves the capacity of the field to store water. Fish are stocked at
4500-7500/ha as 3-cm fingerlings that include 30-40% grass carp, 50-60%
common carp, and 10% silver carp. Production is 750-1500 kg/ha.
Wide ditch around the field. A 1-m wide ditch in the shape of a cross is
dug around and through the field. Both ridged and flat fields are used. Methods are
similar to other systems. Production is 450-750 kg/ha.
Farming with fish cultivation. This method is also called the seven layers
production of rice-fish cultivation. Sugarcane is grown in the ridges of the field
and rice is transplanted into the field. Wild rice is planted between the rows of
rice, and water chestnuts or water hyacinth are cultivated on the water surface. In
the water, fish are cultured in three layers: silver carp in the upper layer, grass
carp in the middle layer, and common carp or crucian carp in the bottom. Fisheries
engineering is the same as for other methods. This method is based on ecological
principles and achieves a balance between plant growth and fish culture and better
economic benefits (Table 2).
Cost-Benefit Analysis of Rice-Fish Farming
Rice-fish farming is an effective way to make full use of ricefield resources and
to cultivate freshwater fish. It offers remarkable advantages: it does not require the
use of other land and water bodies, it has a short cycle, requires small
capitalization, gives fast results and benefits, is easy to manage and uses simple
technology. It also fully uses the productive potential of water in the ricefields. A
1984 study of rice-fish farming in Chongqing by the Bureau of Agriculture,
Animal Husbandry and Fishery, provided data from 153.4 ha of winter ricefields
in four counties near Chongqing (Table 3).
In 1984, the production of fish was 701 kg/ha and rice 7640 kg/ha. The net
income of rice-fish was better than other cultivation industries. Through
demonstrations and extension, small areas of rice-fish culture were enlarged into
commercial rice-fish farming that incorporated pond cultivation and reservoir
fishery. Rice-fish culture has become an important part of the Chongqing fishery.
47
REVIEW AND OUTLOOK
Table 2. Cost-benefit analysis of combination-growing with fish culture in Yangmingqin,
Rong Chang County. Total area 0.12 ha (1985-1987).
Fish
Rice
Sugarcane
Wild Rice
Total Output
Output
Output
Output
Output
Output
Total Value
Prod Value
Prod Value
Prod Value
Prod Value
Value (CNY/
Year (kg) (CNY) (kg) (CNY) (kg) (CNY) (kg) (CNY) (CNY) ha)
1985*
745 335 290 812
-
-
-
-
1147
9558
1986
764
382
370 1665
500
100
-
-
2147
17892
1987
870
478
450
600
120
500
200
2700
3498 29125
'Production prices (Prod) were calculated on the basis of average prices in Chongqing each
year.
Table 3. Economic benefits of rice-fish in 153.4 ha of winter ricefields in the Chongqing
area (1984).
Counties
Farms
Area
(ha)
Fish
Prod
(kg/ha)
Rice
Prod
(kg/ha)
Gross Income
(rice+fish)
(CNY)'
Net Income
(rice+fish)
(CNY)
Jiangbei
319
38.3
691.7
7950
2675.0
1245.0
Jiangjin
409
47.6
761.3
7869
2284.9
1370.9
Dazu
243
33.8
661.1
7875
1983.3
1190.0
Bishan
233
33.7
665.9
6855
1819.6
1091.8
1204
153.4
701.0
7637.3
2063.9
1238.3
Total
"Prices were calculated on the basis of constant prices of CNY3/kg, CNY0.234/kg for rice,
and 60% of output value for net income per hectare.
Advantages and Limiting Factors
In agriculture, ecological and multiple uses of land should not be overlooked.
Rice-fish cultivation can improve the ecological environment of the field, while
providing economic benefits. It makes good use of water resources in the ricefield,
decreases competitors in the waters, makes reasonable use of fertilizer and
sunlight, and improves the fertility and permeability of soil. It can also inhibit or
eliminate weeds in the field. Rice diseases and insect pests are reduced and fish
wastes are a good manure. Extensive rice-fish cultivation helps prevent floods,
increases the resistance of the rice plant to drought and strengthens the regenerative
ability of the ecological system.
48
RICE-FISH CULTURE IN CHINA
In over a decade, the rapid development and multiple cultivation models of
rice-fish farming have also provided direct benefits to Chongqing:
•
•
•
A suitable natural environment — There are 460,000 ha of ricefields
in Chongqing and about 40% of these can be used for fish culture.
Because Chongqing is the main city on the upper Yangtze River,
there is a growing demand for aquatic products.
Productive technology — Chongqing now has several production
units in aquatic science and technology and in fisheries who are
working to develop rice-fish farming.
Enthusiasm of leaders and farmers — Rice-fish farming is an
aquacultural development project of national importance. Because
bumper harvests in both rice and fish have increased the income of
farmers and stimulated the rural economy, rice-fish farming now
appeals to farmers.
Several factors limit rice-fish culture: naturally occurring floods and droughts and
environmental conditions such as terrain and water temperature and quality.
Anthropogenic factors also limit rice-fish farming: lack of fry and fingerlings, the
need to popularize science and technology through extension, and the difficulty of
changing traditional production methods.
Development of Rice-Fish Farming in Jiangsu Province
Xu Guozhen18
Jiangsu Province is located along the coast of the Yellow Sea and is situated in the
lower reaches of the Yangtze and Huai He rivers. Its mild climate and abundant
rainfall make this region ideal for growing rice and fish. Jiangsu Province has
2.4 million ha of land for rice cultivation and about 670000 ha of water surface for
fish production, which makes it one of the important rice and fish producers in
China. There have been substantial developments in rice-fish farming in Jiangsu
Province and farmers are becoming more familiar with the new practices.
Current Situation
Since 1982, rural economic reforms have spread and the industrial structure has
been readjusted. Rice-fish farming in Jiangsu Province grew rapidly during this
period. In 1983, the area for rice-fish culture was 1000 ha; by 1987, 13 000 ha of
ricefields were devoted to fish farming. The practice was adopted mostly in the
Lixiahe region in North Jiangsu and in the hilly country in the centre of South
Jiangsu.
Most farmers incorporated fish farming with midseason or hybrid rice; a few
rotated rice and fish or cultivated them in succession. Farmers also developed their
own ways of raising fish to suit the local conditions, topography, traditions, and
fish species. These included digging fixed fish pits, connecting ricefields to outfield ditches and ponds, polyculturing different species, breeding summer fry in
ricefields, and cultivating rice with fish and freshwater mussel.
The extension of new farming techniques brought vitality to the development of
rice-fish farming in the whole province and upgraded the level of intensive
farming. The average yield of fresh fish increased from 150 kg/ha in 1984 to
300 kg/ha in 1987. Yields were even higher in some areas. In 1985, 190 ha of
ricefields produced 750 kg of fish per hectare; whereas, in 1986, a similar
demonstration area of 270 ha produced the same yield of fish.
In 1987, high production demonstration farms were established in Funin, Jianhu,
and Hai'an counties. Each farm was 670 ha and produced an average fish yield of
705 kg/ha. From 1984 to 1987, the area for rice-fish culture in the province rose
to 40000 ha with a total commercial fish yield of 1630 tonnes, plus a fry yield of
6140 tonnes that could be used to produce 2 400 tonnes of commercial fish. The
total value of fish production was over CNY100 million.
18
Bureau of Aquatic Products, Nanjing, Jiangsu Province.
50
RICE-FISH CULTURE IN CHINA
However, in comparison with other provinces, rice-fish farming in Jiangsu has
developed slowly. The area for rice-fish culture decreased from about 13000 ha
in 1987 to 6000 ha in 1988. The main reasons for this decrease were:
•
•
•
The high-yielding techniques for rice-fish farming were not
adequately extended or widely adopted, which resulted in poor
management. In rice-fish farming, extra care is needed in pesticide
application and drying of the ricefield because these can adversely
affect fish growth. Other factors that can affect rice growth must
also be considered carefully: fish species, fish size, size of water
body, and the type of ditches and pits. However, in practice, some
farmers found it hard to change their cultivation traditions, found
themselves short of labour at the time of planting and harvesting, or
did not take sufficient care. Because of poor management, highyielding techniques could not be fully applied and this reduced unit
yield.
The actual recovery rate was low. At present, the mechanization
level in grain production is low and irrigation facilities in many
areas are poor. In addition, under the current householdmanagement system, management of a piece of land often involves
several households. This creates difficulties and weakens the ability
of the farmers to deal with natural disasters such as drought or
flood. From 1984 to 1987 only 67-70% of the rice-fish farming
areas were harvested.
Production and extension services were not well organized and there
was a lack of channels to provide farmers with inputs such as fry
and chemical fertilizers. Some farmers could not sell their fry,
which were produced too early to be used to stock ponds and
reservoirs. Furthermore, because reproduction quantity and output
value were low, benefits from fish farming were not significant. At
the current yield level of 300-375 kg/ha, unit income is
CNY1200-1500/ha. A farmer household normally only has up to
0.7 ha for fish farming, which would yield only a few hundred
yuan. This is not attractive, particularly in regions where there are
many other economic options.
Ways to Further Develop Rice-Fish Farming
Introduce Appropriate-Scale Management
Economic benefits from rice-fish farming should be improved. Because the rural
economy is developing rapidly, employment opportunities are increasing and some
farmers opt to leave their land for other undertakings. Improved productivity
allows other farmers to farm larger areas and to produce much more grain. This
new kind of farmer provides the basis for larger-scale management and makes it
possible for farmers to make long-term plans. This, in, turn enhances their ability
to cope with nature-induced difficulties and to mass-produce products, which
improves the supply to city markets. Appropriate-scale management is conducive
REVIEW AND OUTLOOK
51
to specialization and commercialization in the rural economy, brings economic
benefits to farmers, can lead to ecological benefits by improving soil fertility, and
can help reduce pesticide application and pollution.
There are two types of management in fish farming. In one type, specialized
households or individuals raise fish, while individual households plant rice. In this
case, specialized fish-raisers take care of water management and fish farming,
while other farmers plant and manage rice. The fish pits and ditches are dug by the
rice-planters. A village committee takes charge of the general production
arrangement. The income from fish farming is distributed among the fish-raisers,
the rice-planters, and the committee in the proportion of 7:2:1. This system makes
management easy, allows for a large area (10-30 ha) for raising fish, and provides
satisfactory benefits to those concerned. A specialized fish-raiser can earn several
thousand yuan each year.
The second type of management concentrates fish farming and rice growing in a
single household and depends on available labour, mechanization level, and the
farmland arrangement of the household. Generally, the farms cannot be too big
(about 2 ha per household). About 10 tonnes of grain and CNY2000 from fish
farming can be produced each year.
Improve Production Conditions and Facilities
Adequate construction work and facilities are essential not only for fish survival in
ricefields but for bumper harvests of fish and rice. Given the precondition of not
affecting rice yields, the better the construction work, the higher the fish
production. With good construction, conditions it is also easier to resolve the
contradictions between rice growing and fish farming and to tackle natural
difficulties.
Various types of constructions are made for fish farming in different rice-farming
systems. In high-yielding areas of Jiangsu Province, several practices are adopted:
•
•
Farmland is rearranged to expand the fish-farming water surface
and increase fish-carrying capacity while trying to reduce the area
for fish ditches and pits. This can be done by combining in-field
with out-field construction. For example, in-field fish ditches can
be connected to out-field water inlet-outlet ditches, natural pits, and
ditches beside roads and tractor paths. To better use in-field ditches,
multiple uses can be made of ditches and pits in rice and wheat
fields.
Appropriate pits and ditches are made in ricefields. These pits and
ditches should be simple in form and relatively close to each other.
The surface proportions of the pits and ditches are 7:3 or 6:4 and
the pits are 1.2-1.5 m deep; the ditches 0.45-0.06 m deep. This
increases the size of the water body and its fish-carrying capacity.
Normally, pit and ditch surfaces occupy 10% of the ricefield.
52
RICE-FISH CULTURE IN CHINA
•
Fish pits and major ditches are dug in a single operation before rice
is planted. The advantages are: much of the work can be done
during slack seasons in connection with other projects such as
irrigation system construction, road construction, and house
building. This not only saves labour, but also reduces labour
shortages during the busy season. Furthermore, these larger pits can
be used for early season fry and late season fish.
Adopt Comprehensive Measures to Prevent Escape of Fish
The key to better economic benefits from rice-fish farming is to increase the actual
catching rate. Fish escape in several ways: because of floods and overflow of
water, through damaged or poorly placed fish screens, and through holes dug by
rats and eels.
To prevent fish from escaping: dikes should be high enough to keep fish-farming
fields from flooding, ricefields should be well equipped with irrigation and
drainage facilities, fish screens should be firm and durable and be placed
appropriately in water exits and entrances, field ridges should be 0.4-0.6 m high
and not leak, and strict management should be practiced to ensure that prompt
action can be taken when problems arise.
Adopt Intensive Farming Measures
Technical guidelines for high-yielding rice-fish farming need to be developed and
promoted using some of the experiences gained from pond-fish rearing:
•
Fish species adapted to the specific needs of different areas must be
selected and used. In Jiangsu, several options could be considered.
Farmers with large areas of water and large numbers of fingerlings
can: mainly breed fingerlings of grass carp and common carp, and
aim for a fingerling yield of 600 kg/ha; or mainly breed fingerlings
of grass carp and common carp, plus 1-year-old fingerlings of a
fast-growing species (e.g., tilapia or hybrid common carp). The
target yield for fingerling and commercial fish is 750 kg/ha. When
the area for fish breeding is small, when breeding is for producing
commercial fish, or when there is no temporary pond for
fingerlings, farmers can: mainly breed Megdobrama ambtycephala,
plus a small number of fingerlings (yield could reach 750 kg/ha);
or mainly breed mature carp with a target yield of 750 kg/ha. Fish
growth should be enhanced with supplemental feeding. To gain
better results, additional weeds, duckweed, and commercial feed are
needed to improve fish growth. Frequent water renewal is also
needed to improve water quality, particularly after land baking and
pesticide application, when the water body for fish is small, and
when organic matter content is high. The added water increases
oxygen, improves feed consumption, and reduces the concentration
of pesticides. Daily field monitoring is also needed to raise the
REVIEW AND OUTLOOK
•
53
survival rate by preventing problems such as pollution, and loss of
fish by escape, theft, of attacks by natural enemies.
Increase the number of species that are raised. Currently, only
commonly bred fish species are raised in ricefields, although some
farmers are exploring ways of breeding specialty aquacultural
products such as clams, shrimp, and mandarin fish. These measures
may help improve economic results; however, the farming
techniques must still be developed and are experimental.
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Rice-Fish Culture and its Macrodevelopment in Ecological
Agriculture
Yang Jintong19
Agricultural production is, in essence, a process of recycling materials and
converting energy. Through this process, the natural functions of animals, plants,
and microorganisms are applied to produce food and other basic necessities. There
are two major trends in the development of contemporary science and technology:
toward in-depth analysis and specialization, and toward integration, which is
broader but less specialized. Integrated development of agriculture and food
production is an important strategy that makes full use of agricultural resources and
promotes the rational development of the agricultural ecosystem.
Experiments and experiences have repeatedly shown that adding fish to the ricefield
ecology helps increase production and achieves social, economic, and ecological
benefits. Rice-fish farming is, therefore, a primary option when trying to develop
ecological agriculture.
Benefits of Rice-Fish Fanning
Nonbiological factors (e.g., water, soil, light, heat, and air) and biological factors
(e.g., animals, plants, and microorganisms) are interrelated and interdependent.
They form an ecosystem with unilateral functions. When one factor changes, it
triggers a chain of reactions. According to the principles of ecology, the structure
of the food chain in a system has a direct impact on the net output of the
ecosystem.
The farmland ecosystem is an anthropogenic system that is regulated to increase its
output. In the biological community of the ricefield ecosystem, rice is
predominant; weeds, plankton, humus, and photosynthesizing bacteria are the
primary producers and the raw materials used by the secondary and tertiary
producers. Rice and these primary producers undertake energy conversion and
storage in a similar manner. They absorb a large amount of solar energy, carbon
dioxide, and nutrients from water and soil to manufacture organic matter by
photosynthesis, and they convert, transport, and store energy. When rice looses
nutrients because of competition among the biological communities, this degrades
the growing environment and increases factors that are unfavourable to growth.
Weeds and large losses of bacteria and plankton through water movement waste
nutrients and solar energy.
19
Aquatic Production Technology Popularization Station, Changsha, Hunan
Province.
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RICE-FISH CULTURE IN CHINA
However, if fish, especially herbivorous and omnivorous fish, are introduced into
the ricefields, they add a new link to the food chain. They feed on the primary
producers and therefore reduce energy losses and improve the use of photosynthetic
products. Fish culture yields products, which can be consumed by humans, and
promotes transformations in the ricefield ecosystem that increase the carrying
capacity of the ricefield. Rice-fish mutualism is the best way to maximize the
output of the ecological system, improve its functions, and reduce the loss of
materials and energy. It is one of the most important natural ecosystems.
Mutualism of Rice and Fish
In the rice-fish ecosystem, rice and fish play the lead roles. Some of their
ecological requirements are similar and this provides the basis for their
synchronized growth. Fish are poikilothermic aquatic animals; rice plants are
thermophilic and semiaquatic. Although each grows and multiplies in its own way,
they have identical characteristics in relation to water. Water is a prerequisite for
raising fish and is also important for the growth and development of rice. Water,
as a component of plant cytoplasm, is indispensable for the synthesis of organic
matter in plants and for the absorption and transfer of nutrients. Water is also a raw
material in many metabolic processes. The amount and quality of water are also
key factors in the survival and growth of fish. Both rice and fish need water. That
is their common characteristic.
The relations between water, rice, and fish must be handled correctly by
controlling water (through ditches or outlets), while satisfying the water needs of
different growth stages of rice (proper irrigation and water discharge). Rice needs
water about 2.5-cm deep during the nursing stage, about 5-cm deep in the booting
and earing stages, and about 6-cm deep in the milk and dough stages. Fish,
especially grass carp, which are adaptable to shallow waters, needs the same depth
of water as rice. Therefore, it is possible to balance the water supply for both rice
and fish by digging ditches or pits.
Because rice and fish also grow in the same temperature range, they can be grown
in a synchronized manner. For example, temperatures above 10°C are suitable for
the growing period of rice, temperatures above 15°C suit the active growing
period, and 21-25°C is the optimum temperature for rice, especially during the
ripening period. If the daily average temperature is lower than 11 °C and lasts for
three consecutive days in spring, early rice may rot. If the temperature in May is
low, if there is a cold moist wind in autumn, or if the daily mean temperature is
lower than 20°C, tillering of early rice and booting of late rice may be affected.
If the daily mean temperature in summer exceeds 30 °C and the highest temperature
exceeds 35°C, the earing of middle rice may be harmed and ripening may be
premature. Hybrid late rice is seedless if the temperature is above 38°C for five
consecutive days. The optimum temperature range for common carp and crucian
carp is 14-18°C; the range for grass carp, silver carp, and Beijing bream is
18-20°C. The temperature range 26-32°C is the peak feeding period. When the
temperature goes over 38°C or drops to below 11°C, fish loose their appetite.
When the temperature drops to about 4°C, fish go into a dormant state, although
REVIEW AND OUTLOOK
57
they can still survive. The optimum temperature for the tropical nile tilapia is
27-28°C and its critical temperature for survival is 10-38°C. Growth is inhibited
when the temperature reaches 38°C, and temperatures below 10°C are lethal for
tilapia.
Ecoagriculture
Ecoagriculture should not be assessed only in terms of grain output; quality, total
biological output, and profits should also be considered. A highly efficient and
rational agricultural ecosystem is ecologically balanced. There should be a balance
between tilling and nursing and between input and output. There should also be
unity in economic and ecological objectives.
In the artificial rice-fish mutualistic ecosystem, green plants are the primary
producers that convert solar energy into the food energy the fish require for their
survival. The sequential relationship in the distribution of rice and fish is apparent.
A study of the ecology of fish in ricefields shows that fish feed on plankton (that
compete with rice for fertilizer), insects and bacteria (that harm rice plants), and
mosquito larvae (that are harmful to humans). Fish assimilate only 3% of these
feeds and discharge the rest into the ricefield. When they swim in the water, fish
release carbon dioxide and this increases the amount of carbon available to the
plants. They also break the soil surface and oxidize layers of soil, which increases
the supply of oxygen and promotes root growth.
Rice-fish culture increases the output of rice by more than 10% (range 8-47%).
It is necessary to establish that rice is most important in rice-fish ecoagriculture to
fully exploit its benefits, avoid harmful effects, and strive for maximum output
using the least possible energy and materials. Recent improvements in rice strains
and crop systems have produced great advances in rice-fish technology. For
example, the raising of grass carp fry in late ricefields can yield 150000 fry/ha in
about 25 days, while improving the fertility of the field.
The new technique of combining ditches and small ponds in ricefields raises the
temperature of the mud and water and aerates the soil. The technique may help
improve cold water low-yielding fields shadowed by hills and prevent drought in
fields on the sunny side of the hill. A rational layout of ditches and small pools also
reduces the concentration of mosquitoes in the centre of the field, which reduces
the number of mosquito larvae and improves health conditions in rural areas.
Grass carp raised in double-cropping fields not only eliminate some pests of rice,
they also feed on and digest the nucleus of the bacteria that causes sheath and culm
blight. Fish excrement does not inhibit the growth of the bacteria's nucleus, but it
does retard the growth and activity of the cell walls of the bacteria. Grass carp may
be an effective way to prevent sheath and culm blight from spreading in ricefields.
High ridges and low furrows turn horizontal production into vertical development.
This helps improve the gley horizon of ricefield soil and expands the ploughed
zone, which, in turn, promotes the growth of plants in the border rows and
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RICE-FISH CULTURE IN CHINA
stimulates the development of individual rice plants. These developments lead to
economic benefits. Yields of 15 000 kg of rice and 1500 kg of fish per hectare can
be attained. The latest scientific research should be applied to further improve
rice-fish culture techniques and increase production.
New techniques maximize the use of ricefields by combining rice-fish culture with
soil and farmland improvement and environmental protection and by adapting
rice-fish culture to local conditions. The techniques include: planting rice on ridges
and raising fish in furrows in low-lying land, in water-logged ricefields with a gley
horizon, in cold-water fields, and in ricefields near mines; and digging ditches and
small pools in dry, hilly ricefields. In fields where yields are stable despite drought
and waterlogging, farmers should adopt methods such as intercropping, crop
rotation, and the use of the free period during late rice, to increase biological
control of rice pests and the yields of grass carp fry. Operations should be
diversified by growing rice with azolla and fish or by growing rice with fish and
frogs. These options will enhance the fertility of the fields, expand production, and
improve economic results.
Forms of Rice-Fish Culture
Hunan Province is south of the middle reaches of the Yangtze River
(24030'-30008' N). The influence of the monsoon is strong, and there are four
distinct seasons. Hunan has a subtropical humid monsoon climate and an annual
mean temperature of 16-19°C. The lowest temperature suitable for rice and fish
growth spans more than 8 months. There are 270-310 frost-free days,
1300-1800 h of mean solar duration, about 3 months of rain, and 1200-1800 mm
of annual precipitation. Light, heat, and water are concentrated in April-September
each year.
The principal crop in the province is rice, which is grown on 2.8 million ha. Highand intermediate-yielding fields make up 64.7% of the total area. Single-crop rice
(one middle rice or a late rice) is grown on 0.5 million ha, mostly in the western
and southern parts of the province. Based on the distribution of ricefields in the
area, the available resources of light, water, and heat, the current production of
rice and fish, and technical conditions, rice-fish culture can be developed in four
different areas in Hunan.
Western Hunan
The area covers the Western Hunan Autonomous Prefecture, the Huaihua
Prefecture, Cili, Taoyuan, and other hilly counties with high altitudes and terraced
and sloping land that lacks the ability to conserve water and fertility and to resist
drought. The southwestern part of the area is warm; the north is cool, humid, and
foggy. Annual mean temperature is 15.8-16.8°C, 1-3 degrees lower than in other
areas of the province. Annual solar duration is 1300-1500 h, which is less than
in northern Hunan. Annual precipitation is 1300-1500 mm, one of the lowest in
the province, but with 330-550 mm of rain in July-September, it has the wettest
summers.
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59
Ricefields take up a large portion of the arable land; most ricefields are hill-shadow
fields, cold-water fields, and winter-ponding fields. The time for raising fish is
long. Because there are few ponds and reservoirs, the area depends mainly on
rice-fish culture for its supply of fish. The area has a long history of rice-fish
farming. In the past, people raised mainly common carp by collecting locally
available fish eggs and hatching them. These operations were extensive and the
variety of fish was limited; therefore, catch per unit was low.
Fish production in ricefields could be increased by improving production
conditions in middle ricefields, adding irrigation facilities and fertilizer, improving
fish-raising techniques, and developing more varieties of fish. Fry should be
hatched outside the fields, seeded in summer, and raised in small ponds in or
outside the ricefields. Farmers should also be encouraged to seed bigger fry,
mostly common carp mixed with some grass carp, crucian carp, and tilapia.
Southern Hunan
The area covers Hengyang City and Chengzhou and Lingling Prefectures. It has
an abundant supply of heat and leads the province in degree days, with
5 300-5 600°C and an average daily mean temperature of 10°C. The annual mean
temperature is 17.5-18°C, the lowest average temperature is 14°C in March, and
the mean temperature in mid-October is 16.5-19°C, Annual precipitation is
1300-1500 mm, with about 200 mm falling in July-September. The rainy season
ends in July, 10-15 days earlier than other areas of the province.
Conditions are favourable for rice-fish farming, especially in spring. The area has
abundant sunlight, an annual solar duration of 1600 h, and 193-195 days with
temperatures above 15°C. This provides ample time for fish growth and
encouraging results have been obtained with fish raised in winter-ponding fields.
The soil in the ricefields is mostly fertile tidal sand mud and black river mud.
Historically, the area practices double-cropping. (The double-cropping system of
planting soybean with hybrid rice in spring was recently introduced and proved to
be a great success.) However, low-yielding fields account for a third of the total
ricefields, and there are also some gley horizon ricefields in valleys and lowlands
where the soil particles are dispersed and marshy. A soil-amelioration plan should
be developed to transform the soil by opening up drainage ditches and flood
diversion channels and canals to direct mountain floods and toxic wastewaters from
mines away from the fields and underground water. Cold run-off water and water
high in iron content should also be drained from the fields. Low-yielding ricefields
could be improved if fish were raised in combination with the rice.
In the Hengyang Basin, fish culture in ponds and pools is flourishing and is wellknown throughout the province. There are ample sources of fish fry and many fish
varieties. Local people collect fish fry along the Xiangjiang River and raise the fry
themselves. To take advantage of favourable conditions, the culture of diverse
varieties of fish in ricefields should be encouraged. At the same time, fish culture
in ponds should be continued. The terrain and weather conditions are variable,
60
RICE-FISH CULTURE IN CHINA
which is favourable for raising fish. A variety of rice-fish culture techniques,
including fish-seedling-rice, rice-seedling-fish, seedling-rice-fish, fish-riceseedling, and fish-rice-fish should be adopted.
In the immediate future, more grass carp varieties should be cultivated in the
wheat-rice fields to ensure the supply of fry for intensive pond culture. Fish
production, from egg collection to the culture of adult fish, should be streamlined
by combining the practice of fish-raising in small pools with rice-fish culture, and
by combining rice-fish farming with pond culture. To expand the area of surface
water and to produce fry on a commercial scale, it will be important to cultivate
fry in ricefields.
In areas where farmers grow early ripening varieties of late rice and plant grass to
raise common carp, the area for rice-fish culture should be expanded by raising
mainly common carp and some other varieties. In winter-ponding fields where fish
are raised, more feed and fertilizer should be applied and a mixture of species
should be used to develop intensive fish culture within one season. In Ningyuan,
Jiangyong, Daoxian, and Lanshan where tilapia can over-winter, fish varieties
should be improved and more nile tilapia should be raised.
Central and Eastern Hunan
The area covers Pingjiang, Liuyang, Changsha, Wangcheng, Ningxiang, Chaling,
Youxian, Liling, Junxian, Xiangtan, Shuangfeng, Lianyuan, Xinhua, Xinshao,
Shaodong, Shaoyang, Longhui, Dongkou, Wugang, Suining, Chengbu, and
Anhua. Water and heat are abundant and increase gradually from the northwest to
the southeast. Annual solar duration is 1500-1740 h. Precipitation in the Dongting
Lake area alone is 1300-1500 mm annually, and 170-190 mm fall in
August-September. The lowest rainfall is in autumn. Most of the ricefields are
distributed between hills and the soil is a red clay. The main cropping system is
double rice plus green manure. Most of the counties in the area raise fish in ponds
and reservoirs.
The area should raise more fish, both fry and adult fish, in ricefields and continue
pond and reservoir culture. Grass carp should be raised in late ricefields and tilapia
should be grown where there are geothermal resources. In areas where rice-fish
farming is practiced, farmers should be encouraged to seed bigger fry, raise adult
fish, and expand the area devoted to rice-fish cultivation. At the same time, efforts
should be made to popularize and improve fish-raising techniques.
Lakeside Rice-Fish Culture Area
The area covers Huarong, Nanxian, Anxiang, Lixian, Changde, Hanshou,
Yuanjiang, Yiyang, Xiangyin, Miluo, Linxiang, Yueyang City (county), Jinshi,
and provincial farms and fish farms. With its alluvial plains, abundant water
resources, and fertile soil, this area is the centre for commodity grain production.
Double rice crops are grown on 92% of the land and green manure on 80%. There
is plenty of gley horizon soil. In some open expanses or plains, surface water often
REVIEW AND OUTLOOK
61
accumulates and a layer of green mud appears near the plow base. In some places,
the soil is submerged in water all year round, and the soil particles are dispersed,
muddy, and marshy.
There are vast expanses of water that are often interconnected. The area is one of
the most important ten freshwater fish areas in China. There are about 170000 ha
of exploitable water surface in the area (50% of the provincial total), but fry are
in short supply.
Weather conditions are good, with abundant sunshine and heat, but less rainfall.
Spring comes late and autumn sets in early. Solar duration is 1700-1800 h
annually, the longest in the province. Annual mean temperature is 16.3-17°C and
annual precipitation is 1200-1500 mm. Precipitation is concentrated in
April-September, which account for about 800-1000 mm (67% of the annual
total). Because summer is late, early rice often ceases to sprout because of low
temperatures in May. The first day when the daily mean temperature is 12 °C about
5 April, and the last day when the mean temperature is 20°C is about
25 September.
To match the mode of production to the lakeside ecology and economic conditions,
the area should concentrate on improving the soil, transforming low-yielding land,
and raising fish in ricefields by introducing the method of growing rice on ridges
and raising fish in furrows. At the same time, efforts are needed to develop sources
of grass carp fry. Technically, several points require attention:
•
•
•
•
•
Breeding and selection should be intensified to advance the artificial
breeding of grass carp to the end of April to match the seasons for
rice and fish production. This would overcome the need to keep rice
in the field to let the fish grow and would improve land use.
Methods of raising fish in both ponds and ricefields and of hatching
fry outside the fields should be introduced. This would mean that
fry could be seeded before the early rice seedlings begin to turn
green, and the fish would have enough time to grow and eat weeds.
It is advisable to raise fish in ricefields with plain open areas and
good drainage and irrigation systems. Flood-diversion ditches,
water-directing canals, and round-the-field drainage ditches are
needed to prevent floods and waterlogging and to prevent fish from
escaping with the irrigation water.
To stimulate rice production by raising fish, fertilizer should be
properly applied in gley horizon ricefields. More phosphate and
potash fertilizer should be applied according to the characteristics
of the soil to improve the quality of crop cultivation. Muddy fields
should be plowed less and extensively worked. Ridge culture should
be adopted in marshy fields to breed strong, sturdy seedlings.
Resistant rice varieties should be planted to increase output.
In water-logged areas in which rice output is low, the soil should be
dug deeply, ridges should be built, and fish should be raised in
ditches and pools. Mulberry trees and hemp can be planted on the
62
RICE-FISH CULTURE IN CHINA
banks. Sericulture can be undertaken, silkworm excrement fed to
the fish, and fish dung used to fertilize the soil. The mud from the
pools or ditches can be used to fertilize the soil in which the
mulberry and hemp are grown, and the hemp leaves can help
preserve water. The cycle provides economic and ecological
benefits.
Value of the Rice-Fish Production in High-Yielding Areas
of Yuyao City, Zhejiang Province
Cao Zenghao20
In Yuyao City, Zhejiang Province, rice-fish farming was developed in the 1950s
at scientific institutions, state farms, and some fishery villages. However, because
of changes in production relations and farming systems, rice-fish farming soon
stagnated. In 1978, it was revived.
Experience has shown that integrated rice-fish production offers economic, social,
and ecological benefits. It has become an important way to increase the income of
grain-producing households, diversify single-product economies in rural areas, and
supply animal protein to improve the nutrition of the people. There are new
problems. Rice-fish farming is limited in high-yielding ricefields where labour is
limited, where arable land is limited and highly productive, where there are a large
number of households that work the land part-time, and where township enterprises
are well-developed. However, these contradictions can be mitigated by research
and field trials to develop rice-fish farming techniques to produce high yields of
rice and fish.
Benefits of Rice-Fish Culture
Recent multilocation trials, demonstrations, and extension efforts in Yuyao City
have shown that major benefits can be derived from integrated rice-fish production
systems.
Efficient Use of Natural Resources
Yuyao City in the southeast coast (29.39°N, 120°E) has an accumulated
temperature of 5073°C, 210 frost-free days, and abundant precipitation and
sunlight. It is a high-yielding area that produces a double crop of rice
(10-11 tonnes/ha of early and late rice). These temperature, sunlight, and
meteorological conditions are also suited to fish culture. In a 1986 study of
107 lowland rice-farming households in Changlou township, fish were cultured in
21.1 ha of ricefields. The output was 6400 kg/ha of early rice and 5 260 kg/ha of
late rice, which was the same output produced in ricefields without fish culture.
Adult fish were cultured in 6 ha with an output of 926 kg/ha. Production reached
11250 kg of rice and 750 kg of fish per hectare, and the value of the output was
doubled. Another 15.1 ha were used to produce 499 kg of fingerlings per hectare.
20
Yuyao Aquatic Product Bureau, Yuyao City, Zhejiang Province.
64
RICE-FISH CULTURE IN CHINA
Farmer Yang Tiexian dug ditches in 11% of his 0.18-ha ricefield to breed
120 grass carp, 1000 bream, 750 crucian carp, and 5 000 adult carp in early
spring. By 10-15 October, he harvested 703 kg (3 905 kg/ha) of rice and 100 kg
(558 kg/ha) of fish. His experiments were verified by researchers from both
Ningbo and Yuyao.
This example illustrates that pits and ditches for fish culture can enhance the
growing environment for both rice and fish and can increase economic efficiency.
Organic matter in the water (e.g., plankton, benthos, insects, weeds, and
organisms harmful to rice) serve as fish food. The movements of the fish stir the
water and loosen the soil to improve oxygenation and soil fertility. Fish feces are
quality organic manure for rice.
Intensification of Agriculture
Farmers in Yuyao City only have about 0.05 ha of ricefields each. The multiplecropping index has reached 240% and the population continues to grow rapidly.
The amount of arable land limits agricultural production. For this reason,
agricultural production must be diversified and farming must be intensified to
obtain maximum economic, social, and ecological benefits. Rice-fish farming is
an effective way to increase productivity when farmland is limited.
Farmer Jin Wanshun and his family contracted 1 ha of ricefields. Since 1984, he
has managed this farm using an integrated method that includes growing rice, fish,
fruit, and vegetables. In 1987, he implemented the rice-fish system and planting
grapes and vegetables on the ridges of 0.7 ha of ricefields. He harvested
12335 kg/ha of rice and 1061 kg/ha of fish. His family sold 5200 kg of
commodity grains, 440 kg of live fish, and 150 kg of fingerlings. Calculated on the
basis of local prices, his family earned CNY2 514 from rice, CNY3 305 from fish,
CNY1000 from melons and vegetables, and CNY4000 from household sideline
products. Of the total income of CNY10500, rice-fish farming contributed 30%
to total income and 46% of agricultural income.
Integrated rice-fish production plays an important role in the development of a
diversified economy. Its economic benefits are double those obtained in
monoculture under the same conditions.
Creation of a Favourable Ecological Environment
At present, increased crop yields depend on the application of a large amount of
fertilizer. These fertilizers have increased energy consumption and production costs
and polluted the environment. In the rice-azolla-fish ecosystem, azolla is a
fertilizer and food for the fish. Fish eat insects and weeds, and their feces fertilize
the rice plants. This reduces the need to apply chemicals because pests and diseases
are minimized and soil fertility is improved.
In Chang Feng Township in 1985, farmer Chen Bingcan and his family contracted
2.3 ha of farmland. They used the rice-fish system and grew rice with azolla in the
REVIEW AND OUTLOOK
65
spring and fish in the summer and autumn. After 3 years, soil fertility had greatly
improved. The Institute of Soil and Fertilizer, Zhejiang Academy of Agricultural
Sciences, determined that the organic matter content of the soil had increased from
2.9% to 3.3% and that the nitrogen content had risen from 0.2% to 0.3%. Pest
damage was also reduced, and weeds had been reduced by 56 times. There were
only 27 weeds/m2 in the ricefield with fish and 1521 weeds/m2 in the field without
fish. Sheath blight had declined from 47% to 33%. Rice seedlings were
transplanted into untilled ricefields, which meant that plowing and weeding were
not necessary. The application of fertilizer and agricultural chemicals was reduced
by 40%, which lowered production costs and increased income.
A 1987 survey showed that a 1.7-ha ricefield that used the rice-fish integrated
production system yielded 2 860 kg of hybrid rice seed, 1560 kg of rice grain, and
2 860 kg of live fish. The income was CNY6 240/ha, or CNY3 820/ha more than
the CNY2420/ha that was obtained from planting rice alone in a 0.4-ha ricefield.
Limiting Factors
Although Yuyao City has favourable temperature, sufficient sunlight, and 2915 ha
of ricefields for rice-fish farming, there are also limiting factors.
Scattered Plots and Extensive Cultivation
Since the implementation of the production responsibility system, most farmers
have only have about 0.2-0.3 ha of arable land. Many have left their farms to
work in township enterprises. The resulting labour shortage has limited the
development of rice-fish production systems.
Limitation of Traditional Cropping Systems
There are contradictions between the management techniques for the traditional
rice-cropping pattern and the rice-fish pattern. For example, when the close
planting pattern (12.5 cm x 12.5 cm x 12.5 cm x 10 cm) is adopted for
transplanted rice, toxic chemicals are applied to prevent pests and diseases and the
field is frequently idle. These chemicals limit rice-fish farming.
Lack of Knowledge of Fish-Culture Techniques
Farmers are experienced in rice farming but lack knowledge about fish culture.
Techniques for breeding fish in ricefields have been developed in recent years, but
farmers need more technical guidance as well as an effective service system and
administration. The supply of fish fry and fingerlings are insufficient. These factors
have constrained the development of the rice-fish production system.
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RICE-FISH CULTURE IN CHINA
Future Needs
Identification of Development Priorities
To boost the commodity economy in the countryside and to improve its efficiency
and benefits, arable land must be gradually centralized by big rice-grain producers
in rural areas. This centralization should be followed by extension information
about rice-fish production systems.
Strengthen Research
The rice-fish production system lacks a model and must be standardized to be
easily adopted by farmers in rice-growing areas. Rice-fish farming techniques
should be disseminated through technical training, demonstrations, and on-farm
visits.
Improve Engineering Facilities
Rice-fish farming facilities must be altered to enhance the symbiotic environment.
Scattered and shallow trenches should be converted to centralized and deep
trenches that make up 6-8% of the total area of the ricefield. The growth of both
rice and fish should be promoted by providing a habitat for fish migration and by
changing from square close planting to wide-row close planting. These changes
will alleviate the contradictions between fertilizer application, water irrigation,
plowing, transplanting, and pest control.
Enhance Cooperation and Service
The rice-fish integrated production system is multidisciplinary and combines
agronomy with the aquatic products industry. To develop fish farming in ricefields,
farmers must be provided with an adequate supply of fish fry and fingerlings,
marketing information, and an effective fishery administration to ensure production
safety.
Developing Rice-Fish Culture in Shallow Waters of Lakes
Wan Qianlin, Li Kangmin, Li Peizhen, Gu Huiying, and Zhou Xin21
Per-unit fish output from lakes, especially large ones, is low in China. Rice-fish
culture increases the yields of both fish and rice; therefore, the potential exists to
invigorate inland fisheries and to increase rice production. Deepwater rice is
adaptable to different water depths and is a stable and natural adjusting and
controlling factor that could help solve the difficult problems involved in the
establishment of large-scale ecological agriculture. Deepwater rice might also
prevent the proliferation of blue algae in East Taihu Lake and lessen the impact of
water pollution and eutrophication caused by population growth and urban and
rural development. Deepwater rice is usually grown in areas that hold water during
floods. Deepwater rice is a major crop in Southeast Asia, but few data are available
on deepwater rice-fish culture in lakes. The feasibility of deepwater rice-fish
culture was studied to observe the growth of deepwater rice in deep ponds and in
shallow lakes and to determine which species of fish might be suitable.
Experiments with Deepwater Rice
Deepwater Rice
Twenty-three varieties of deepwater rice (including two varieties of floating rice)
developed by the International Rice Research Institute (IRRI) and quarantined in
the Philippines were studied. Seeds were dried in the sun, soaked, and germinated
on 18 May 1987. Seedlings were transplanted on 18 June, three to a hill, 25 cm
apart and in rows that were 25 cm apart (variety no. 1 was planted two to a hill).
Some of the seedlings were transplanted to a 60-m2 area in Huayuan Lake that was
10-40 m in depth. On 12 July, the water in the lake rose sharply by 1 m in 12 h,
which submerged the rice plants. The water remained at that level for so long that
all the rice plants drowned.
Fish
Five days after the seedlings were transplanted, 3 200 crossbred fingerlings were
released into a 0.07-ha experimental plot. The fingerlings were bred by the
Freshwater Fisheries Research Centre of the Chinese Academy of Aquatic
Products. There were 1000 crosses between Cyprinus carpio Wuyuanensis and
C. carpio Yuankiang (averaging 2 cm in length) and between Oreochromis aurea
and O. niloticus (averaging 1-2 cm in length). As well, crucian carp (crosses
21
Freshwater Fisheries Research Centre, Chinese Academy of Fisheries
Science, Wuxi, Jiangsu Province.
68
RICE-FISH CULTURE IN CHINA
between Carassius auratus Gibelio (Bloch) and Carassius curierit, (averaging 4 cm
in length) came from the Wuxi Aquatic Products Breeding Farm in Jiangsu
Province. The fish were caught on 6-7 November. The length and weight of some
of the fish were recorded. Others were released into an aluminum tub (without feed
or changes in water) to test their physical ability to withstand adversity.
Experimental Sites
Experiments were conducted simultaneously in Wuxi and in Anhui Province. In
Wuxi, deep open pits were rebuilt with clay into two experimental plots (pH 8).
An adjacent stream served as the water source. One plot was 0.07 ha; the other
0.03 ha. Each could hold water more than 1-m deep. Before the rice seedlings
were transplanted, one pit was pumped dry, and 1000 kg of mud were removed
and spread on the bottom of the experimental plot to increase fertility and stabilize
the plants. Then 735 kg of barnyard manure (496 kg pig dung and 240 kg poultry
dung) were added as base manure. After the seedlings were transplanted, 5 kg of
urea were applied as manure to stimulate the rice seedlings to turn green and
another 5 kg of urea, 3 kg of calcium superphosphate, and 5 kg of plant ashes were
added as manure to stimulate booting. Before the autumn equinox, 50 kg of lime
were spread to prevent and control fish diseases. Later, 60 ml of 25% sumithion
dissolved in 60 L of water were sprayed to control stem borer, and 25 g of 50%
thiophnate were applied to control green smut.
It was difficult to raise the water level steadily, but water depth and temperature
were recorded daily, and the heights of 10 rice plants for each rice variety were
measured at random every 10 days. The degree days during the initial booting
stage for 10 varieties and the degree days during the earing stage for two mature
varieties were determined from the mean daily temperature readings issued by the
Wuxi City Weather Station.
On 5 November, before the harvest, varieties 1 and 2 ripened and birds began to
eat the ears of rice. Twelve sample plants were collected at random to record
effective tillering. The 1000-kernel weight and the length of each ear were
recorded for every 20 ears. The earing of each variety was closely scrutinized to
avoid underreporting. Plants were sampled randomly to measure the distribution
of the degree of earing. The Huayuan Lake experimental zone in Anhui is situated
where Fengyang, Jiashan, and Wuhe counties cross on the southern bank of the
lower reaches of the Huai He River. The surface of the lake is 4 000-8 000 ha, the
area where water rises and falls covers more then 1000 ha, and the depth of water
is 1.6-4.9 m. Mean annual water temperature is 17.2°C; during May-September
the water temperature is 18-30°C. Mean air temperature is 14.9°C and there are
212 frost-free days. The shallow areas of the lake are broad, with a slope of about
1:20, and the lake is rich in humic substances.
REVIEW AND OUTLOOK
69
Results
Growth of Fish
A total of 1264 fish were caught (average 300 kg/ha), and the overall survival rate
was 39%.
Common carp (Cyprinus carpio). The first catch netted 246 fish weighing
a total of 2.89 kg, with a survival rate of 24.6%. Body length ranged from 6.9 to
23 cm (a difference of more than three times) and weight ranged from 6.5 to 264 g
(a difference of 40.6 times). The fish seemed physically strong; 30-40 days into
the experiment, and they were still active.
Crucian carp (Carassius carassius). The first catch netted 682 fish
weighing a total of 9.23 kg. Survival rate was 56%. Body length was 9.5-12.4 cm,
and weight 10-24 g. The average weight ranged from 12 g to 15.3 g. Growth was
uniform, and the fish were strong and healthy, except those grown without rice in
the 0.03-ha pond. The smallest and the largest fish withstood adversity-resistance
tests for 43 days and still swam actively (water temperature was 7.3°C).
Tilapia (Oreochromis spp.). The first catch netted 336 fish weighing a total
of 7.85 kg. Survival rate was 33.6%. Body length was 9.8-12 cm and weight
14-28 g (70% were 10-11 cm in body length and 19.5-23.5 g in weight). Length
growth was uniform, but because of infertility of the water, body weights were not
uniform. The weight difference among those with 9-cm bodies was as much as 6 g;
among those with 11.4-11.5-cm bodies, the difference was as much as 4.5 g.
Some fish measured 9.5 cm in body length, but weighed only 23.5 g; others
measured 9 cm in body length, but weighed 28 g.
Ripening of the Deepwater Rice
Two varieties ripened and bore fruit: IR40992-1-3-2-1-1-2 865020 (no. 1) and
IR40992-1-3-2-1-3-3 865022 (no. 2). Their productive properties are shown in
Table 1. Part of the grains of variety IR41125-7-3-2-2-3-3 865026 (no. 3) were at
the milk stage and one-third of the plants showed a 100% heading rate. The
varieties that approached the milk stage were IR23426-RR (no. 22) and IR41132R-27-1-1 (no. 4). No. 22 was 50% better than no. 4 in terms of heading, and onethird reached the late heading period (> 80%). No. 4 only approached the middle
and late heading period. Eleven other varieties showed heads, but not on all plants.
The other varieties either just entered the heading stage (e.g., no. 13, 7, and 9) or
showed heads, which disappeared before the harvest (e.g., no. 14 and 20).
The height of 23 varieties (1.4-2.1 m) exceeded previous records. Water depth in
the experimental ponds was usually 40-60 cm, but exceeded 60 cm for one-fourth
to one-third of the days. Booting and earing occurred when the water was
65-80 cm deep. Seven varieties grew in water more than 2-m deep and only no.
15 did not show heads. Two varieties grew in water less than 1.5 m and all showed
heads.
70
RICE-FISH CULTURE IN CHINA
Table 1. Productive properties of two varieties of mature deepwater rice."
Productive Property
Effective tillering (no./plant)
Number of plants/ha
Plant height (cm)
Number of ears/ha
Length of ears (cm)
Variety No. 1
4.9
Variety No. 2
3.9
288 720
432 720
180
185
1423 380
1674 630
24.7
28.7
Number of grains/ear 154.4 196.8
Fertility (%)
65
1000-kernel weight (g)
26.0
Estimated output (kg/ha)
3689
65
26.3
5625
" Plant and row spacing = 25 cm. For variety no. 1, two plants were planted per hill; for
variety no. 2, three plants were planted per hill. Fishways occupied 10% of the surface area
of the water.
In either case, the highest and the lowest, there were varieties that showed heads
in large tracts: no. 4 plant was 2.0-m high, and no. 22 was 1.4-m high. The stage
of heading in the 1.8-m high mature varieties varied: some of the plants of variety
no. 3 were in the milk stage, no. 9 and 7 showed heads to varying degrees, and
two varieties did not show heads. Ears in floating varieties (no. 8 and 17), which
were 1.9-m and 1.7-m high, respectively, were rare.
Prevention and Control of Pests
Fish, rice, frogs, and spiders lived together in the ponds. The experiment explored
ways of combining the use of pesticides with biological methods of pest control.
Pests. Rice plants infested by stem borer had the symptom of white ears.
Although road lamps on the side of the ponds attracted some borers, it was difficult
to kill all of them. Where the stem borer invaded, the ear stem was higher than the
water surface. The depth of water (^50-60 cm during the earing stage) was far
from being completely used by the fish. Furthermore, pesticides were not very
effective. It is advisable to apply pesticides before stem borers invade the ear stem.
Plant disease. Green smut infested the rice in spots, often on ripened rice,
but the spread was limited.
Birds. There were no ricefields around the experimental plots and flocks
of birds were spotted only in nearby woods. No birds were seen feeding on the rice
REVIEW AND OUTLOOK
71
during the ripening stage until three short-grained rice plants on the edge of the
plot were eaten off.
Growth of Deepwater Rice
Growth and survival rates of rice in Huayan Lake in water 10-cm deep were better
than in water over 25-cm deep. Seedling growth was not apparent during the first
few days after transplanting. New shoots were not visible until a week later; then
growth was 1.0-1.5 cm/day and, after the tenth day, about 2 cm/day. When the
rice plants had grown to 45 cm, they were already submerged in water. Seedlings
3 cm above the water survived and grew well if the water did not submerge a third
or half of the plant. Twelve hours after transplanting, one or two new roots were
visible; these proliferated after a week. Although the seedlings were placed in a dry
place for more than 30 h before transplanting, survival rate was 85%.
Discussion
Of the 23 varieties improved by IRRI, only seven (30.4%) showed unripened ears
and 16 (69.6%) showed apparent heading. Except for a few which showed booting,
most had more than 50% of heads showing. The booting stage of 10 varieties
lasted 39 days (21 August - 29 September). During the 32 days starting from
28 August, full heading was seen in some plants and large tracts of heads were
seen in some varieties. But from 29 August to 3 September, only varieties no. 1
and 2 showed mature heads (hard doughed ears). The booting stage for no. 22, 3,
and 4, which showed no milking or did not fully mature (hollow or immature
ears), started in mid- and late-September. This was related to the low temperature
(<20°C) at the time. Varieties no. 7 and 14 entered the booting stage a week
earlier than no. 1 and 2, but mature ears were rare and heads were found on less
than 80% of the plants. This may have been caused by high temperatures (> 35 °C)
for 3 days in mid-August, which affected follow-up growth.
In other immature varieties, analysis of the distribution of the number of heads
showing revealed that some were affected by degree days. For example, varieties
no. 9, 7, 13, and 3 showed a large difference in degree days, with the range of
difference decreasing from large to small (81%, 76%, and 39%). The plants
needed more degree days. Some had immature ears. Variety no. 6 had a head
showing of 65-97%; whereas, no. 22 had 53-86%. Variety no. 22 entered the
booting stage 10 days later than no. 6, but it was able to reach the earing stage in
large expanses and mature more quickly than no. 6. The booting period does not
necessarily determine the maturity of ears. Varieties 6 and 13 entered the booting
stage on the same day, but the head showing of no. 13 was no more than 39%,
which was lower than the lowest (65%) of no. 6. If no. 6 had been transplanted
earlier, it might have shown the same general maturity as no. 2.
Pool Experiment
On 1 July, 12 days after transplanting, and when the plants were less than 50-cm
high, the water rose nearly 30 cm in one week. After that, the water level rose and
72
RICE-FISH CULTURE IN CHINA
fell alternately until 1 August when it was nearly 60-cm deep on two occasions. It
dropped to about 40 cm 43 days after transplanting, and most plants were more
than 100-cm high. Therefore, the plants could withstand the water when it rose
later to more than 60 cm. During this period of nearly one month, plant growth
experienced two cycles, one from fast to slow (50-60 days after transplanting and
at 70-80 days), the other from slow to fast (60-70 days after transplanting and at
80-90 days), that corresponded to the rise and fall of the water level. This shows
that the water level had some impact on the growth of the rice plants. When a plant
is about 50-cm high, it can resist submergence; as the water rises, the plant is able
to continue to grow. Before Huayuan Lake was flooded, the plants were 45-cm tall
and had already acquired the ability to survive submergence. However, if the water
had risen too fast and too high, the plants would have died. They would not have
been able to grow quickly enough to rise with the water level.
The deepwater-rice seedlings showed new roots less than 12 h after transplanting.
It may be possible to replace transplanting with a new planting method that exploits
the rapid root development of seedlings. When the seedlings turned green, the root
system began to proliferate. After 10 days, plant growth doubled. The fertile soil
in the lake, the density of transplanted seedlings and their accelerated growth
during the later stages, built up their capacity to resist flooding. Because the water
was shallow, the plants could have drooped as they grew taller, but they withstood
the sharp rise in flood water without damage. However, it is important to prevent
the plants from being submerged until they have grown tall. A certain time is
needed between the growth of the rice plants and flooding.
Although the common carp grew unevenly, those in the experimental plots had
reached a fairly high level of growth. In the comparative ponds where fish grew
in a natural environment, maximum weight was 169 g, with 19 cm body length and
23 cm total length. The corresponding common carp (18.5 cm, 22.6 cm) grown
in experimental plots with deepwater rice, weighed 191 g. The largest was 264 g,
with 23-cm body length and 27 cm head-to-tail length. There were apparent
differences between the least-developed common carp in the two ponds (5.7-cm in
body length and 6.8-8.0 cm in head-to-tail length). Before the fish were caught,
living organisms (144/m2) at the bottom of the lake were collected (weight 96.2 g).
These included annelids, mosquito larvae and silk earthworms, and tulip shells
(data collected by Mr Chen Wenhai). Because rice was planted, the bottom
organisms had a rich supply of food. But because the pond leaked, water had to be
constantly replenished, which reduced the level of fertilization. This change
corresponded to good growth of bottom-living common carp and crucian cap, and
poor growth of tilapia.
Rice planted in a shallow lake increases the productive surface area, oxygen, and
food. These factors promote the growth of common carp. Because the volume of
water is greater than in rice paddies, it is suitable for raising marketable common
carp. Crossbred crucian carp, like the silver crucian carp in Northeast China, are
large (up to 3 kg each), and when combined with the planting of deepwater rice,
will help raise the harvest. The planting of deepwater rice will help create
conditions that will turn lakes into highly efficient fishery bases for a variety of fish
REVIEW AND OUTLOOK
73
species. The shallow waters of lakes provided good fertility, temperature, and
sunshine. The open expanses of water are deep and can hold large numbers of fish.
The development of such resources will help increase fish harvests from lakes.
It is not possible to establish truly comparative conditions in the experimental
ponds; therefore, data are lacking to substantiate the benefits of growing rice and
fish together. The experimental ponds contained more water and received
2-3.4 times more fingerlings than flooded ricefields. The depth of water could not
be kept at 60 cm, and therefore the volume of water per fish was lower than in the
flooded ricefields. Per-unit output remained at about 20 kg, the same level of
production as fish culture in flooded ricefields. Furthermore, the fingerlings were
released late, they were small in size (the survival rate of winter fish may be
higher), and water quality was poor. The fish were not fed in July-August, their
peak growing season. The water levels changed quickly and there were potential
natural enemies. All these factors limited the fish catch and the benefits from
rice-fish cultivation.
Conclusion
Two of the deepwater rice varieties developed by IRRI grew to maturity in the
catchment area of the Yangtze River in the Taihu Lake area. Rice-fish culture in
this area produced 3 750 kg/ha of rice and 350 kg/ha of fish, which indicates there
are prospects for developing rice-fish culture in the shallow waters of lakes.
Although per-unit fish catch in the laboratory was the same as in ricefields, the fish
were strong, and the crucian carp were uniform in size. Common carp were not
uniform in size, but improved fertility at the lake bottom might produce common
carp of a higher quality. The short-term trial production of rice-fish culture in the
shallow waters of Huayuan Lake shows that the growth of rice plants and the
proliferation of new roots is as good as in flooded ricefields. Despite incomplete
results, the comparison of rice and fish production in both enclosed ponds and lake
shallows suggests that rice-fish culture is feasible in shallow areas of lakes.
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Part II:
Patterns and Technology
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Different Methods of Rice-Fish Farming
Nie Dashu and Wang Jianguo22
Many methods of rice-fish farming have been developed in China. Although they
involve various production systems, these different methods are inseparable and
interlinked. The common aim is to boost rice production by eliminating weeds and
pests. Many different types of rotation are practiced.
Rice-Fish Mutualism
Early, middle, and late rice are planted continuously without interruption. Two
kinds of fry (fingerlings and summer fry) are released directly into the flooded
riceflelds. Specific practices include raising fingerlings in flooded ricefields,
raising fish in ricefields and in nearby ponds, planting rice on the ridges while
raising fish in the furrows, and raising fish in ricefields in which channels have
been dug.
Breeding Fry in Riceflelds
To reduce the cost of summer fry, a model has been devised that involves releasing
fry directly into early flooded ricefields. Grass carp (Ctenopharyngodon idella) fry
are generally used, and because feed is not needed, the method is economical.
After middle rice is planted, 1000 fry, 3.3-5 cm in length, can be harvested from
the early ricefields. Because costs are kept to a minimum, it is easy to popularize
the method in areas with large expanses of water. The early rice planting season
(late April) in Hunan, Jiangxi, Anhui, Jiangsu, and Zhejiang coincides with the
production of common carp (Cyprinus carpio) fry. Therefore, after the rice
seedlings have been transplanted, the ditches dug, and the screens installed,
C. carpio fry can be released into the ricefield. The fry are too small to uproot the
seedlings and because this is the peak period for plankton, fry growth is enhanced.
It is best to release the fry as early as possible to take full advantage of this peak
in plankton growth. If the artificial hatching of fry is delayed, the application of
base manure and the transplanting of early rice should also be delayed to maximize
the mutual benefits that can be achieved.
At present, large fish-fry breeding farms have advanced the season of fry hatching
to late April and the rice growers on these farms delay the transplanting of rice
seedlings. But the practice has not gained much popularity. Additional effort is
needed to disseminate the idea and launch demonstration projects. For every
22
Institute of Hydrobiology, Academia Sinica, Wuhan, Hubei Province.
78
RICE-FISH CULTURE IN CHINA
hectare of ricefield, 45 000 artificially hatched fry are needed. Along the Yangtze
and Zhujiang Rivers, where people catch river fry, it is better to put these fry into
early ricefields because it makes it easier to regenerate fish of the same family.
Stocking fry, which have just begun to eat, into early ricefields 3-4 days after the
rice is transplanted offers many advantages. It eliminates the need to buy summer
fry, means that ponds are not needed for summer fry, and maximizes the mutual
benefits of growing rice and fish together. It is an economical, practical method
that yields better and faster results.
Ctenopharyngodon idella, with its ability to eliminate weeds and worms, can help
increase rice output and reduce the need for labour. However, in areas with few
ponds or banks, other fish species (e.g., C. carpio, crucian carp, and tilapia) can
be raised. Even in ricefields overgrown with weeds, it is feasible to grow C. idella
along with some C. carpio and C. auratus.
When this method is adopted, the banks of the fields must be raised 50-70 cm and
strengthened before the fry are released into the field. Lime is applied
(375-750 kg/ha) to kill leeches, eels, and other natural enemies of the fish. Six to
eight days later, water is channelled into the field and base manure is applied. The
field is raked level, and the rice seedlings are transplanted. Fish canals and ditches
(30 cm wide and 30 cm deep). Where the canals cross, a fish ditch 100 cm long,
70 cm wide, and 80-100 cm deep is dug. Rice seedlings in the canals should be
transplanted to the edges of the field to from a fence. Screens, each 100 cm wide
and 80-90 cm tall, should be installed in the water inlet and outlet. Each screen
should be arch-shaped with thin bamboo strips placed 0.2 cm apart. Fry may then
be released into the field. Field management should be strengthened. Before the
rice ripens and all the weeds are eaten by the fish, the canals and ditches are
opened and the water is drained slowly to force the fish to gather in the canals. The
fish are then driven into the ditch where they are netted.
This is the best method for raising fingerlings. In Sanming City, Fujian Province,
the area of ricefields for raising fingerlings increased in 1982-1984, from 270 ha
to more than 670 ha, and the number of fingerlings raised increased from 2 to
8 million (62% of the fingerlings raised in the entire city). In addition, rice output
increased by 6-17 %.
The catch of adult C. idella from fishponds has remained low. Because they are
unable to adapt to the environment in fishponds, the fish easily become ill. Usually
only 20-30% survive. In ricefields, on the other hand, the ecological environment
is suitable for C. idella, and few, if any, become ill. This is why the output of
freshwater fish can be doubled.
Rice, Fish, and Azolla
In this method, the raising of C. idella or tilapia in ricefields is organically
combined with the growing of azolla. Rice is grown in the field, azolla on the
surface of the water, and fish in the water. Fish feed on the azolla, and the field
is fertilized by fish excrement. Melons and beans can also be planted on the banks
PATTERNS AND TECHNOLOGY
79
of the field to form a vertical cultivation system. Instead of the conventional equaldistance planting method, rice growers use wide and narrow rows. They raise
azolla and fish in the wide rows and plant rice in the narrow rows. This keeps the
field well ventilated and maximizes the use of sunshine and the effects of edge
rows. As a result, it ensures stable and high yields of rice and fish, good economic
returns, social benefits, and ecological efficiency.
This research was sponsored in recent years by Liu Zhongzhu, President of the
Fujian Academy of Agricultural Sciences. After 3 years of experimentation, the
method is now widely applied in Jianning County, Fujian Province. In 1986, the
county devoted 6670 ha or 46% of its ricefields to this method of farming. The
method generates additional income of CNY2 250-2 700/ha of rice planted, and
rice output can be increased by about 7%. Because there are fewer weeds and pests
in the fields, there is less need to apply chemical fertilizers and pesticides, which
helps reduce costs by about CNY150/ha. The county reported a total fish catch of
1.15 million kg from ricefields in 1985 and 1.5 million kg in 1986. Most of the
fish were sold in the market, which added, on average, CNY20 of income per
household.
Raising Fish in Ricefields with Wide Ditches
This method is used to raise winter fingerlings. Ditches, about 1-m wide and 1-m
deep, are dug on the water inlet side and inside of the field bank. The total area of
the ditches is about 5-10% of the area of the ricefield. The ditch ridge is raised
25 cm above field level. A 24-cm opening every 3-5 m links the ditches with the
field and allows the fish to move freely from the ditches to the field. Long before
the rice-transplanting season, winter fingerlings are put in the ditches so that they
can enter the ricefield for food as soon as the early rice seedlings turn green.
Jiangxi Province devoted 6670-9 330 ha of ricefields to this method in 1985-1986
and reported a 20-50% increase in rice output.
Ricefield Plus Fish Farming in a Pond
In rice-fish farming, there is a time difference of about 1 month between the early
rice and the hatching of summer fingerlings. The rice plants need sunlight,
fertilizer, and pesticides. These conditions are not favourable for fish farming. In
areas where a double rice crop is planted, the fingerlings and early rice must be
harvested between the two rice crops, the field must be worked, and the late rice
must be transplanted. At the same time, the ditches must be redug and fry released.
Therefore, there is a need for more labour than is available. If rice-fish culture is
combined with pond culture these contradictions can be eased. The method is easy
to popularize.
One basic condition is that there be ditches or ponds around the ricefield. The pond
should be 10-30 m2 and about 1.5 m deep. The pond can be dug in advance and
should be linked by a bank to the ricefield. It can also be used to hatch the fry.
After the early rice is transplanted and the fish canal dug, the pond and ricefield
are linked to let the fish in the pond swim across into the ricefield. Just before the
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RICE-FISH CULTURE IN CHINA
early rice is harvested, the fish are driven back into the pond. After the field is
reworked, the second rice crop is transplanted, a ditch is dug, and the fish in the
pond are allowed back into the ricefield.
In 1983 at Lingshan Village in Meichuan District, Guangji County, Hubei
Province, a rice farmer named Hu Maoyu used this method on a 0.17-ha ricefield
linked to a 0.02-ha natural pond. He raised fish in the ricefield for 348 days,
including 117 days when rice and fish lived together (61 days for early rice and
56 days for late rice). He put in 2 143 fry and netted 1770 fish that had a net
weight increase of 216.2 kg and a harvest rate of 82.6% (Table 1). The output was
5 431 kg/ha for early rice and 4073 kg/ha for late rice, or 5.81 % more than the
output from fields in which fish were not raised. Average net income was
CNY2 156/ha. This method is gradually gaining popularity.
Rice-on-Ridges and Fish-in-Furrows
Ridges are built in the ricefield for the rice and fish are raised in the furrows. This
method was developed on the basis of a semidry cultivation method advocated by
Hou Guangjun. This method improves low-yielding ricefields because it makes
multiple uses of available resources. It helps increase the contact of soil and air;
balances water, air, and heat to raise soil temperature; and reduces the formation
of toxic matter. Soil, water, microclimate, and heat are therefore stabilized at an
appropriate level. This stimulates rice to grow roots, which absorb water and
nutrients and changes gravitational water in the ricefield into lateral water that rises
through capillaries to moisten the rice roots. Movement of fish in the furrows
moves the water in the lower strata, stimulates the solution of nutrients, and
increases soil fertility. The deep furrows increase the volume of water stored in the
ricefield and create more room for fish activity. Fertilizers applied in the furrows
make the water fertile and increase natural feed for fish.
In 1986, 16 counties of the Southeast Miao and Tong Autonomous Prefecture of
Guizhou Province popularized this farming method over 688 ha. To ensure its
success, the prefecture and the country earmarked CNY100000 for the project.
Thirty six persons went on a study tour to Sichuan Province and 83 persons from
the Departments of Aquatic Products and of Soil and Agricultural Technique
Popularization were sent to the fields. Various districts, townships, and villages ran
21 training courses for 1000 people. In 1985, a 4.5-ha experiment area yielded
more than 10 350 kg/ha of rice and 472 kg/ha of fish.
Specifically, the method involves digging a ditch, 50-cm wide and 67-cm deep,
and building ridges 70-cm wide (enough to plant 4-6 rows of rice). Mud from the
ditch is spread onto the ridge and rice is transplanted without working the soil. In
a 0.07-ha field, 300 5-cm fingerlings [100 C. idella, 75 silver carp
(Hypophthalmichthys molitirix), 50 bighead carp (Aristichthys nobilis), and
75 C. carpio and C. auratus] are released. During the growing season, green grass
is put into the ditch to feed the C. idella, but no other feed is provided for the other
species.
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PATTERNS AND TECHNOLOGY
Table 1. Results of rice-fish farming in ricefields and adjacent ponds in Lingshan Village,
Guangji County, Hubei Province (1983).
Number
of Fish
Size(g)
Weight
(kg)
Average
Weight
(kg)
Recovery
Rate
(%)
Fry released 10 January
Ctenopharyngodon idella
161
50-150
11
—
—
Cyprinus carpio
300
50-150
32.5
—
—
Hypophthalmichthys molitrix
369
20-50
6.5
—
—
100-350
3
-
-
5.0-6.7 cm
4.8
—
—
Aristichthys nobilis
13
Fry released 16 January
Ctenopharyngodon idella
1300
Total
2143
57.8
Fish harvested 23 December
Cyprinus carpio
271
200-500
70.5
260
90
Hypophthalmichthys molitrix
357
100-400
82.8
235
97
13
300-900
7.8
600
100
Ctenopharyngodon idella
1129
20-650
112.9
—
77
Total
1770
-
274
-
Aristichthys nobilis
83
Research using this high-yielding, high-efficiency semidry cultivation method in
Chongqing City showed that yields of 6750-7450 kg/ha of rice and 705-765 kg/ha
of fish could be achieved. This method has been popularized in the Mianyang and
Huangbo Counties of Hubei Province, and in Hunan and Jiangxi Provinces where
conditions are suitable. Good economic returns have been reported.
Rotating Rice and Fish
In this method, rice and fish are alternatively raised in one ricefield. In 1 year,
only one rice crop is planted, the rest of the time is devoted to fish farming. First,
rice and fish are farmed in one field. When the rice is ripe, the rice and fish are
harvested and the straw is left in the field to rot. Adult fish are then released into
the harvested ricefield. The method can also be applied in double-cropping areas,
but the fish are only raised in winter.
82
RICE-FISH CULTURE IN CHINA
Rotating Rice and Fish in Low-Lying Land
In 1982, this method was adopted on 1.3 ha of low-lying land farmed by the
Luopitang Production Brigade of the Huaqiao People's Commune in Guangji
County, Hubei Province. This piece of low-lying land previously grew only one
late rice crop a year and remained fallow for the rest of the year. On 2 July 1982,
fish ditches (50 cm wide and 27 cm deep) were dug, and the next day, rice
seedlings (Gu-154) were transplanted at a distance of 11.5 x 17 cm. The field was
not weeded during the entire rice-growing season and no pesticides were applied.
Only 300 kg of sodium bicarbonate (232.5 g/ha) and 140 kg of urea as a top
dressing (109 kg/ha) were used. The rice output was 5 530 kg, 10% more than the
expected 5000 kg, with a per-unit output of 4298 kg/ha. On 23 July,
19690 fingerlings [84% C. idella, 5% black carp (Mylopharyngodonpiceus), 10%
H. molitirix, and 1 % A. nobilis] were introduced at a rate of 115 300/ha. The fish
were grown for 64 days without feed and on 24-25 September, 10094 fish,
weighing a total of 229.5 kg (176.5 kg/ha) were collected. Ten percent of the fish
were 10 cm in length, 70% were 10.1-20 cm, and 20% were over 20.1 cm.
During the second rotation season, 10787 fingerlings (vaccinated for C. idella
bleeding) were introduced (8385/ha). The total weight was 279 kg and the average
size of the fingerlings was 15.6 cm. A small amount of fertilizer was applied after
January 1983 and the rate was increased after April. During the entire rotation
season, 40 kg of urea, 1450 kg of night soil, 600 kg of vegetable cake, 3 508 kg
of azolla, and 1830 kg of green grass were applied. Because 5 500 kg of rice straw
were left in the field, the total amount of fertilizer and feed was 12 928 kg.
On 26-27 June 1983, 1 689 kg of fish (average 1 300 kg/ha) were harvested.
Excluding the fingerlings, the net catch was 1095 kg/ha. The net income from fish
alone was CNY2519, or an additional CNY1957/ha.
Raising Fish hi Winter Ricefields
This rotation method makes full use of the ricefields after the late rice harvest until
the middle rice is planted the following summer or the next late rice crop is
planted. In some areas, fingerlings are released right after late rice is transplanted,
and the fish are harvested either before the spring festival in January or February
or before the next early rice crop is transplanted. This method yields a high output
offish, mostly as food. During the winter season, most ricefields store water that
is overgrown with plankton and bottom organisms, especially in East Sichuan
Province. This water is very suitable for fish.
In the winter of 1983, Cheng Jinghong of the Freshwater Products Institute of
Fujian Province reared fish in three pieces of land covering 0.25 ha at the Andou
Fry Farm, Jinjiang County, Fujian Province. On 20 November 1983, he released
57.5 kg of fingerlings (C. idella, C. carpio, H. molitrix, and A. nobilis). On
28 March 1984, 128 days later, he collected 85 kg of fish, a net increase of
27.5 kg. The weight of C. carpio increased 5-8 fold (average 0.2 g/day), and the
PATTERNS AND TECHNOLOGY
83
survival rate was 89.3%. After the costs for fingerlings and feed were deducted,
the net profit was CNY92 (CNY5 520/ha).
Cheng Jinghong raised the field bank by 50 cm and packed it firm after harvesting
the late rice. He dug a ditch 30-cm wide and 30-cm deep along the field banks
(1m from the banks) and dug two fish ditches or pits (each covering 1 m2) near the
water inlet. He installed screens at the inlet and outlet of the field, stored water in
the field, and released the fingerlings. Fish feed consisted of peanut cake, rice
husk, wheat bran, and fish powder mixed in a ratio of 8:6:5:1 with water. The
mixture was spread in the ditches or put on a food platform at 14:00-15:00 each
day. The total amount of feed used was 2-3% of the total weight of the fingerlings,
depending on the weather and how well the fish fed.
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New Techniques for Raising Fish in Flooded Ricefields
Wan Banghuai23 and Zhang Qianlong24
The traditional model of raising fish in ricefields has been practiced for a long
time. It does not include digging ditches or pits; therefore, the field remains flat.
With this model, fish raising and rice growing do not interfere with each other.
This method proved that fish and rice could coexist and elucidated the relationship
between fish and rice. It inspired the theory of rice-fish mutualism in ricefields.
This traditional model suited cultivation systems in which high-stalk strains of rice
were planted in ricefields with relatively high water levels. The fields were not
directly exposed to the sun, weeding was not performed, and chemical fertilizers
and pesticides were not applied. The model helped improve skills in fish raising in
ricefields and promoted reforms in the cultivation system. The fact that fish raising
in flat ricefields has been in practice for over 2 000 years clearly demonstrates the
viability of this technology.
However, the traditional model had disadvantages. The technology was not fully
developed, management was poor, production was on a small-scale and done
spontaneously by farmers, and the method was limited to hilly, mountainous areas
and areas with sufficient water. The fish that were raised were usually a single
species, small in size and in quantity. Yield was low (75-150 kg/ha) because of
extensive raising and poor management. Moreover, production was subject to the
constraints of the cultivation system and natural disasters. Therefore, development
was slow and unstable. The history of fish-raising in flat ricefields in Jiangxi
Province illustrates this slow development. The amount of land devoted to rice-fish
culture was 3 300 ha in 1956, 2 800 ha in 1957, 3 470 ha in 1958, 14 620 ha in
1959, 20640 ha in 1960, 10570 ha in 1961, and 12520 ha in 1962. There was a
steady decline until 1976, when fish raising in ricefields became virtually extinct.
The area gradually increased again and by 1983 reached 18 700 ha.
Emergence of the New Technology
Fish culture in flat ricefields developed to its height in the 1950s and 1960s in
China when it covered a total area of 0.7 million ha. By 1986, the area had grown
to 1 million ha; however, the following year it declined to 0.73 million ha. Fish
yield was less than 150 kg/ha. The cultivation system has changed, but fish raising
23
Aquatic Products Department, Jiangxi Provincial Bureau of Agriculture
Animal-Husbandry and Fishery, Nanchang, Jiangxi Province.
24
Agriculture, Animal-Husbandry, and Fishery Department, Yichun
Prefecture, Yichun, Jiangxi Province.
86
RICE-FISH CULTURE IN CHINA
in ricefields has not completely returned to its peak level, and even in areas where
rice-fish production has been restored or developed it is still normally based on flat
ricefields.
However, in some areas, fish raising in ricefields has been more highly developed.
For example, in 1984-1986 demonstration areas (66000 ha of ricefields) were
cooperatively developed in 18 provinces, municipalities and autonomous regions
all over the country. Fish yields reached 300-750 kg/ha (maximum 1500 kg/ha),
and rice output increased by about 10%.
New models were developed in the 1960s. These reforms in the cultivation system
led to increased rice output, but also sharpened the conflicts in fish raising in
ricefields. Because the old model was no longer suitable, efforts were made to find
solutions to these conflicts. During 1959-1960, people in Jihe Village, Yaoxia
Township, Suichuan County, Jiangxi Province, raised fish in double-cropping
ricefields by digging ditches and pits (more or less like the current ditch-pit
models). Fish yields reached 375 kg/ha. However, this technique remained on a
small scale of only 0.67 ha and yields remained constant for over 20 years. It was
not until the beginning of the 1980s that progress was made.
In 1982, scientists in Jiangxi Province began to systematically spread the new
technology over the entire province and to promote the theory of the supportive
coexistence of rice and fish. Extensive research was conducted on several rice-fish
cultivation models: flat ricefield, ditch-pit, wide-ditch, zigzag ditch, small pit, field
pond, semidry ridge and ditch, and ridge-ditch.
In 1984 and 1986, cooperative extension efforts were undertaken in 18 provinces,
municipalities, and autonomous regions. In Jiangxi Province, the Provincial
Aquatic Products Department sponsored and entrusted the cities and prefectures of
Yichun, Wanzhai, Shangyou, Suichuan, Puyang, Fengxin, Shanggao, and Anyi to
conduct technical extension and demonstrations of ditch-pit, ditch-pond, and ridgeditch models. In Jiangxi Province, this marked the beginning of the expansion of
the new technology.
Advantages and Disadvantages
The new technology is based on the theory that raising fish in ricefields and
growing rice with fish improves the harvest of both crops. Rice-fish culture
improves the ecological cycling of material and energy in the ricefields and
therefore enhances the growth of rice and fish.
Fish raising in ricefields can be classified into various categories based on
cultivation system: simultaneous cropping of rice and fish, rotation cropping of rice
and fish, and intercropping of rice and fish. It can also be classified according to
crop system and raising method into fish raising in double-cropped ricefields,
fallow winter fields, lotus fields, and wild-rice fields. From the point of view of
engineering, technology, and technique, rice-fish culture can be divided into flat-
PATTERNS AND TECHNOLOGY
87
field, ditch-pit, and ditch-pond (inclusive of small pond, wide and semidry ridge,
and ditch-in-the-middle sided by rice). All these models are now in use.
Ditch-pit model. In Jiangxi Province, this is the primary model for the new
technology. Fish are raised in ricefields in open ditches and pits. Each ditch is as
wide as two rows of rice and is 24 cm deep (or as deep as the hard layer of soil).
The pits are 50-70 cm deep and 1 m2 in area. One or two pits are placed at each
inlet and outlet for water at the corner(s) of the field. Rice seedlings are planted
along the sides of each ditch and along three sides of each pit to serve as a fence.
This model does not require much work or a large investment, it is easy to operate,
and can be used in most fields. The conflicts between rice and fish are mitigated,
rice output can be increased by 10%, and fish yields can be doubled or tripled
compared with flat ricefields. Farmers readily adopt this model; however, because
the ditches are shallow and the pits small, the fish are grown for a limited time and
are small. These fish can be used as fish fry or as food by the farmers, but cannot
be sold in the market. The yield is low.
Ditch-ridge model. A semidry rice planted on raised ridges is combined
with fish culture in the ditches. At the same time, lotus, wild rice, and azolla are
grown in the ditches. One advantage of this model is that there are many ditches
filled with water where azolla can be grown as fish feed. This solves the conflict
between rice and fish. The fish can be raised for a longer time and be given
supplemental feed. Fish yields easily reach 750 kg/ha. This method improves the
yield from ricefields and creates economic benefits.
The disadvantage of this model is its limited adaptability, particularly in Jiangxi
Province, which is dominated by double-cropped rice. As well, the method
requires a lot more work that must be repeated each year. Therefore, this model
is not well accepted by farmers, and extension efforts have only been successful in
establishing this model in 0.5% of the areas involved in rice-fish farming in the
province.
Ditch and pond model. This is the most widely used model in the province
because it can be practiced in different ways to suit local field conditions. A small
pond is dug at one end of the field, or shallow pond(s) between the ricefields can
be used. The ponds are 1-m deep and occupy only 6-8% of the total field area.
The ditches are 30-50 cm deep and cover about one-third of the total pond area.
This model provides an optimized environment by using improved engineering and
by extending and controlling the time available to raise the fish. Different varieties
of commercial-size fish can be grown yields are 750-1500 kg/ha. Rice production
is also increased by over 5 %. This is an ideal model for raising fish in doublecropped ricefields. The disadvantages of this model are that a lot of labour is
involved, the engineering work must be done each year, and the fish cannot be
grown during the winter.
88
RICE-FISH CULTURE IN CHINA
Principles and Economic Benefits
The new technology can create an artificial ecosystem that is similar to the natural
ecosystem. The new models attempt to develop cash crops and livestock that are
suitable for socioeconomic development. These models incorporate the advantages
of pond raising. They produce high yields and fully use the ecological conditions
of the ricefield. The fish have sufficient natural feed and this can be supplemented
with artificial food. Therefore, conflicts between rice and fish are resolved and a
balanced ecosystem is developed in which it is possible to increase the output of
both rice and fish.
Empty spaces and small patches of land can be used by putting up shelters that not
only provide refuge, but also provide suitable conditions for crops such as melons.
Vegetables and beans can be planted on the ridges, and lotus, wild rice, taro, and
azolla can be raised in the water. This comprehensive use of the land makes it
possible to obtain good harvests of rice, fish, and vegetables. Because the model
makes good use of land, water, biological, and nonbiological resources in the
riceflelds, it is an ideal model of production for fish-rice culture. Substantial
ecological, economic, and social benefits are produced.
Biological Benefits
Weeding and fertilizer. Grasses that grow with rice absorb available
fertilizer and compete for nitrogen. When 500-600 fish that feed on grass are
raised, the grass is kept under control and the fertilizer is reserved for the exclusive
use of the rice. Experiments have shown that every 1000 g of grass-eating fish fry
can eat as much as 40-60 g of weeds/day. Experiments in 1988 in the Shang-gao
area showed that a 500-g grass carp (Ctenopharyngodon idella) can eat 3.5 g/day
of weeds in a ricefield and therefore turn weeds into fish protein. Fish excrement,
in turn, fertilizes the rice, increases organic matter in the soil, and improves the
fertility of the ricefield.
Pests and plant diseases. The insects (and their eggs) that harm rice are
good food for the fish. When insects move about in the water, or when their eggs
fall into the water, they are eaten by the fish. In this way, fish raising benefits the
rice because it reduces plant diseases and eliminates pests. In experiments in the
Shang-Gao area, a 150-g common carp (Cyprinus carpio) was found to eat 1.3 g
of insect pests each day. One study compared the index of harm caused by pests
(e.g., leaf folders and stem borers) and found that the leaf folding rate of every
100 clusters of rice was 90 cases in ricefields with fish and 210 in ricefields
without fish. The rate of blight was zero in ricefields with fish and 0.014% in
ricefields without fish. Fish also help rid rice plants of surplus tillers and diseaseridden leaves. This increases the penetration of light and reduces the occurrence of
plant diseases and pests.
In addition, the movements of fish stir the water and soil, which increases oxygen
in the water, speeds the release of fertilizer in the soil, and improves the
development of the root system of the rice. Loosening the soil, eliminating weeds,
PATTERNS AND TECHNOLOGY
89
Table 1. Results of demonstration work using the new technology to raise fish in ricefields
(organized by the Jiangxi Provincial Aquatic Products Department, Jiangxi Province).
Increase
in Rice
(kg/ha)
Average Added
Value of Rice
and Fish
(CNY)
Ratio of
Investment
to Added
Value
Year
Area
(ha)
Fish
Catch
(kg/ha)
1984
247
605.7
1651.8
214
271
1:11.8
1985
278
593.1
823.5
215
593
1:5.5
1986
445
690
408
17£
546
1:4.8
Investment
(CNY/ha)
* Includes income from 4 kg of lotus seed (an increase of 8.7%).
and adding fertilizer raises rice production in many ways. The need to weed by
hand is eliminated and reduced amounts of chemical fertilizer and insecticide are
needed. These benefits produce savings in labour and investments and help
improve the rural environment and the health of the people.
Economic Benefits
Rice-fish culture using the new technology makes multiple uses of available land.
It is an intensive farming model that requires a small investment, is highly
efficient, and produces quick benefits. The results of the new technology are
illustrated by demonstration work organized by the Jiangxi Provincial Aquatic
Products Department from 1984 to 1986. The lowest ratio of investment to added
value was 1:4.8; the highest was 1:11.8 (Table 1). An investment of CNY36
produced an increased value of CNY 175. At the high end, an investment of
CNY 18 produced an increased value of CNY214. These figures do not include the
extra income generated from melons, vegetables, and beans.
Social Benefits
Increased employment. Surplus labour is employed. This is particularly
true in poor mountainous areas where only a limited amount of arable land is
available and there are few opportunities for sideline occupations. In Suixiang
Township, Yichun Prefecture, for example, although many people were engaged
in sideline occupations in the past, many others often visited relatives or friends
because they had a lot of leisure time. Now, in over 95% of the nearly 46.7 ha of
ricefields, fish are raised. The people are happy: fish raising in the ricefields gives
people things to do and that they live contentedly.
More fish to market. Fish are a well-liked source of high-quality animal
protein. The average per capita consumption of fish in China is 10 kg/year; in
Jiangxi, it is only 6-7 kg/year. It is difficult to supply fish to hilly and
90
RICE-FISH CULTURE IN CHINA
mountainous areas. However, the extensive development of rice-fish cultivation
and efforts to increase fish catch will help activate the urban and rural markets and
supply more fish for the table.
Increase of income. Fish raising and the associated intensive farming are
attractive to farmers because of the increased yields of rice and fish and the income
derived from other cash crops. The extension of the new technology will promote
reforms in the cultivation system, further enrich rice-fish farming, and further
develop agriculture and increase national income.
Conclusion
Research and extension using the new technology are similar in Jiangxi Province
to other places in China. These models can be further improved if they are adapted
to local conditions and if rice output is increased. The new technology will be
extended through the process of application, and perfected through extension.
For thousands of years, fish raising in ricefields in China has been more advanced
than in other countries. However, considering China's favourable natural
conditions, the wisdom of the people, and the fact that China is basically an
agricultural nation, development has been slow and unbalanced, and the amount
of land devoted to rice-fish farming is limited. Moreover, the catch is still low
(about 150 kg/ha on a national scale over a million ha). The new technology and
its different models are still in the primary stages of development.
Administrative and professional leadership is needed. An agricultural extension
program must be established to encourage fish raising in ricefields. This is the only
way that the technology can be introduced to transform flat-type agriculture into
three-dimensional agriculture and to produce increased yields and generate more
income.
Methods of Rice-Fish Culture and their Ecological
Efficiency
Wu Langhu25
Rice-fish culture is the best model of an artificial ecological system. Rice is
predominant, but weeds, plankton, and saprophytic and photosynthetic bacteria
compete with the rice plants for nutrients and diminish the environment. The
introduction of fish into the ricefield creates a new link in the food chain that uses
energy that would otherwise be lost and improves the function of the system and
its economic efficiency. Appropriate techniques make bumper harvests of rice and
fish possible.
Models of Rice-Fish Culture
Intercropping of Rice and Fish
This model is suitable for most types of ricefields. It requires ample water
resources. Before the fish are introduced, ridges (50-70 cm high) and fish ditches
are constructed. The number of ditches is determined by the size of the field. Each
ditch is 33-50 cm wide and 25-30 cm deep. A pit (100 cm long, 50-70 cm wide,
and 80-100 cm deep) is dug where the ditches cross. The distance between the
ridges and the ditches is 40-60 cm. Rice plants on the ditches and the pit are
transplanted near the ridge to form a fence or marginal row. All water inlets and
outlets are fitted with screens to prevent the fish from escaping. About
19 500-225 000 summer fingerlings of summer grass carp (Ctenopharyngodon
idelld) are introduced per hectare.
Rotation of Rice and Fish
This model is suitable for cold-water fields. Its pattern is one season rice, one
season fish. Ridges (100 cm high and 50 cm wide) are built and then
1000-1500 summer fingerlings of C. idella are introduced per hectare. When the
rice matures, the grain is harvested but the straw is left in the water. Another
5 000-7000 fingerlings of silver carp (Hypophthalmichthys molitrix) and variegated
carp (C. carpio) are then introduced per hectare.
Rice-Fish with Ridge
This model is suitable for marshy lowlands or deep, cold, water-logged land. Rice
is planted on ridges and fish are reared in ditches. The ricefield is reconstructed in
25
Hubei Aquatic Science Research Institute, Wuhan, Hubei Province.
92
RICE-FISH CULTURE IN CHINA
two steps. First, ditches (50 cm deep and 20 cm wide) are constructed to cover
45-50% of the field, and ridges (20-130 cm wide) are built with soil from the
ditches. Second, the ridges are levelled with mud from the ditches. Rice seedlings
are transplanted close together on the ridge surface. Close planting compensates for
the space taken up by the ditches. About 1500-3000 winter fish fmgerlings and
12000-18000 variegated carp fmgerlings are introduced per hectare.
Rice-Fish with Fish Pit
The fish-pit model is devised according to the principles of fish-pond culture. The
technique provides 7500kg of rice and 750 kg offish26 and solves the problems of
drying and of applying fertilizer and insecticide. A pit is dug on one side of the
field and covers about 8-10% of the area of the field. The pit should be 2-3 m
wide and 1.5-2 m deep. Its length depends on the length of the field. The pit can
be used to hatch carp fmgerlings, breed summer or winter fmgerlings, and raise
adult fish. About 3 000-5 000 summer or 300-500 winter fingerlings are introduced
per hectare.
Rice-Fish with Wide Ditches
In addition to the ridges and the ditches used in the mutualism model, this model
requires that a wide ditch (1-2 m deep and 1-2 m wide) be dug along the side of
the water entrance of the field. The wide ditch usually takes 7-10% of the area of
the ricefield and has an inner ridge (26 cm high and 23 cm wide). Between the
wide ditches, at intervals of 3-5 m, are passageways. About 4500-7500 winter
fingerlings are introduced per hectare. The wide ditches can also be used to hatch
fingerlings.
Economic and Ecological Efficiency of Rice-Fish Culture
Economic Indicators
An experiment was conducted between 12 May and 15 July 1983 in three
neighbouring ricefields (0.15 ha, 0.07 ha, and 0.01 ha). The ricefields produced
good harvests of early maturing rice under both drought and water-logged
conditions. The 0.01-ha field was used as the control. By the end of the
experimental period, fingerlings in the control ricefield reached an average length
of 8 cm, and 936 C. idella were harvested. The rate of recovery was 50%. Rice
yields in the two experimental fields were 7584 and 7992 kg, an increase of
1209 kg/ha (19%) and 1 617 kg/ha (25%) over the control (Table 1).
In October 1984, similar results were obtained in another experiment with late
maturing rice. Four plots (each 141 m2) were established in a 0.08-ha field. Three
26
The popularization slogan for increasing rice-fish production was
thousand jin rice grains, hundred jin fish based on the Chinese units per mu
(1 mu=0.07 ha; 1 jin =0.5 kg).
93
PATTERNS AND TECHNOLOGY
Table 1. Yields of early maturing rice in a rice-fish field and a control field.
Yield Panicle No.
(kg/ha) (10000/ha)
Panicle
Length
(cm)
Total No.
of Grains
per Panicle
Fertility
Rate
(%)
1000-Grain
Weight
(g)
Treatment 1
7585
367.5
18.7
94
91.1
24.8
Treatment 2
7962
367.5
18.6
107
92.2
24.8
Control
6375
366
17
87
87
24.8
Table 2. Yields of late-maturing rice in a rice-fish field and a control field.
Yield
(kg/ha)
Panicle No.
(10000/ha)
Total No. of
Grains per
Panicle
Fertility
Rate
(%)
1000-Grain
Weight
(g)
Treatment 1
7439
312
104
80.3
28.5
Treatment 2
7700
285
116.8
81
28.7
Control
6573
259.5
111.6
78.6
28.6
plots were used as replicates, one as the control. The rate of increase in rice yields
was 10.2-20% (Table 2). Tables 1 and 2 show that rice-fish culture can increase
effective tillering, improve the grain fertility rate of the rice, and increase (or at
least maintain) the fertility of the field.
Effect on Weeds
On 29 July 1982, the amount of weeds in two fields were measured. In the field
with 100.8 kg of weeds, fish were introduced. In the field with 44.2 kg of weeds,
no fish were introduced. On 13 October, there were 20.2 kg of weeds with the fish
and 273.0 kg without the fish. Similar results were obtained in 1984-1985. In
experimental plots in October 1984, there were 2.0 kg (148.5 kg/ha) of weeds in
the field with fish, and 29.8 kg (2 100 kg/ha) in the field without fish. The field
with fish had 1951.5 kg/ha less weeds. On 2 May 1985, before fmgerlings were
introduced, the amount of weeds averaged 1504 kg/ha. On 27 July, after fish had
been raised for 2 months, there were 17.1 kg of weeds in the treatment fields and
263.1 kg in the control fields. About 246 kg of weeds had been eaten by the fish.
Increase in Soil Porosity
Porosity directly influences the ability of the soil to retain water, the aeration of the
soil, and the movement of water. It also indirectly affects the activity of aerobic
and anaerobic bacteria and therefore influences the decomposition rate of organic
substances and the capacity of the soil to provide nutrients. The activity of the fish
94
RICE-FISH CULTURE IN CHINA
Table 3. Influence of rice-fish culture on the physical properties
of soil in late maturing ricefields.
Porosity
3
Sampling Date
Unit Weight
Treatment
(g/m )
(%)
27 August
Fish raising
-1
1.37
48.3
-2
1.36
48.7
-3
1.39
47.6
1.38
48
-1
1.24
59
-2
1.25
52.8
-3
1.25
52.8
L47
44.7
Control
27 October
Fish raising
Control
can lessen the unit weight of the soil, increase its porosity, and therefore improve
ventilation.
This increase in soil porosity has been experimentally verified. Experiments in
October 1982 showed that soil porosity of a field with fish was 59%; whereas,
porosity in a field without fish was 53%. In other experiments in 1984, soil
samples were taken twice. The first samples showed no difference in soil porosity.
The second samples, taken after 2 months of rice-fish culture, showed that soil
porosity in the field with fish was 8.1-14.3% higher than that in the field without
fish (Table 3).
Fertilization of Fields
Rice plants obtain two thirds of their nutrients from the soil and one third from
fertilizer applied during growth. However, weeds, plankton, and saprophytic and
photosynthetic bacteria compete with rice for nutrients. Weeds can reduce rice
yields by 10-30%.
Rice-fish culture can eliminate or inhibit weeds and help retain soil fertility. Only
about 30% of the weeds and plankton eaten by fish are digested and absorbed,
about 70% are excreted, which increases the organic matter content and fertility
of the soil. This was verified by testing the organic and alkaline-nitrogen content
of the soil in ricefields with and without fish (Table 4). The ricefield with fish
showed increases of 0.114% in organic nitrogen, 6.95 ppm in alkaline nitrogen,
and 0.0044% in total nitrogen, compared with ricefields without fish.
95
PATTERNS AND TECHNOLOGY
Table 4. Influence of rice-fish culture on the organic and nitrogen content of soil in
ricefields.
Sampling Date
Treatment
Organic
Matter
(%)
19 October 1982
Fish raising
2.19
100.6
0.1288
Control
2.09
93.6
0.1244
Fish raising
3.05
137.0
0.0763
Control
3.26
142.0
0.0733
Fish raising
3.25
151.1
0.0712
Control
3.13
140.0
0.0588
Fish raising
4.44
134.8
0.0811
Control
3.36
128.5
0.0623
Fish raising
4.67
147.0
-
Control
4.60
140.0
—
Fish raising
3.52
134.1
0.089
Control
3.29
128.8
0.08
8 August 1984
27 August 1984
12 October 1984
25 July 1985
Mean
Alkaline
Nitrogen
(%)
Total
Nitrogen
(g/m3)
Table 5. Numbers of planthoppers in ricefields with and without fish (1984).
Clumps
Imago
Larva
Insects
per 100
Clumps
I
10
5
58
630
20
4
31
175
II
10
4
40
440
20
3
27
150
III
10
2
68
700
20
14
37
255
Mean
10
3.7
55.3
590
20
7
31.7
193
I
10
6
69
750
20
7
52
295
II
10
2
57
590
20
7
28
175
HI
10
6
106
1 120
20
9
42
225
Mean
10
4.7
77.3
820
20
7.7
40.7
232
Generation
Clumps Imago Larva
Insects
per 100
Clumps
Fish Raising
Control
96
RICE-FISH CULTURE IN CHINA
Insect Control
Fish eat harmfiil insects and their larva, especially planthoppers. In an experiment
in September 1982, three fish from a ricefield were dissected. Leafhoppers and
planthoppers were found in the bellies of common carp and silver carp. In 1984,
the population density of snout-moth larva and leafhopper were investigated. Fish
were dissected to determine their capacity to eat insects. In the ricefield without
fish, there were 820 snout moths and 11275 leafhoppers; in the ricefield with fish,
there were only 692 snout moths and 10127 leafhoppers. When the fish were
dissected 3 of the 10 C. idella had snout moths in their digestive organs, and all
10 contained 2-3 leafhoppers. More leafhoppers were found in C. idella that were
more than 7 cm long.
Li 1985, a detailed investigation was done on planthoppers (Table 5). The number
of planthoppers per 100 clumps of rice in ricefields with fish was 17-28% less than
that in fields without fish. By the fourth generation of planthoppers, there were
820 per 100 clumps of rice in the ricefield without fish, which was enough to
warrant the use of an insecticide. The ricefield with fish had only 590 planthoppers
per 100 clumps of rice and no insecticide was needed. Rice-fish culture can also
help control mosquitoes, which significantly improves the health of people in rural
areas.
Ridge-Cultured Rice Integrated with Fish Farming in
Trenches, Anhui Province
Yon Dejuan27 Jiang Ping,27 Zhu Wenliang,28 Zhang Chuanlu,29 and
Wang Yingduo29
The earliest record of rice-fish farming in Anhui is from the Ming Dynasty.
Traditional techniques produce low yields; however, improved methods have been
introduced in recent years in many parts of the country. Changes include mixed
culture of fish instead of monoculture; release of adult fish instead of fry; provision
of feed for the fish; and disease prevention and control. Research on biology and
ecology have attempted to find ways to increase the yields of rice and fish.
Engineering facilities for rice-fish farming have been continuously modified. Some
new ecological techniques include digging trenches that surround the field,
horizontal trenches, and ditches, semidry cultivation, and ridge-cultured rice
integrated with fish farming in trenches (high ridge and deep trench).
Advanced Cultivation Techniques
In 1987, the Provincial Aquatic Product Technique Extension Station in Fengtai
County, Anhui Province, conducted experiments and established a project to
demonstrate advanced techniques of ridge-cultured rice integrated with fish farming
in trenches that obtained bumper harvests of rice and fish.
Selection of Experimental Plot
A 7.1-ha ricefield managed by 31 households at Xinji Village, Chengbei
Township, Fengtai County, was selected. The plot was smooth and had medium
soil fertility and a convenient irrigation and drainage system. The cropping pattern
was wheat-rice. Field preparation began in early June after the wheat harvest.
Trenches were dug and ridges constructed. Ditches (1-1.7 m deep and 1.5-2 m
wide) were dug in 3-7% of the ricefield. Three types of ditches were used:
•
Ridge type. Ridges 50 cm wide with two rows of rice seedlings
spaced 25 x 12 cm; 165000-168000 plants/ha with each hole
27
Anhui Aquatic Product Technique Extension Station, Hefei, Anhui
Province.
28
Fengtai Animal Husbandry and Anhui Bureau of Aquatic Product,
Fengtai, Anhui Province.
29
Chengbei Township, Fengtai County, Anhui Province.
98
RICE-FISH CULTURE IN CHINA
•
•
containing 1-2 transplanted rice plants; trenches 50 cm wide and
40 cm deep.
Wide ridge type. Ridges 1 m wide with six rows of transplanted rice
seedlings, rows and plants spaced 20 x 20 cm; 180000186000 plants/ha; trenches 50 cm wide and 40 cm deep.
Bed type. Bed 2 m wide with 12 rows in the bed, rows and plants
spaced 20 x 22 cm; 195 000-201000 plants/ha; trenches 60 cm
wide and 40 cm deep.
Plot Management
Before the rice seedlings were transplanted, 600-900 kg/ha ammonium sulphate
and 450-600 kg/ha calcium superphosphate and manure were applied. From 15 to
20 June, seedlings of hybrid rice varieties (Xianyou 3 and Xianyou 6) were
transplanted. A week later, fish fingerlings were released. For adult fish culture,
2700-3000 fingerlings (10-20 cm in length) were released. The major varieties
for fish culture were grass carp (Ctenopharyngodon idella) and common carp
(Cyprinus carpio) mixed with a few variegated carp (C. carpio), silver carp
(Hypophthalmichthys molitrix), and crucian carp (Carassius carassius). For
fingerling production, about 225 000-300 000/ha C idella and C. carpio
fingerlings 3-5 cm long were released into the ricefield.
To accommodate the water requirements of both the rice and fish, the depth of the
irrigated water was controlled according to the needs of the different growing
stages of the rice. A week after the rice seedlings were transplanted, the ridge was
flooded to a depth of 3-6 cm. After the seedlings turned green, the field was
irrigated frequently. The trench was kept full of water to saturate the ridge and
promote the growth of the plant-root system. The time from booting to milking is
the peak period when both rice and fish need water; therefore, the ridge was
flooded to a depth of 7-10 cm with irrigation water. After the rice had reached the
milking stage, the trench was filled with water to continuously saturate the field
and ensure full development of the rice grains. During the growth period for the
rice plants, 7-10 kg of urea applied as one or two top dressings were used
according to the soil fertility of each plot. Two or three applications (one or two
times less than that applied in ricefields without fish) of pesticide were used
depending on the rate of insect-pest infestation.
In early September 1987, the fields surrounding the experimental plot at Chengbei
Township were attacked by rice planthoppers. The farmers shook the rice plants
with sticks to knock the planthoppers into the water. This method of controlling
insect pests did not use chemicals that pollute the environment and provided fish
with additional food.
Fish management included control and prevention of disease, prevention of fish
escape, the timed supply of feed in the ricefield, and the culture of adult C. idella
mixed with secondary fish varieties. The feed consisted of fodder grass
(10500-12000 kg/ha) and concentrated feed (450 kg/ha). In ricefields in which
99
PATTERNS AND TECHNOLOGY
Table 1. Rice yields from different culture types.
1000Grain
Weight
(g)
Empty
Grains
(%)
Type
Area
(ha)
Harvest
(kg/ha)
Hills/
ha
Ridge
0.5
7125
165000
13.9
107.9
30.2
18.6
Wide ridge
0.8
6870
195000
12.3
115.6
28.6
19.7
Bed
2.9
6990
195000
10.9
112.2
30.0
23.2
Conventional
4.3
6795
232500
9.1
114.0
29.1
25.6
Control
0.3
6150
249000
8.8
105.0
29.0
21.6
Panicles/ Grains/
Hill
Panicle
grass carp were the main fish variety, concentrated feed and green feed were used;
in ricefields with fingerlings 450 kg/ha of concentrated feed and some green feed
were applied.
Rice and Fish Yields
Rice yields. On 10 September, before the rice was harvested, a sample was
taken of ridge-cultured rice integrated with fish farming. There were
15.5 panicles/bunch, 175 kernels/panicle, and 19.2% empty grains. With the other
types of rice-fish farming, there were 12 panicles/hill, 166.8 kernels/panicle, and
19.3% empty grains. An estimate of yield was made by selecting a representative
plot from each experimental model. The yield of each experimental plot was
independently calculated after the harvest (Table 1). The rice yield from the ridgecultured rice integrated with fish farming was 1-5% higher than from conventional
rice-fish farming (Table 1). The ridge-cultured rice-fish system produced 12-16%
more rice than ricefields without fish.
Edge effect. Experiments on wide-ridge rice-fish farming in Huo Shan
County in 1987 indicated that the number of panicles per bunch, grains per panicle,
and weight per thousand grains were higher in outside crop rows than in the rows
at in the centre (Table 2). However, the ridge and wide-ridge systems require
excessive labour to dig the trenches. Field preparation and transplanting is done
during the busy season; therefore, it is difficult to popularize this method.
Fish yield. Before the rice harvest, adult fish with commercial value were
marketed;, the remaining fish were counted, weighed, and put into the trenches and
fishpond. The fingerlings were 10-20 cm in length, the adult C. idella weighed
0.5-1.5 kg, and H. molitrix weighed about 0.5 kg. The total harvest of fish from
the wide-ridge treatment was over 800 kg of adult fish and 312 kg of fingerlings
per hectare (Table 3).
100
RICE-FISH CULTURE IN CHINA
Table 2. Growth indicators and harvest of rice cultured on wide ridges in
Huoshan County (1987).
Panicles/Hill
1 000-Grain Weight
(%)
Grains/Panicle
Project/Head
of Household
OR'
CR
RI
(%)
OR
CR
RI
(%)
OR
CR
RI
(%)
YeLiping
16.0
12.4
29.0
230.0
135.0
70.0
24.4
24.0
1.7
YeYoumiao
14.5
9.3
56.0
127.0
88.0
44.0
27.3
24.5
11.5
TangQiancun
25.0
21.0
19.0
164.0
107.0
53.0
28.0
25.0
12.0
" OR outside row; CR central row; and RI rate of increase.
Table 3. Comparison offish yield between different culture types.
Fingerlings
Adult Fish
Type
Yield
(kg/ha)
Survival
Rate (%)
Yield
(kg/ha)
Survival
Rate (%)
Growth
Factor
Ridge
396
46.5
97.5
79.3
7.3
Wide ridge
312
44.7
804
74.5
6.8
Bed
204
47.1
-
-
-
Conventional
167
38.4
—
—
—
Economic Efficiency Analysis
Production value and cost accounting showed that Income from the ridge and wideridge fish farming systems was much higher than from conventional rice-fish
culture. Income from the ricefields with adult fish culture was also higher than the
income from the field with fingerlings. Net income was 2-3 times greater than that
from ricefields without fish culture (Table 4).
Discussion and Conclusion
Ridge-cultured rice integrated with fish farming in trenches has several advantages.
It is suited to lowland ricefields, cold waterlogged fields, and level ricefields. The
optimum sizes for the ridges and trenches are being studied in different parts of the
country. The economic efficiency of the ridge-based system is higher than for
conventional rice-fish farming. The rice plants grow vigorously and have many
PATTERNS AND TECHNOLOGY
101
Table 4. Comparison of economic efficiency of different culture models.
Income (CNY/ha)
Expenditure (CNY/ha)
Rice
Fish
Total
Total
Net
Income Income
3690.0 5653.5
469.5
760.5
1230.0
2080.5
3216.0
5296.5
487.5
751.5
1239.0 4057.5
8
2287.5
1980.0
4267.5
507.0
313.5
820.5
3447.0
12
2325.0
1561.5 3886.5
499.5
289.5
789.0
3097.5
Bed
43.5
2376.0
1018.5 3394.5
495.0
237.0
732.0
2662.5
Conventional
6.5
2310.0
831.0
3141.0
501.0
171.0
672.0
2469.0
Control
4.5 2089.5
-
2089.5
589.5
-
589.5
1500.0
Area
(ha)
Rice
Ridge
8
1963.5
Wide ridge
24
Ridge
Wide ridge
Treatment
Fish
Total
Income
Adult Fish
4423.5
Fingerlings
large panicles and full grains. The wide-ridge system requires less labour than the
ridge system and is therefore easier to popularize.
The wide-ridge system and especially the ridge system are more economical and
efficient than conventional rice-fish culture because:
•
•
•
Frequent irrigation with shallow water is the most appropriate
environment for rice growth and development. The model of ridgecultured rice integrated with fish farming in trenches is suited to
irrigation with shallow water.
Hybrid rice, the high-yielding varieties, need wider spaces between
rows and narrow spaces between plants. Ridge-cultured rice
integrated with fish farming in trenches fulfils these requirements
and provides suitable growing conditions for high-yielding varieties.
The ridge and wide-ridge systems can alleviate the conflicts between
the water requirements of rice and fish. These systems meet the
need of rice for water depth at different growing stages, provide a
good environment for fish, and enlarge the holding capacity for
fish. They also make full use of edge effects for the rice by
improving ventilation and light penetration, which enhance
photosynthesis, reduce diseases and pests of rice, and deepen the
symbiosis of rice and fish to increase the yields of both crops.
Based on previous experiments, experiments have been initiated using zero tillage
in high ridges, deep trenches, and wheat-rice cropping patterns. This system could
102
RICE-FISH CULTURE IN CHINA
reduce the need for field preparation and trench digging, improve conditions of
water, fertility, atmosphere, and heat, and prevent damage to the soil structure. In
addition, mechanical diggers must be designed to replace manual labour. If
successful, this system could play an important part in improving economic
efficiency.
Development of Rice-Fish Culture with Fish Pits
Feng Kaimao30
The model for rice-fish culture with fish pits was developed as an improvement to
traditional rice-fish culture. It has now become the main type of rice-fish culture
and, in some regions, the major way for farmers to increase their incomes.
China has a long history of rice-fish culture. The traditional method of rice-fish
farming in flat fields faces many conflicts between rice and fish and is easily upset
by changes in natural conditions. Farmers often have to sacrifice the fish to save
the rice, which has diminished the role of rice-fish farming and hindered its
development. Before 1980, rice-fish farming in Dazu County yielded only
22.5-52.5 kg offish per hectare. In 1981, rice-fish farming in flat fields advanced
to some extent, but fish yields were still very low (Table 1).
Before the 1980s, aquaculture scientists in China experimented with fish troughs
combined with fish trenches, which had been adopted in ricefields in the southern
part of Jiangsu Province. However, during the midsummer droughts in Dazu
County, the shallow troughs and small trenches did not provide sufficient water for
the rice and fish. As well, the fish were not able to adapt to the high temperatures
experienced during the drought.
Researchers in Dazu County studied the factors that influenced fish growth, e.g.,
the relationship between temperature and depth of the different water layers, the
upper and the lower limits of temperature that suit fish growth, the relationship
between the appropriate temperature range and the environment of the ricefield, the
quantities of dissolved oxygen produced and consumed during the day and at night,
and the form of oxygen molecules moving in the water. Based on their research,
they developed a new approach to solve the conflicts between fish and rice. They
dug 1-m deep fish pits that covered about 6-8% of the ricefield and connected the
pits to trenches. Field experiments were conducted in many areas between 1980
and 1983. This new model of rice-fish farming was verified and accepted by
farmers and the county government.
Development of the Method
At the beginning of the trials in 1981, the area for rice-fish farming with fish pits
was 0.2 ha. In 1982, the area reached 1.1 ha. Multiple-plot trials totalled 14 ha in
30
Agriculture, Animal Husbandry, and Fish Bureau, Dazu County, Dazu,
Sichuan Province.
104
RICE-FISH CULTURE IN CHINA
Table 1. Fish yields from flat-field rice-fish farming.
Area
(ha x 1000)
Total Yield
(tonnes)
Unit Yield
(kg/ha)
1981
2.7
187
69.0
1982
8.8
977
99.0
1983
10.2
1371
133.5
1984
9.7
1043
106.5
1985
10L5
920
88.5
1983. By October 1984, the area had expanded to 3080 ha, and by the end of
1985, 3570 ha had been developed. Farmers had discovered that the economic
benefits from the new model were 3-8 times greater than from flat field rice-fish
culture. Fish yields as high as 3 195 kg/ha were obtained. From 21 July to
31 August 1985, Dazu County experienced a midsummer drought and 5 800 ha of
flat-field rice-fish farming (58.8% of the total area devoted to rice-fish farming)
were damaged. However, good harvests of both rice and fish were obtained from
rice-fish farming with fish pits. This convinced the farmers of the value of using
the new model and the technique became popular. By the end of August 1986, the
total area of rice-fish culture with fish pits reached 41474 ha. It is expected that
new developments will move toward combining fish pits with shallow ponds.
Results
Aquaculture production in Dazu County from all types of water areas has increased
(Table 2). Rice-fish farming has developed most quickly. Rice-fish farming
includes rice-fish farming with fish-pits and flat field rice-fish farming. In the past
few years, production changes from both types of farming have been remarkable
(Table 3). The fish-pit method shows greater resistance to natural disasters
compared with the flat-field style. Although adult fish yields from the fish-pit
method increased remarkably in 1984-1985, the unit yield of fish from flat fields
decreased, apparently because of the midsummer drought. Since then, the area
devoted to the fish-pit method has increased each year. Fish production from fishpits varies depending on the progress of experiments, demonstrations, and
extension efforts. Actual production levels in 1985 are presented in Table 4.
Although the environment in the fish-pit method is superior to the environment in
the flat-field style, production of adult fish was directly influenced by management
level (Table 5). Large-scale experiments, demonstrations, and extension were
carried out in 1984-1985. Yields decreased as the level of researcher involvement
decreased. Yields were highest in experimental areas and lowest in the extension
areas.
105
PATTERNS AND TECHNOLOGY
Table 2. Aquatic production.
Total Aquatic
Production
(tonnes)
Rice-Fish
Other
(tonne)
(%)
(tonne)
(%)
1981
625
187
29.9
447
70.1
1982
1380
878
63.6
503
36.4
1983
2180
1380
63.3
800
36.7
1984
3295
3425
73.6
870
26.4
1985
3271
2465
75.4
806
24.6
Table 3. Changes in fish yields from two types of rice-fish farming.
Total Yield
Area
(ha)
Fish-Pit
Yield
(t)
Area
(ha)
Yield
(0
Flat-Field
%of
Total
Yield
Area
(ha)
%of
Total
Yield
Yield
(tonne)
1982
8800
878
1.1
0.6
0.1
8799
876.9
99.9
1983
10200
1380
14
8.4
0.6
10186
137.6
99.4
1984
12600
2425
2933
1382
57.0
9667
1043
43.0
1985
13400
2465
2933
1536
62.3
10467
929
37.7
Table 4. Actual fish yields from rice-fish farming using fish pits (1985).
Average Yield (kg/ha)
Over
3750
Number of
households*
3735- 2985- 22353000 2250
1500
2
(0.2)
2
(0.2)
20
(1.5)
23
(1.7)
Area (ha)
0.2
0.1
1.6
2.5
Total yield
(kg)
925
405
376
4302
4625
4050
235
1721
Average
yield (kg/ha)
14851125
1110750
735375
Under
375
67
172
521
560
(5.0) (12.7) (38.5) (41.4)
8
23.7
72.4
9875 23488 41652
1234
991
* Number in parentheses equals percentage of total households.
575
46.1
Total
1367
155
1536 82559
33
534
106
RICE-FISH CULTURE IN CHINA
Table 5. Comparison offish yields from rice-fish culture with fish pits
in different districts.
Experimental
District
Demonstration
District
Extension
District
Area
(ha)
Unit Yield
(kg/ha)
Area
(ha)
Unit Yield
(kg/ha)
Area (ha)
Unit Yield
(kg/ha)
1984
27.1
693
679
534
2255
444
1985
40.5
860
679
768
2255
434
These large-scale areas where used to obtain economic data. The ratios of input and
output in 1984 were 1:2.86 for the flat fields, 1:3.59 for the fish-pit method,
1:3.35 for demonstrations, and 1:3.43 for extension. In 1985, the ratios were
1:2.61, 1:3.98, 1:3.16, and 1:3.23, respectively. Average profits from raising fish
in flat ricefields was CNY1 833/ha, with 92.5% of the profit from rice and 7.5%
from fish in 1984. In 1985, profit was CNY1600/ha with 90.5% from rice and
5.5% from fish. Because of the midsummer drought in 1985, profits decreased by
2%. In ricefields with fish pits, profits (CNY3204/ha with 58% from rice and
42% from fish) were highest from the experimental district. The income from
ricefields with fish pits was 6.3-9.8 times greater than from the flat fields in 1984
and 17.7 times greater in 1985. Practice has proven the remarkable beneficial
results of the new model, and additional developments of this model are expected.
Techniques Adopted in the Rice-Azolla-Fish System with
Ridge Culture
Yang Guangli, Xiao Qingyuan, and He Tiecheng31
The rice-azolla-fish system features an ecological three-dimensional approach to
agriculture. Rice (the main crop), azolla, and fish are combined in a symbiotic
complex. Rice is planted on the ridge, azolla grown on the water surface, and fish
raised in the water. This new farming system was studied between 1984 and 1987.
Experiments were conducted on two plots of land, each with an area of 0.2 ha and
a 6-m2 fish pit. Double-cropping rice was planted in one plot, single-cropping rice
in the other. Each plot was randomly arranged with three replications and planted
with local high-yielding varieties or hybrid combinations of rice and azolla (Azolla
filiculoides orX. caroliniana) (6000 kg/ha). Fish species selected for mixed raising
were grass carp (Ctenopharyngodon idella), tilapia (Oreochromis nilotica), lotus
carp, dull carp, and Hunan crucian carp (Carassius auratus). Growth of rice,
azolla, and fish was recorded. The nutrient content of azolla and fish dung was
determined by standard methods of analysis.
Results and Discussion
Proportion of Ridges to Ditches
Ridge width had a bearing on the yields of rice, azolla, and fish (Table 1). The
yield of double-cropped rice on the 106-cm wide ridge (13 834.5 kg/ha) was 4.1 %
higher than in the control (conventional planting), 5.1% higher than on the 53-cm
ridge, and 2.5% higher than on the 80-cm ridge. The yield of azolla grown on the
water surface between the 53-cm ridges (72 930 kg/ha), was 70.3% higher than in
control, 13.4% higher than between the 80-cm ridges, and 55.6% higher than
between the 106-cm ridges.
Yields of fresh fish increased as ridge width decreased. The yield of fresh fish with
the 53-cm ridges (841.5 kg/ha) was 89.3% higher than the control, 12.2% higher
than with the 80-cm ridges, and 22.2% higher than with the 106-cm ridges.
Therefore, wide ridges favoured rice yields, and the narrow ridge favoured growth
of azolla and fish.
When ridge width was uniform and ditch width was varied, rice yields differed.
With a 40-cm ditch, rice yield was 10462.5 kg/ha, the same as in conventional
31
Soil and Fertilizer Institute, Hunan Academy of Agricultural Sciences,
Changao, Hunan Province.
108
RICE-FISH CULTURE IN CHINA
Table 1. Effect of different ridge widths on yields of rice, azolla, and fish.
Rice (kg/ha)
Ridge
Width (cm)
Early Rice
Late Rice
Total
Azolla
(kg/ha)
Fish
(kg/ha)
53
6463.5
6697.5
13161.0
72931
841.5
80
6750.0
7651.5
14401.5
64320
736.5
106
7072.5
6762.0
13834.5
46875
676.5
Control
6675.0
6616.5
13291.5
42825
436.5
Table 2. Effect of different ditch widths on yields of rice," azolla, and fish.
Rice (kg/ha)
Ditch
Width (cm)
Early Rice
Late Rice
Total
Azolla
(kg/ha)
Fish
(kg/ha)
40
4965.0
5497.5
10462.5
56242
613.5
46
4762.5
5347.5
10110.0
50258
702.0
106
4425.0
4965.0
9390.0
61995
784.5
Control
5175.0
5385.0
10560.0
-
-
" Early rice variety (2106); late rice variety (Wei-You 35); ridge width 53 cm.
planting, 3.5% more than with 46-cm ditches, and 11.4% more than with 53-cm
ditches. Yields of azolla and fish were directly related to increases in ditch width
(Table 2).
Production practices have proven that to determine the proportion of ridges to
ditches for to obtain high rice yields, it is necessary to consider soil fertility, the
characteristics of the rice varieties, whether the proportions favour growth of azolla
and fish, and whether rice, azolla, and fish are well coordinated. In a ricefield in
which rice is planted on the ridges, azolla is grown on the water surface, and fish
are raised in fish pits, the water area of the fish pit should be 5-10% of the total
area of the ricefield.
Best results are obtained if the ridge width is 53-106 cm and the ditch width is
40 cm. On each ridge, 4-8 rows of rice are planted 13-16.5 cm apart to obtain
300 000-375 000 hills of seedlings per hectare. If hybrid rice varieties are used,
plant spacing should be 16.5-20 cm with 3-7 rows on each ridge to obtain
225 000-300000 hills of seedling per hectare.
PATTERNS AND TECHNOLOGY
109
Planting Rice During Different Seasons
When ordinary rice varieties were planted in the early crop season and hybrid rice
varieties were planted in the late crop season, yearly rice yield was 12 925.5 kg/ha
or 1 405.5 kg less than that obtained from two crops of hybrid rice (Table 3).
However, there were no differences in the yields of azolla and fish between
ordinary rice + hybrid rice and hybrid rice + hybrid rice. To increase rice yields,
it is important to determine the proper time for planting hybrid rice varieties in the
early and late crop seasons.
When early- or medium-maturing rice varieties (growth duration 100-110 days) are
used as the early crop, the rice varieties used in the late crop season should be latematuring (growth duration about 120 days). If late-maturing rice varieties (growth
duration 115-120 days) are used as the early crop, the rice varieties used in the late
crop season should be early or medium-maturing (growth duration 100-110 days).
When two crops of hybrid rice are grown in a year, the hybrid combinations used
in the early and late seasons should be all early or medium-maturing (growth
duration about 110 days). If a single crop of medium rice is planted, ordinary rice
varieties or hybrid combinations that are late maturing (growth duration
130-135 days) should be used. Conditions of location, cultivation practice, and soil
fertility should also be considered.
Yields of Fresh Azolla
Annual yields of fresh azolla grown in ridged ricefields that use the rice-azolla-fish
system can reach 113 877-132235 kg/ha. Yields of different azolla species vary.
The yield of A. filiculoides (132235 kg/ha) was 15.5% higher than that of
A. caroliniana. In a mixed culture of A. filiculoides and A. caroliniana, yield
(124417 kg/ha) was between the yield of pure cultures of the two species.
Yields of azolla also varied with different locations (Table 4). In winter
(8 November-16 March), A. filiculoides propagated more rapidly in the hilly
region of Hunan and the yield of fresh azolla reached 47010 kg/ha. On average,
yields doubled in 18.8 days. Yield of A. filiculoides were 59.7% greater than yield
of A. caroliniana. Mixed cultures of these two azolla species, on average, doubled
yields in 19.1 days.
During the spring propagation stage in Changsha, in the hilly region of Hunan,
A. filiculoides also propagated faster than A. caroliniana, and the propagation rate
of mixed cultures was between the rate for pure cultures. In the region along
Dongting Lake in northern Hunan, the yield of A. filiculoides was higher than
A. caroliniana, and the yield of the mixed culture was lowest. Differences in yield
were related to the slow rise in temperature in the spring. In the mountainous
region of southern Hunan, the propagation rate of different azolla species was the
same as in middle Hunan because the temperature rose rapidly in early spring.
110
RICE-FISH CULTURE IN CHINA
Table 3. Effect of the proper arrangement of rice varieties on rice yield.
Yield (kg/ha)
Treatment"
I
Early Rice
Late Rice
Total
6364.8
6567.4
12932.2
6932.6
6092.1
13024.7
Rice-azolla-fish
7291.6
7039.6
14331.2
Control (rice only)
7613.4
7216.5
14829.9
Ordinary rice in early season1*
Rice-azolla-fish
Hybrid rice in late season
Control (rice only)
II
Two crops of hybrid ricec
" Ridge width 53 cm; ditch width 40 cm.
b
Rice varieties used in treatment I: early rice Xiangzao indica I; late rice Wei-You 6.
c
Rice varieties used in treatment II: early rice Wei-You 49; late rice Wei-You 64.
When azolla was grown between ridges, yields of fresh azolla in the mountainous
region of southern Hunan was highest, followed by middle Hunan and northern
Hunan. The rapid temperature rise between May-June in northern Hunan affected
the propagation rate of azolla. In southern Hunan, the day temperature was high
and the difference in temperature between day and night was great, which favoured
growth of azolla.
When azolla was cultured on the ridge to over-summer, no matter where it was
grown (in middle, northern, or southern Hunan), the propagation rate of
A. caroliruana was highest, A. filiculoides was lowest, and the mixed culture was
intermediate. These results reflect the fact that A. filiculoides is unable to tolerate
high temperatures. Therefore, in winter or spring, it is better to grow
A. filiculoides, which can tolerate low temperatures; and in summer or autumn, it
is better to grow A. caroliniana, which can tolerate high temperatures. To
compensate for deficiencies in each species, a mixed culture is recommended.
Yields of Fish
Effect on azolla. Four fish species (grass carp, tilapia, crucian carp, and
lotus carp) were raised with azolla for 110-112 days. The fish species best suited
to the rice-azolla-fish system are grass carp and tilapia (Table 5). Both like to eat
azolla and adapt easily to the ricefield environment. The omnivorous crucian carp
and lotus carp (which are benthic and planktivorous feeders) can be raised in the
ricefield in lower numbers (Table 5). Grass carp and tilapia eat over 60% of their
body weight in azolla each day; whereas, crucian carp and lotus carp eat about 8%
of their body weight in azolla.
Table 4. The speed of propagation of different azolla species in different locations.
Winter
Location
F
Growing Between
Ridges
Spring
II
III
Autumn
Summer
II
III
I
II
III
I
I
A. filiculoides 47010
6.3
18.8
33825
4.5
8.2
33206
A. caroliniana
25380
3.9
30.1
23850
3.2
—
—
Ux mixed
culture
46410
6.2
19.1
25800
3.4
10.8
24144
3.3 12.4
6162
II
III
I
II
III
0.7 43.9
-
-
-
—
—
—
—
0.8 35.4
-
-
-
A. Changsha
4.4 9.0
—
—
4808
—
—
B. Nan County
A. filiculoides -
-
-
18998
2.5
16.2
26249
3.5 12.3
1245
0.2 88.2
26400
3.5 14.5
A. caroliniana
-
-
-
15933
2.1
19.3
23000
3.1 14.0
17499
2.3
17.6
28350
3.8 15.6
Ux mixed
culture
-
-
-
14490
1.9 21.2
20123
2.7 16.0
6162
0.8 35.4
28073
3.7 15.8
TJ
>
H
m
33
C/>
>
Z
C. Guidong
A.filiculoides-
-
-
36449
4.9 8.3 42800
5.7 7.0 29291
3.9 11.5
-
-
-
A. caroliniana
-
-
-
21341
2.8 14.1
43187
5.8 7.0 60110
8.0 5.2
-
-
-
Ux mixed
culture
-
-
-
28605
3.8 10.5
50768
6.8 5.9 43715
5.8 7.7
-
-
-
"1=Yield (kg/ha); 11=Multiplying (-fold); 111=Period of multiplying (days); A=the hilly region in middle Hunan; B=the region along Dongting
Lake in Northern Hunan; and C=the mountain region in southern Hunan.
o
m
O
z
o
r~
O
O
-<
>—»
i—'
•—»
112
RICE-FISH CULTURE IN CHINA
Of the four species, grass carp and tilapia had the highest growth rate. Their body
weights increased 4.2 and 6.2 times, respectively. The body weights of crucian
carp tended to decrease when they grew to a certain stage, and when lotus carp
were fed only azolla, their body weight decreased. The digestibility of
A. filicidoides (18.1%) was higher than A. caroliniana (12.9%) for grass carp and
tilapia, respectively. Therefore, A, filiculoides is a better food for fish than
A. caroliniana.
If it is assumed that fish yield was 750 kg/ha and that the amount of azolla eaten
per gram of fish daily was 0.605 g/day, the amount of dung excreted by the fish
would be 52.9% and it would contained 2.7% N. Therefore, when fish are raised
in a ricefield for 100 days, they provide the ricefield with 85.5-103.5 kg N per
hectare.
Effect of different fish species. When fingerlings bred in spring were
raised, yields of rice and azolla were correlated negatively with the proportions of
grass carp and tilapia, but yields of fish were correlated positively with the
proportions of grass carp and tilapia. To fully use the azolla and the natural
resources of the ricefield, the proportion of fish raised should be 60-70% grasseating grass carp and tilapia and 30-40% omnivorous crucian carp and lotus carp
(Table 6).
Effect of stocking density. When fingerlings bred in spring were raised,
the yields of fish were correlated positively with stocking density. With
30000 fmgerlings/ha, yield of fish was 630 kg, which was 15% higher than the
yield obtained from 15000 flngerlings/ha and 5.6% higher than from
22 500 fingerlings/ha. Therefore, stocking density has an important bearing on fish
yields.
Survival rate of fingerlings (e.g., grass carp) was correlated negatively with
stocking density. At a density of 15000 fingerlings/ha, survival rate was 3% higher
than at 30 000 fingerlings/ha. Increases in body weight of fish followed a similar
trend. When stocking density was 15000 fingerlings/ha, body weight was 11.4 g
heavier than at 22500 fingerlings/ha and 20.6 g heavier than at
30000 fingerlings/ha (Table 7).
Effects of pesticides. In general, pesticides are applied in the
rice-azolla-fish system to control rice pests and diseases. The routine doses of
pesticides such as methamidophos, dimethoat, dichlorphos, chlordimeform,
trichlorfon, MIPC, and kasugamysin did not harm grass carp, tilapia, crucian carp,
and lotus carp. Malathion and EBP were safe for crucian carp and dull carp, but
had lethal effects on tilapia. Phenthoate was harmful to all the fish tested. The
toxicity of various pesticides to fish was in the order: kasugamucin <
methamidophos < trichlorfon < dimethoat < chlordimeform < tetra
chlorvinphos < dichlorphos < malathion < phenthoate (Table 8).
113
PATTERNS AND TECHNOLOGY
Table 5. The total amount of azolla eaten by four fish species (GC grass carp; CC crucian
carp; TL tilapia; and LC lotus carp) and the feed conversion efficiency (CF) (plot area 66
m2; water depth 1.2 m; 30 fish stocked; 30 fish harvested 31 July).
Body
Stocking Weight
Fish
Date
(g/fish)
Body
Weight Days Survival
(g/fish) Raised
Rate
Body
Weight
Increase
(g/fish)
Weight
Increase
(%)
Azolla
Eaten
(g)
CF
GC
9 April
54.7
228.7
112
100
174
5220
25590 49.0
CC
9 April
75.0
110.8
112
100
35.9
1075
33550 31.2
TL
21 April
24.7
163.1
100
100
138.7
4162
217100 52.2
LC
9 April
96.8
92.2
112
76.7
4.6
104.2
17810
0
Table 6. Effect of the proportion of different fish species on yields of rice,
azolla, and fish."
Yield of Rice (kg/ha)
Treatment Species
Early
Late
Total
Yield of
Azolla
(kg/ha)
I
4636.5
6600.0
11236.5
47670
628.5
4761.0
6529.5
11290.5
51975
633.0
4458.0
6301.5
10759.5
59700
568.5
Grass carp 45%
Yield of
Fish
(kg/ha)
Tilapia 25%
Lotus carp 15%
Crucian carp 15%
H
Grass carp 25%
Tilapia 45%
Crucian carp 15 %
Lotus carp 15%
HI
Crucian carp 35%
Lotus carp 35%
Grass carp 15%
Tilapia 15%
* 22 500 fingerlings bred in the spring are raised per hectare; rice variety used in early season
was Zhefu 802; hybrid rice variety used in late season was Wei-You 6; ridge width 53 cm; ditch
width 40 cm.
114
RICE-FISH CULTURE IN CHINA
Table 7. The survival rate of fingerlings raised at different densities and their weight
increase.
Species
Grass carp
No.
No.
Fish
Fish
Fingerlings Raised Harvest
(per ha)
(per ha) (per ha)
15000
Tilapia
Surv
Rate
(%)
Avg
Body
Weight
(g)
Yield
(kg)
2220
1755 79.1
53.4 93.0
2220
1095 49.3
45.2 49.5
Total
Yield
(kg)
Lotus carp
555
450
81.1
61.7 27.0
Crucian
carp
555
450
86.5
64.1
3330
2535
76.1
62.0 106.5
3330
540
16.2
47.2 25.5
Lotus carp
840
630
75.0
54.8 34.5
Crucian
carp
840
705
83.9
51.1 36.0 202.5
4440
2925
65.9
32.8 96.0
Tilapia
4440
1110 25.0
43.2 48.0
Lotus carp
1110
Crucian
carp
1110
Grass carp
22500
Tilapia
Grass carp
30000
615
55.4
1005 90.5
31.5 201.5
Total
Yield
(kg/ha)
535.5
592.5
56.1 34.5
50.8
51.0 229.5
630.0
Conclusion
In a rice-azolla-fish system that includes ridge culture, the ricefield should be
constructed with: ridges 53-106 cm wide, ridge ditches 40 cm wide and 20-25 cm
deep, a main ditch (50 cm wide and 50 cm deep) in the centre of the field, and
deep ditch (50 cm wide and 50 cm deep) surrounding the ricefield. A fish pit
(80-100 cm deep) should occupy 3-10% of the total area of the ricefield. Of the
fingerlings raised in the pit, 3-5% are bred in spring and 8-10% are overwintering
fingerlings. Soybean and melon can also be planted around the pit.
High-yielding rice varieties are used. Two crops of hybrid rice are planted with
wide row spacing and narrow plant spacing to increase the border effect and
enhance the use of light. In a ricefield of ordinary rice, 300000-375 000 hills of
seedlings per hectare (5-7 seedlings/hill) are planted; if hybrid rice is used,
225 000-300000 hills of seedlings per hectare (1-2 seedlings/hill) are planted.
PATTERNS AND TECHNOLOGY
115
Table 8. The safe concentration of different pesticides to four fish species in 72 hours.
Crucian Carp
Pesticides
Tilapia
Dull Carp
Lotus Carp
F
II
I
II
I
II
I
II
Methamidophos
23-30
110
18-22
50
23-27
78.5
18-20
79.5
Dimethoat
25-30
53
23-26
21.2
23-25
53
4049
21-24
6.9
22-25
2.1
23-27
17.6
23-26
10.6
Dichlorphos
25-28
12.9
24-26
9.2
24-30
11.7
22-23
10.7
Tetrachlorvinphos 25-28
25.2
21-23
31.5
21-24
31.5
21-24
25
Trichlorfon
25-28
50
22-24
8.3
Chlordimeform
21-24
55.5
22-24
22.2
23-27
92.5
23-27
22.2
MIPC
23-24
1250
23-30
420
23-27
416
23-25
665
EBP
25-28
6.1
24-26
3
22-27
9
Kasugamucin
21-24 4590
23-25
4440
22-26 2750
23-27
3500
aI = water temperature (°C); II = safe concentration (ppm).
More P and K fertilizers and less N fertilizer are applied in deep placement. Late
rice seedlings can be transplanted without tillage. Attention must be paid to field
management. The water level on the ridge surface should be regulated according
to the growth stage of the rice.
Low-temperature tolerant A. filiculoides and high-temperature-tolerant
A. caroliniana can be grown. In general, 300-500 kg of A. filiculoides are planted
in the field in early or middle March, and 200-400 kg of A. caroliniana are
planted 7 days after transplanting early or medium rice. Mixed culture of these two
azolla species is possible.
Suitable fish species are grass carp, tilapia, crucian carp, and lotus carp. All four
species like to eat azolla, grow rapidly, and adapt themselves to the ricefield
environment. The fingerlings (grass carp and tilapia 60-70%; crucian carp and
lotus carp 30-40%) are released into the ricefield in early May. Generally,
6000-12000 overwintered fingerlings or 30000-45000 fingerlings bred in the
spring are raised per hectare.
Routine dosages of common pesticides are safe to these four fish species. However,
malathion and EBP are lethal to tilapia, and phenthoate is harmful to all of the fish.
This page intentionally left blank
Semisubmerged Cropping in Rice-Fish Culture in Jiangxi
Province
Liu Kaishu,32 Zhang Ningzhen32 Zeng Heng32 Shi Guoan33 and Wu
Haixiang34
Most of the 0.5 million ha of croplands in Jiangxi Province are pit fields, ridged
fields, alluvial fields, and low grounds near the lakeside. These areas make up
about 20% of the total ricefields in Jiangxi, but they are mostly cold, waterlogged,
middle- or low-yield plots. The high water table is mainly responsible for the poor
drainage of accumulated water. Constant water saturation has turned the soil to
gley, which is cold, infertile, acidic, poisonous and lacks oxygen. Under these
conditions, water, nutrients, air, and temperature are unfavourable to the growth
and development of rice. Most regions yield one crop of rice a year, i.e.,
middle-late rice, but yield is low. To transform these low-yielding lands and
increase crop production, a semiarid rice production initiated by Professor Hou
Guangjiong was introduced in 1986 into the mountainous area of Gannan
Prefecture, Jiangxi Province. This method of semisubmerged cropping in rice-fish
culture has been improved to suit local conditions and has increased crop yields.
Main Principles
This method makes drastic changes to the system of rice cropping: planting on
mounds instead of in furrows, putting ridges and ditches side by side to change the
conditions in the field and add an active layer, planting rice on dikes, and culturing
azolla and fish in the ditches. The physical changes raise the temperature of the soil
and water, speed the catabolism of organic matter and the release of nutrients, and
decrease the effect of toxic substances. As a result, seedlings revive sooner after
transplanting, grow quickly, and have more white roots.
This method of rice-fish culture can turn single-crop agriculture into a double or
multiple-harvest system and the slack winter season into a busy time. It is an
excellent model of ecological agriculture that is applicable in all districts.
32
Jiangxi Agricultural University, Nanchang, Jiangxi Province.
33
Agricultural Administration Bureau, Ruijin County, Ruijin, Jiangxi
Province.
34
Land Administration Bureau, Shangyou County, Shangyou, Jiangxi
Province.
118
RICE-FISH CULTURE IN CHINA
Continuous Nontillage
After the topsoil is ploughed for the first time, ridges and ditches are constructed
side by side in the fields. Rice is planted on the ridges and fish are cultured in the
ditches. Thereafter, the topsoil is not ploughed or harrowed to ensure that the
active top layer is not destroyed. The soil does not become a caked mass; it grows
softer with time. If the topsoil is ploughed, pockets of air and water capillaries in
the soil are blocked. This decreases the percolation ratio, destroys the soil structure
and the balance of water, nutrients, air, and temperature, and, as a result, reduces
crop yields.
Continuous Ridge Tillage
Ridge tillage raises both the temperature of the water and soil and the
oxidation-reduction potential of the soil. It activates soil nutrients and reduces toxic
substances. This stabilizes the water, nutrients, air, and temperature and makes
conditions more suitable for the growth and development of rice.
Continuous Infiltration
Capillary water in the soil is the only form of water that contains available
nutrients and can flow freely, aerate the soil, and conduct heat. The key to
semisubmerged cropping is improving the hydrological system of the soil. The
continuous infiltration of capillary water aerates the soil, conveys nutrients, and
prevents the soil from becoming a caked mass. The water level must be controlled
according to the growth of the rice and the needs of the fish.
Demonstration and Application
No Tillage, Rice on the Ridge, Fish in the Ditch
Experiment were carried out for the first time in 1986 in Longhui Village,
Nankang County, Ganzhou Prefecture, in cold, waterlogged mountain fields with
an area of 0.3 ha. In 1987, the area was increased to 2 ha. Experiments were also
carried out in lateritic low-yield plots at Luoding Village, Xingjiang County, and
in a waterlogged lowland area near the lakeside at the Dongfeng Branch Farm of
the Hongxing State Reclamation Farm. The total experimental area in these two
areas was about 1.3 ha. In 1988, the method was popularized in over 1330 ha in
several counties (Ruijing, Nankang, Shicheng, Xingfeng, and Shangyou). In
Ruijing County alone, there were 667 ha. Rice and fish were equally emphasized.
In a few of the experimental plots, azolla was also cultured. The method was
extended by the Agriculture, Animal Husbandry and Fish Department to an area
of 200 ha in the counties of Fuzhou Prefecture.
PATTERNS AND TECHNOLOGY
119
Table 1. Output (kg/ha) of rice-fish culture (rice-on-ridge ROR; rice-on-bed ROB)
compared with output (kg/ha) of conventional flat cropping (CONV). Values of output
expressed as CNY.
Increase
ROR
Rice yield
kg/ha
%
ROB
CONV
kg/ha
%
8673
2223
25.6
7504
6825
680
10.0
Value of rice 3886
3456
430
27.5
2979
2554
425
15.4
Value of fish 2012
0
2012
-
1539
0
1539
-
3456
2442
86.3
4518
2554
1964
75.7
Total value
10896
CONV
Increase
5898
Table 2. Fish output (kg/ha) and economic benefits of two new methods (CNY/ha).
Number of
Households
Fish
Output
Breeding
Cost
Net
Income
Rice-on-ridge, fish-in-trench 8 3333.0 885.0 2448.0
Rice-on-bed, fish-in-trench 6 1288.5 109.5 1179.0
Difference
-
2044.5
775.5
1269.0
Rice on the Bed, Fish in the Ditch
In 1987, this method was demonstrated on 2.8 ha in Shangyon County, Ganzhou
Prefecture. The method features a wide ridge (0.8-1.2 m) that is constructed after
the topsoil is ploughed. Rice is planted 13-17 cm apart on beds in rows that are
20 cm apart; fish and azolla are cultured in the ditch.
Benefit Analysis
Because management of agricultural production is presently carried out by
individual households, the experiments, demonstrations, and applications were
arranged at the household level. During the entire production period, technicians
were sent to the areas to provide technical advice, conduct quality inspections, and
observe and record results. The results are analyzed and compared in Tables 1-3.
Compared with conventional flat cropping, there were considerable increases in
rice output and income from fish whether the rice-on-ridge or the rice-on-bed
method was used. For example, 11 households used the rice-on-ridge method.
120
RICE-FISH CULTURE IN CHINA
Table 3. Comparison of economic benefits of different combinations offish species
reared using the rice-on-ridge, fish-in-trench method.
Area (ha)
Cost
(CNY/ha)
Output Value
(CNY/ha)
Net Income
(CNY/ha)
Grass carp
0.21
199.2
698.4
499.2
Common carp
0.31
38.2
651.0
612.8
Grass carp, common carp,
and silver carp
0.14
889.4
2988.9
2099.5
Grass carp, common carp,
and variegated carp
0.10
501.0
2299.9
1798.9
0.28
1258.4
4190.1
2931.7
Grass carp, common carp,
silver carp, and variegated
carp
Their average rice output increased by 2 223 kg/ha (range 420-7140 kg/ha) and
average net income from fish was CNY2010/ha (range CNY450-4 935/ha). When
the value of the fish and the increased amount of rice were both counted, the total
rate of increase in value was 36.5-216.9% (average 86.3%). In another four
households that used the rice-on-bed method, the increase in rice production was
680 kg/ha (range 530-990 kg/ha) and the net value of the fish was CNY1540/ha
(range CNY531-3 170/ha). The total net value of fish and rice increased by 76%
(Tables 1 and 2).
The rice-on-ridge method is superior to the rice-on-bed method because it improves
the ecological environment of the farmland (and enhances the growth of rice) and
because it has a larger area of water, which is favourable for fish breeding. Higher
economic benefits were obtained from the rice-on-ridge method when mixed
species of fish, instead of a single species, were raised (Table 3).
Soil Improvement
Professor Hou Guangjiong has reported many improvements in the soil using the
rice-on-ridge, fish-in-trench, no-tillage method of semiarid rice cultivation.
Preliminary observations, suggest that unit weight of the soil decreases,
temperature increases, and that the soil contains more organic matter, total
nitrogen, available nitrogen, phosphorus, and potassium (in some cases, there was
a tendency toward less total phosphorus compared with conventional flat cropping)
(Tables 4-6).
PATTERNS AND TECHNOLOGY
121
Table 4. Reduction in soil unit weight (g/cm3) as a result of semiarid fish culture.
Semiarid Fish
Culture
Flat Cropping
Reduction
ZhuLongpeng
1.11
1.21
0.10
ZhuChangrui
0.96
0.98
0.02
ZhuQiusheng
0.84
1.14
0.30
Zhu Xiaoping
0.85
0.93
0.08
ZhuChangfa
0.74
1.01
0.27
LinYuanxiao
0.84
0.95
0.11
LinChuanrong
0.98
1.00
0.02
LinYuanrong
0.97
0.99
0.02
Mean
0.91
1.03
0.12
Household
Remaining Problems
In experiments and demonstrations, the semiarid rice-on-ridge, fish-in-trench
method has remarkably increased production and income and improved soil
conditions. In 1989, the Prefectural Department of Ganzhou planned to apply the
new method on 33 330 ha. Farmers who had become aware of the benefits of the
method were happy. But, to extensively disseminate any new technique, potential
problems should be examined and addressed.
Farmers do not believe that rice can be grown without ploughing the field. For
thousands of years, rice has been planted in water using the flat basin irrigation
cropping method. Ricefields with ridges are new. Most farmers doubt that the rice
plants can absorb water and nutrients when they are planted on the ridges. Some
farmers also complain that the ridges make it difficult for them to put their
threshing tubs and machines in the fields at harvest time. More demonstration and
extension efforts are needed to overcome these problems.
Many places have no previous experience with raising fish in ricefields. There are
also some social problems. Fish in the fields are often stolen, especially in cold,
waterlogged fields that are usually located in remote mountain areas. Farmers
worry about this. Local governments must strictly enforce the law to protect farm
production from theft. The villagers could also develop some protective measures.
The farming activities in the new method (e.g., digging trenches, forming ridges,
clearing mud from the trenches, and applying fertilizer) require much labour. In
Longhui Township, Nankang County, a small iron spade that was light and handy
for clearing mud from trenches was popularized. Labour-saving tools or devices
122
RICE-FISH CULTURE IN CHINA
Table 5. Soil temperatures (°C) at different depths with different cropping systems.
Households
Time
Semiarid Rice and
Fish Culture
Flat Cropping
Differences in
Temperature
0-10
cm
10-20
cm
0-10
cm
10-20
cm
0-10
cm
10-20
cm
Zhu Longpeng
May 11
11:00
24.5
24.2
24.1
23.7
0.4
0.5
May 14
10:00
23.7
23.6
23.4
23.2
0.3
0.4
May 17
10:00
25.0
24.8
24.6
24.5
0.4
0.3
-
24.4
24.2
24.0
23.8
0.4
0.4
May 11
12:00
24.5
24.3
24.0
23.8
0.5
0.5
May 14
11:00
23.9
23.7
23.5
23.2
0.4
0.5
May 17
11:00
25.1
24.9
24.5
24.3
0.6
0.6
May 19
11:00
21.0
20.8
20.5
20.3
0.5
0.5
-
23.6
23.4
23.1
22.9
0.5
0.5
May 11
11:00
25.0
24.8
24.6
24.4
0.4
0.5
May 14
11:00
24.0
23.7
23.5
23.3
0.5
0.4
May 17
11:00
25.1
24.9
24.5
24.3
0.6
0.6
May 19
14:00
21.4
21.3
21.0
20.7
0.4
0.6
-
23.9
23.7
23.4
23.2
0.5
0.5
Mean
Zhu Changgui
Mean
Zhu Changfa
Mean
Table 6. Analysis of soil nutrients (semiarid SA; conventional C).
Organic
Matter
SA
C
Total N
SA
C
Total P
SA
C
Available
N
Available
P
Available
K
SA
SA
C
SA
C
3.11
28.3
29.8
C
(1)'
4.30
3.49 0.146 0.102 0.019 0.012
76.5 64.9
6.69
(2)
4.91 3.34 0.111 0.115 0.007 0.003
51.0 56.9
4.48 3.12
48.3 39.8
(3)
4.62 2.60 0.116 0.094 0.014 0.020
42.2 40.7
5.22 3.37
46.1 41.0
(4)
4.46 3.46 0.165 0.113 0.007 0.016 178.3 92.0
7.70 6.45
54.4 35.4
(5)
3.42
2.79 0.114 0.100
0.013 0.022
87.4 71.7
4.53
3.84
99.1
43.6
(6)
4.30
3.66 0.149 0.138 0.012 0.007
69.5 67.2
4.52 7.44
87.5
49.5
Avg
4.34
3.21
84.2 65.6
5.52
60.6
39.8
0.134 0.110
0.012 0.013
4.56
"Households were (1) Zhu Longbin, (2) Zhu Changrui, (3) Zhu Longze, (4) Zhu Xiaoping,
(5) Zhu Xidi, and (6) Lin Yuan Xiao.
PATTERNS AND TECHNOLOGY
123
for trench digging, ridge forming, and row fertilization need to be developed.
When a new technique is applied in a large area, farmers, because of their different
levels of understanding, sometimes fail to follow the technical requirements for
certain farming activities. Because of this, not only should extension and guidance
be stressed, but input supplies, such as chemical fertilizers and pesticides, must
also be made available.
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Rice-Azolla-Fish Symbiosis
Wang Zaide, Wang Pu, and Jie Zengshun35
Rearing fish and Azolla spp. in ricefields is an important component of traditional
organic farming in China. Rice-azolla-fish symbiosis is a new development in
ecological agriculture. The results of a 2-year field experiment indicate that rearing
fish and azolla in ricefields increases the output of rice, azolla, and fish.
The highest output of rice was obtained from the rice-azolla-fish system
(7096.2 kg/ha). This was an increase of 9.3% compared with the control. The
rice-azolla system had the next highest yield, followed by rice-fish culture and the
control. The coefficient of use of light energy was highest for the rice-azolla
system, followed by rice-azolla-fish, rice-fish, and the control (Table 1).
Output of fish was highest in the rice-African catfish fry field (717.0 kg/ha),
followed by food fish reared in the rice-azolla-fish field (536.3 kg/ha). The lowest
fish output (265.4 kg/ha) was obtained from food fish (Table 2).
The cost of inputs of seed, fertilizer, labour, and fry were compared with the
outputs of rice, straw, and fry. Total net income was highest for the
rice-azolla-fish field (CNY8814.5/ha); an increase of CNY4521.8/ha over the
control. The incomes from the other systems were: rice-fish (CNY7968.3/ha),
rice-azolla (CNY4 637.9/ha), and the control rice plot (CNY4 292.7/ha) (Table 3).
Table 1. Effects of rice-azolla-fish symbiosis on rice output
(CLE coefficient of light energy).
Rice Output (kg/ha)
Treatment
1986
Rice-azolla-fish 5713.5
8478.0
7096.2
602.8
9.3
19877.1
1.12
Rice-azolla
5277.8
8531.3
6904.6
411.1
6.3
20370.0
1.14
Rice-fish
5177.3
8288.3
6732.8
239.3
3.7
14792.5
0.83
Rice (control)
4846.5
8140.5
6493.6
-
14328.0
0.81
35
Average Increase
(%)
Biomass
(kg/ha)
1985
-
Beijing Agricultural University, Beijing, Beijing Municipality.
CLE
126
RICE-FISH CULTURE IN CHINA
Table 2. Effects of rice and rice-azolla-fish on fish growth and output.
Size of
Fish (cm)
Fish
per ha
Fish
Survival
(%)
Weight of
One Fish
(kg)
Output of
Fish
(kg/ha)
Rice-azolla-African fish fry
2.5
22500
62.0
0.023
324.4
Rice-azolla-carp fry
1.5
7500
93.1
0.060
418.7
Rice-azolla-grass carp fry
2.5
22500
61.5
0.020
280.4
Rice-azolla-food fish 1.5 7500 93.2 0.075 536.3
Rice-African fish fry
3.0
11625
84.1
0.073
717.0
Rice-carp fry
2.5
22500
49.0
0.023
249.4
Rice-grass carp fry
3.0
11625
78.6
0.049
450.8
Rice-food fish 2.5 22500 51.5 0.023 265.4
Table 3. Economic effects of rice-azolla-fish symbiosis [RAF rice-azolla-fish; RA
rice-azolla; RF rice-fish; and R rice (control)].
Inputs (CNY/ha)'
Labour Fry Total
Output (CNY/ha)
Rice
Straw
Fry
Total
Net
Income Increase
RAF
1245
120 1879
5765.5
423.9
6000
RA
1080
— 1590
5801.3
426.6
-
6227.9
4637.9
345.2
RF
1245
120 1879
5634.0
414.3
5060
9850.8
7968.3
3675.8
_R
1140
-
5535.6
407.1
-
5992.7
4292.7
-
1650
10689.0 8814.5
4521.9
* All treatments included the following inputs: seed CNY120/ha, chemical fertilizer
CNY352.9/ha, and agricultural chemicals CNY37.5/ha.
The rice-azolla-fish system had obvious economic benefits. In the rice-azolla-fish
system, rice output and net income were higher than the control, and there were
good ecological effects as well. Soil organic matter was highest in the
rice-azolla-fish system (1.4), followed by rice-azolla and rice-fish (1.25) and the
control (1.09). The pH was highest in the control (8.66) and lowest in the other
fields (8.03-8.02). Nitrogen content was the highest in the rice-azolla field
(0.081), followed by rice-azolla-fish, rice-fish, and the control.
127
PATTERNS AND TECHNOLOGY
Table 4. The ecological effects of rice-azolla-fish symbiosis
on the chemical properties of soil.
Organic
Matter
Total
Nitrogen
pH
Total
Salts
Cl'
HC02
Rice-azolla-fish
1.4
0.0771
8.02
0.016
0.008
0.026
Rice-azolla
1.25
0.0810
8.02
0.019
0.008
0.027
Rice-fish
1.23
0.0742
8.03
0.016
0.008
0.028
Rice (control)
1.09
0.0724
8.66
0.042
0.009
0.032
The rice-azolla-fish, rice-azolla, and rice-fish systems improved the physical and
chemical properties of the soil (Table 4), reduced cost, diseases, pests, and weeds,
and avoided environmental pollution.
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Economic and Ecological Benefits of Rice-Fish Culture
Li Xieping, Wu. Huaixun, and Zhang Yongtai36
Research on the economic and ecological benefits of rice-fish culture was
conducted in 1985-1987. The objectives were to more fully exploit agricultural
resources in rural areas and to improve field productivity. A 0.1-ha experimental
field at the Li-Xia-He Regional Agricultural Institute was used. In total, there are
more than half a million hectares in Li-Xia-He where the cropping system is wheat
and rice. In general, the soil is a heavy clay that is low in elevation and has good
water retention. Conditions for rice-fish are good.
Normal hybrid rice (Xian-you 63) and a hybrid (Xian-you 63P, developed by the
Yangzhou Regional Agricultural Institute) were planted under single factorial
designs for 3 years. The variable factors were density, planting pattern, fertilization
strategy, and amount of nitrogen. Experiments were carried out simultaneously in
0.001-ha plots with three replicates, and in 0.04-ha test fields with two replicates.
Two types of cultivation were used, one for fry, the other for mature fish. Each
method of cultivation was subjected to a number of treatments to test the effects of
different proportions offish species, stocking size of fish, and density. A ricefield
without fish was used as the control.
The main fish species used were Fu-shou fish (Oreochromis mossambicus x
O. niloticus Fj), grass carp (Ctenopharyngodon idella), and common carp
(Cyprinus carpio) with a small proportion of bighead carp (Aristichthys nobilis) and
white crucian carp (Carassius cuvieri).
After the fields were ploughed, fish trenches, 0.33-m wide and 0.40-m deep, were
dug in an X pattern. At the cross points of the trenches, two fishponds (each 2.5-m
long, 1-m wide, and 1-m deep) were constructed. The area of the trenches and
ponds was 3.5% of the total area of the field. Fingerlings were stocked in the
ricefield 10-17 days after the rice was planted and were fed mainly azolla and fresh
grass and a small proportion of grain products. For 30 days after stocking, the fish
were fed 4.5-6.0 kg/ha of wheat flour with small amounts of azolla each day.
After 30 days, 7.5-15 kg of grain products and 75-150 g/ha of fresh grass were
fed each day. The amount of feed was increased as the fish grew. The water in the
field was normally kept at a depth of 3-10 cm, but the level was lowered for
several days before differentiation of the rice panicles to dry the field slightly. The
36
Li-Xia-He Regional Agricultural Research Institute, Yangzhou, Jiangsu
Province.
130
RICE-FISH CULTURE IN CHINA
field was drained twice during the filling stage. The control plot was under regular
water management.
The number of rice stems and tillers, the number of weeds, plant and soil nutrients,
and the amount of sunlight penetrating to the bottom of the rice plants were
determined. After harvesting, the ears and characteristics of the rice plants were
measured. The number of fish harvested, their individual weights, and the yields
of rice and fish were determined.
Economic Benefits
Yield of Rice
Yields of rice each year were 9054 kg/ha (1985), 7929 kg/ha (1986), and
7 848 kg/ha (1987) in the control field and 8662, 7884, and 7997 kg/ha in the
ricefield with fish. Rice yields in the field with fish were lower by 4.3% in 1985,
but in 1986-1987, the yields were almost the same. Because the area of fish
trenches and ponds occupied 3.5% of the total area of the field, and the actual
planting area had been reduced by 7.0%, it can be concluded that the yields of
individual rice plants in the rice-fish field increased in 1986-1987. This increase
offset losses from the reduction in planting area; therefore, yields of rice with or
without fish in the field were about the same.
Yield and Value of Fish
In 1985, the average yield of fish from two ricefields was 524 kg/ha valued at
CNY1730/ha. In 1986, despite predation by snakehead fish (Ophiocephalus
argus), the average yield of four plots was 442 kg/ha valued at CNY1750/ha. The
highest yield was 615 kg. In 1987, there was a shortage of fingerlings and
appropriate species, and a large number of fish escaped. The average yield of four
plots was 208 kg/ha valued at CNY989/ha. The highest yield was 300 kg. The
average value of fish for the three years was CNY1490/ha with a net income of
CNY991/ha.
Net Income
The average investment in rice-fish culture was CNY1009/ha. This was CNY406
more than the control and an increase of 67.3%. The reduced use of pesticide and
chemical fertilizer in the rice-fish field lowered costs by 16-25% (1986-1987).
When the increase in yield and the reduced costs are considered, the net income for
the rice-fish field each year was CNY1090/ha (1985), CNY1222/ha (1986), and
CNY796/ha (1987) more than in the control. The average was CNY1036/ha,
which is 40% of the total income from the control (Table 1). These results indicate
that the cultivation of fish in ricefields does not significantly reduce rice yields and
that cost reductions and increases in net income are significant.
PATTERNS AND TECHNOLOGY
131
Table 1. Yield, cost, and net income from rice-fish (1985-1987).
Year
1985
1986
1987
Type of
Field
Yield (kg/ha)
Rice
Fish
Control
9054
-
Rice-fish
8667
525.2
Control
7929
-
Rice-fish
7884
441.8
Control
7998
-
Rice-fish
7996
207.8
Cost (CNY/ha)a
Fish
Net Income
(CNY/ha)
-
2438
516
3528
-
2422
625
3644
636
-
2854
473
353
3650
Rice
459
459
717
601
"Includes insecticide, chemical fertilizer, fingerlings, and fish food.
Ecological Effects
Weed Reduction
In 1985, the ricefields had four species of weeds [wild arrowhead (Sagittaria sp.)
was the main species]. Before the fingerlings were stocked, there were
408.6 weeds/m2 in the control and 519.3 weeds/m2 in the rice-fish field. Twenty
days after the fingerlings were stocked, there were 131.4 weeds/m2 in the rice-fish
field (a reduction of 75%). Although the number of weeds in the control plot
(289.8/m2) also decreased, there were still twice as many as in the rice-fish field.
The weight of the fresh weeds in the control plot was 2 268 kg/ha, which was
5.5 times more than in the rice-fish field. The number of weed species in the
control increased to more than ten.
When the rice plants in the rice-fish field reached the stages of booting and filling,
the lower part of the plants were clean and the surface of the field had only
9 weeds/m2. There were 248.4 weeds/m2 in the control with a fresh weight of
244.8 kg, which was 17 times more than in the field with fish. Before stocking, the
number of weeds in the control increased from 408.6 in 1985 to 501.3 in 1987. In
the field with fish, the number of weeds decreased from 519.03 in 1985 to 176.4
in 1987. Apparently, the cultivation of fish in a ricefield reduces weeds during that
year, and also has long-term effects.
Soil Fertility
The fish in a ricefield can transform insoluble nitrogen in the soil into a soluble
state, which increases soil fertility. Although the control plot used less fertilizer,
the fertility in the rice-fish field improved significantly from 1985 to 1987. The
132
RICE-FISH CULTURE IN CHINA
Table 2. Effects of rice-fish culture on unit weight and porosity of topsoil.
Year
Depth (cm)
1985
0-10
10-20
1986
0-10
10-20
Weight
(g/m3)
Porosity
(%)
Rice-fish
1.378
48.40
Control
1.417
46.82
Rice-fish
1.504
43.32
Control
1.554
41.36
Rice-fish
1.310
50.57
Control
1.279
51.73
Rice-fish
1.462
44.83
Control
1.527
42.38
Type of Field
percentage of organic material in the soil increased from 2.0 to 2.4%, total
nitrogen from 0.14 to 0.16%, soluble phosphorus increased by 76.1%, and
potassium by 20.69%. These results are similar to those reported by the Sanming
Agricultural Research Institute in Fujian Province.
Physical Characteristics of Soil
The stirring movements of the fish aerate the soil and improve its structure.
Vertical sections of the soil at depths of 0-20 cm were tested in 1985 and 1986. In
rice-fish fields, the unit weight of topsoil was 2.1% lower than in the control, and
porosity was greater by 1.2%. This effect was more obvious for subsoil. At depths
of 10-20 cm, the unit weights of soil in rice-fish fields were 3.2 and 4.3% lower
than in the control, and porosity was greater by 2.0 and 2.4% (Table 2).
Losses from Insects
Fish eat insects that float on the water surface and mosquito larvae in the water.
Fu-shou fish and carp jump to catch rice lice (Sogatafurcifera) in the lower stems
of rice plants. In early September (the season during which rice lice emerge), the
number of rice lice per 100 holes of rice was 234 in the control and 424 in the
rice-fish plots. Ten days later, the rice-fish plot had only 42 rice lice, and the
control had 138.1% more lice although insecticide was used in the control.
Therefore, less insecticide can be used in rice-fish fields.
Nitrogen in Rice
The cultivation of fish in the ricefield increased the amount of nitrogen in the soil
and the amount of nitrogen absorbed by the rice plants. In 1987, the total nitrogen
PATTERNS AND TECHNOLOGY
133
Table 3. Effect of planting density on yields of different rice hybrids.
Regular Xian-you 63
Xian-you 63P
1985
1986
1987
Planting density
(lOVha)
37.5
30.0
22.5
15.0
30.0
22.5
28.1
22.5
Control yield (kg/ha)
9315
9051
9105
8543
7638
7929
7917
8081
Rice-fish yield
(kg/ha)
8615
8697
8838
8471
6170
7884
7944
8049
content of rice plants during the booting stage was higher by 35.9% in the field
with fish than in the control field, although the control plot had used 22.7% more
fertilizer. Therefore, in the rice-fish field, more nitrogen is transported to the rice
grains. The nitrogen content of rice from the rice-fish field was 11.2% in 1986 and
10.9% in 1987 (or 0.8% and 1.0% higher than the control). The quality of the rice
in the fields with fish was better.
Factors Affecting Yields of Rice in Rice-Fish Fields
Planting Density
The yield of rice for a specific variety usually correlates positively with planting
density. In practice, the upper limit of density is usually used. However, the same
variety planted in a rice-fish field, would produce a different yield. In an
experiment in 1985, densities within the range of 150000-375 000 holes/ha were
used for hybrid rice. The yield of the control plot increased with density,; whereas,
yield in the rice-fish field decreased. With densities of 300000 holes/ha and
375000 holes/ha, yields from rice-fish fields were lower than the control by 3.9%
and 7.5%; however, the decreases in yield were not statistically significant. Similar
results obtained in 1986 and 1987 (Table 3) indicated that densities of
300000 holes/ha or below did not affect the yield of hybrid rice.
The main reason for this effect on yield is the type of water management used in
the rice-fish field. Taller plants, larger leaves, and longer nodes are produced, and
at high densities, the population becomes too large, which decreases ventilation and
illumination at the bottom of the rice plants. The development of the rice plant is
stunted, which makes it vulnerable to insect pests, diseases, and lodging during bad
weather. In contrast, at relatively lower densities, rice plants grow fast, individuals
are strong, and plants are more resistant to lodging.
Therefore, the appropriate planting density for rice-fish fields is the lower limit for
the variety (usually 10-20% lower than the density used under regular cultivation).
For hybrid rice (Xian-you 63) the following parameters are suggested: distance
134
RICE-FISH CULTURE IN CHINA
Table 4. Ear characteristics of rice under different nitrogen levels
[Treatments (Treat.) C control; RF rice-fish].
Year
Hybrid
1985 Xian-you63
1986 Xian-you63P
1987
Xian-yo63P
Green
Seed
Grains
per Ear
(%)
1000Grain
Weight
(g)
Yield
(kg/ha)
Treat.
Nitrogen
(kg/ha)
Number of
Grains per
Ear
C
218
152.2
91.4
29.8
9054
RF
218
153.3
89.1
29.1
8667
C
280
142.6
87.9
28.2
7929
RF
226
138.3
87.6
28.6
7884
C
275
152.7
83.6
28.9
7998
RF
224
152.5
82.6
28.8
79%
between rows (26-33 cm), distance between holes (11-13 cm) with
270000 holes/ha and 1200000-135000 stems and tillers per hectare. As the rice
grows, the highest number of stems and tillers will reach 3 900 000/ha and there
will be 2400000-270000 ears/ha. This planting density produces a good
population structure, well-developed individuals, and high yields.
Fertilizer
If the amount of fertilizer used for regular cultivation is used in rice-fish fields, it
will upset the carbon-nitrogen ratio and reduce soil fertility, weight per
1000 grains, and yield. For Example, in 1985, the same amount of fertilizer was
used in both the control and the rice-fish field. Grain-seed percentage decreased
by 2.3%, weight per 1000 grains by 0.7 g, and yield by 4.3%.
In 1986 and 1987, the amount of fertilizer applied in the rice-fish field was 19.2%
and 18.5% less than in the control. The grain-seed percentage, average weight per
1000 grains and yield were about the same as in the control. However, the level
of nitrogen was 22.8% higher in rice from the rice-fish field. To achieve high and
stable yields of rice from rice-fish, 20% less fertilizer should be applied (Table 4).
The strategy for rice-fish culture is low planting density, less fertilizer, a small
population, and strong individuals. Improved ecological conditions (ventilation and
illumination) prevent lodging and help produce larger ears, heavier grains, and
high and stable yields.
PATTERNS AND TECHNOLOGY
135
Factors Affecting Fish Yield
Species
In 1985, the effects of mature fish and fry were compared. Mature fish grew
quickly and individual weights at the time of harvest reached 79.3 g for grass carp,
60.0 g for common carp, and 76.9 g for Fu-shou fish. The largest individual
weighed 150 g. White crucian carp, however, grew slowly (individual weight only
28.4 g) although the same size fmgerlings were used for all species.
The fry were small and the densities high, but results were about the same as for
mature fish. Average individual weights of grass carp, common carp, and Fu-shou
fish were 3-5 times greater than white crucian carp and bighead carp (Table 5).
Grass carp, common carp, and Fu-shou fish are the ideal species for rice-fish
culture because they adapt easily and produce high yields. However, bighead carp
and white crucian carp grow slowly and should only be used in small proportions.
Stocking Density
Yield correlates positively with stocking (Table 6). In 1986, two parts of the
rice-fish field (A and B in Table 6) were used. There were 56.9% more fish in A
than in B; 26.3% more fish were harvested from A, and yield increased by 37.6%.
There were 65.9% fry in A than in B; 4.1% more fry were harvested from A and
yield increased by 45%. Results were about the same in 1987 except that
percentage yield increased. For densities of between 4500 and 18000 fish/ha,
yields increased with density (regression equation of y = 0.370 -I- 0.0312 x\ where
y = yield of fish per hectare and x = number of fish harvested per hectare;
r = 0.9778). Higher densities inhibits the development of individual fish.
Stocking Size
Stocking size has a significant effect on individual weight gain during one season.
Experiments using different densities and species, showed that the larger the
fingerlings, the higher the individual weight gain (Table 7). When the stocking size
offish was increased from 4.0-5.0 cm to 8.3 cm in 1985 and from 6.6 cm to 8.3
cm in 1986, average individual weight increased by 131.4% (1985) and 18.8%
(1986). In 1987, stocking size was 4.0 cm and individual weight was only 34 g,
or 40% of the weight of the 8.3-cm individual fish stocked in the previous two
years. The performance of grass carp and common carp were similar to that of Fushou fish. Increases in stocking size increase individual weight and improve the
final yield of fish.
Discussion
Rice-fish culture is a feasible and efficient way to improve the use of agricultural
resources. It improves soil fertility, reduces damage from weeds and insects (and
therefore reduces costs for insecticides and chemical fertilizers), and improves the
quality of rice. With a stocking rate of 15 000-30000 fingerlings/ha, the rice yield
136
RICE-FISH CULTURE IN CHINA
Table 5. Individual weights at harvest of different fish species stocked at different
densities.
Type of
Cultivation
Stocking
Density
(fish/ha)
Harvest
(fish/ha)
Size of
Young Fish
(cm)
6870
5430
8.2
76.9
870
915
5.9
79.8
1860
1965
8.2
28.4
—
420
6.6
60.0
7320
5835
4.0-5.0
27.8
22110
8565
4.0-5.0
22.7
Common carp
7320
3390
4.0-5.0
38.7
White crucian carp
4200
5910
2.6-3.3
6.7
Bigheadcarp
3720
6375
5.0
8.4
Species
of Fish
Mature fish Fu-shou
Grass carp
White crucian carp
Common carp
Fry
Fu-shou
Grass carp
Individual
Weight
(g)
Table 6. Fish yields at different stocking densities.
Type of
cultivation
Year
Field
Stocking
Density
(fish/ha)
Harvest
(fish/ha)
Yield
(kg/ha)
Mature fish 1986 A 24945 7425 420
1987
Fry
1986
B
15900
5880
305
A
18000
9375
286
B
11580
7560
246
C
11220
3690
130
D
4500
5430
168
A
41490
12915
615
B
25000
9120
424
137
PATTERNS AND TECHNOLOGY
Table 7. Effect of different stocking sizes on weights of individual fish.
Species
Year
Stocking
Size
(cm)
Fu-shou
1985
8.2
90-91
142.5
50.0
83.0
4.0-5.0
90-91
74.0
14.8
35.9
8.2
90-94
112.1
37.0
82.4
6.6
90-94
109.1
30.1
69.4
4.0
103
62.3
19.9
34.0
4.0-5.0
90-91
83.7
26.5
42.7
1986
4.0
90-94
83.8
11.9
28.1
1985
5.9
90-91
148.8
15.6
78.7
4.0-5.0
90-91
63.0
20.0
34.0
2.6-4.0
90-94
68.4
11.4
28.3
1986
1987
Common carp 1985
Grass carp
1986
Growth
Period
(days)
Individual Weight (g)'
Largest
Smallest
Average
" From 40 randomly selected individuals.
is 7500 kg, fertilizer can be reduced by 37.5-75 kg/ha N, and 7.5 kg/ha less
herbicide can be used. As a result, net income can be increased by over
CNY750/ha.
To ensure good rice yields from rice-fish fields, planting density should be
lowered and less fertilizer should be applied. This helps develop a plant population
with strong individuals and minimizes shading and lodging. Strong seedlings
should be plated at a density that is 10-20% lower than the density used in a
regular fields. Nitrogen fertilizer should be reduced by 20%; 85-90% should be
applied early in the growing season, and the rest applied during later stages. The
fish species should be adaptable, resistant, high-yielding, and be able to tolerate
heavy doses of fertilizer.
The difficulties in rice-fish culture are the limited growth period, the small amount
of water, changes in water levels, and unstable ecological conditions. To achieve
high yields, it is important to choose the appropriate fish species and to use the
proper stocking density and size. Grass carp, common carp, and Fu-shou fish are
ideal species for rice-fish culture. They should be used as the main species are be
combined with small proportions of other species. To produce mature fish,
70-80% Fu-shou fish and 20-30% grass carp and common carp should be used.
For fry, 80% grass carp and common carp and 20% Fu-shou fish are
recommended.
138
RICE-FISH CULTURE IN CHINA
To produce 750 kg fish/ha, the stocking density should be 1200015000 fingerlings for mature fish and 30000-37500 fmgerlings for fry. It is best
to use large fingerlings. To produce mature fish, the stocking size should be greater
than 6.3 cm for Fu-shou fish and 4.3-6.3 cm for grass carp and common carp.
Although productivity of the individual rice plants was enhanced when fish were
raised in the ricefield, the yield per unit area remained about the same. The
improvement in the quality of the individual rice plants compensated for the
reduced planting area. Results from this study show demonstrate that rice-fish
culture maintains rice yields at the same level as regular cultivation. In contrast to
other reports, this study did not find a tendency for rice-fish culture to increase
yield.
Cultivating Different Breeds of Fish in Ricefields
Wang Banghuai37 and Zhang Qianlong38
Experiments were conducted in Shanggao, Shangyou, and Shuichuan Counties in
1985-1986 to study the adaptability of certain breeds of fish to ricefields.
Experiments were carried out simultaneously in double-cropped ricefields in three
separate villages. Soil fertility was poor in one village, average in one, and good
in another. At each site, the experiment was replicated. The method of rice-fish
culture with trenches and ponds was used at all three sites. The trenches and ponds
took up 4-10% of the total area of the ricefield.
In 1985, each site had 30 ricefield plots and a total area of 1.3 ha. In 10 plots
(0.05-ha each), the fish breeds were cultured separately (monoculture) and given
no supplemental food. In 10 plots (0.003-ha each), the fish were cultured
separately and given supplemental feed. In the final 10 plots (0.06-ha each),
different polyculture mixtures of fish were given supplemental food (single
replicate per trial).
The polyculture mixtures contained nile tilapia, (Oreochromis niloticus), grass carp
(Ctenopharyngodon idella), silver crucian carp (Carassius auratus), local carp, and
six other local breeds. In one trial, equal quantities of each breed was used
(200 fish per breed). In the unequal mixed cultures, the main species (one of nile
tilapia, grass carp, silver crucian carp, or local carp) made up 50% (1000 fish) of
the total number offish raised. Chub and variegated carp made up 2.3% (45 fish)
each, and the other seven fish species made up 6.5% (130 fish).
Culture of Different Fish Breeds
The breeds chosen for culture were fish that could grow to 3-4 cm in length in that
year. Ten breeds of seven fishes were selected: nile tilapia, grass carp, silver
crucian carp, local breeds of red carp (Xingguo red carp, pouch red carp, and glass
red carp), shortnose catfish, chub carp, and variegated carp. The three red carps,
the silver crucian carp, and the shortnose catfish were distributed by the local
government; the other breeds were produced on-site. The fish were stocked before
the end of May, except for nile tilapia, which were put into the ponds from late
May to early June.
37
Aquatic Products Department, Jiangxi Provincial Bureau of Agriculture,
Animal Husbandry, and Fisheries, Nanchang, Jiangxi Province.
38
Agriculture, Animal Husbandry, and Fisheries Department, Yichuan
Prefecture, Yichun, Jiangxi Province.
140
RICE-FISH CULTURE IN CHINA
Table 1. Results of monoculture of 10 fish breeds.
Without Feeding
With Feeding
Average
Survival Unit
Rate
Yield
(%)
(kg/ha)
Survival Unit
Rate
Yield
(%)
(kg/ha)
Survival
Rate
(%)
Unit
Yield
(kg/ha)
Niletilapia
14.3
247.5
51.6
364.5
33.0
306.0
Grass carp
29.3
193.5
41.9
412.5
35.6
303.0
Silver crucian carp
36.7
165.0
52.4
162.0
44.6
163.5
Local carp
37.8
223.5
50.7
310.5
44.3
267.0
Xingguo red carp
30.7
228.0
40.8
309.0
35.8
268.5
Pouch red carp
9.3
241.5
54.6
298.5
32.0
270.0
Glass red carp
25.2
159.0
49.7
415.5
37.5
288.0
Short-nose catfish
0
0
0
0
0
0
Variegated carp
7.1
69.0
8.6
150.0
7.9
109.5
Chub
20.1
120.0
50.6
342.0
35.4
231.0
Average
21.1
165.0
40.1
276.0
30.6
220.5
Lime was used to sterilize the ricefield before the fish were stocked. The main fish
fed was natural food in the ricefield; however, concentrated feeds, such as fine
chaff, wheat bran, and rapeseed cake, were added as needed.
The rice plants were grown and managed in the same way as rice in fields without
fish. Although the area for growing rice was reduced because of the fish trenches
and ponds, rice yields were not reduced because rice was planted along the edges
of the trenches and ponds. When fertilizers or pesticides were applied or when the
field was sun-dried, the fish were drawn into the trenches or ponds. The ricefields
with fish did not need weeding.
All plots were inspected during the last 2 weeks of October. Each fish species was
counted, weighed, and measured, and field management notes were examined
(Tables 1-3).
Adult Fish Culture in Ricefields
In 1986, eight breeds were cultivated in the three sites (silver chub and shortnose
catfish were not used). The number of plots was decreased from 30 to 24, and the
area was decreased from 1.3 ha to 1 ha. Eight plots were used for monoculture
PATTERNS AND TECHNOLOGY
141
Table 2. Results of equal-quantity mixed culture (with feeding) for 10 fish breeds.
Survival Rate (%)
Unit Yield (kg/ha)
Nile tilapia 23.8 39.0
Grass carp
35.7
124.5
Silver crucian
53.0
24.0
Local carp
53.6
117.0
Xingguo red carp
27.1
31.5
Pouch red carp
15.7
7.5
Glass red carp
21.4
61.5
0.5
4.5
Variegated carp
57.5
27.0
Chub
70.8
82.5
Average
35.9
Short-nose catfish
Total
519.0
with and without feeding (without replicate experimental plots). The area of each
plot was the same as in 1985. Two plots were used for equal-quantity mixed
culture with feeding; the rest were used for 3-breed mixed culture with feeding (the
three breeds were nile tilapia, grass carp, and local carp). Each breed was
cultivated separately as the main breed in two plots using the same techniques used
in 1985. For each breed, 4500 fish/ha were stocked in the ricefield. In equalquantity mixed culture, 562 fish of each breed were stocked per hectare (each
breed made up 12.5%). In unequal-quantity mixed culture, 2250 fish were stocked
per hectare: 50% of the main breed plus 7% chub, 3% variegated carp, and 20%
each of two other breeds. Breeds cultivated the previous year were harvested at a
length of 10 cm, and stocking was completed by early May. Results are presented
in Tables 4-6.
Results
Growth of Different Breeds (1985)
Nile tilapia. Even without feeding, high unit yields were obtained when
nile tilapia was monocultivated or used to supplement mixed cultures. Survival
rates, however, were not high because the fmgerlings were small when stocked.
Grass carp. Survival rates were average; however, when grass carp were
used to supplement mixed cultures, survival was high. Unit yield was low in
monoculture without feeding. With feeding in both monoculture and mixed
cultures, yields were higher than for other breeds.
142
RICE-FISH CULTURE IN CHINA
Table 3. Results of unequal-quantity mixed culture (with feeding) for 10 fish breeds
(SR survival rate; UY unit yield).
Nile Tilapia
as Main
Fish
Grass Carp
as Main
Fish
Silver
Crucian Carp
as Main Fish
SR
UY
(%) (kg/ha)
SR
UY
SR
UY
(%) (kg/ha) (%) (kg/ha)
Local Carp
as Main
Fish
Average
Proportion
of Fish
Breeds
SR
UY
(%) (kg/ha)
SR
UY
(%) (kg/ha)
Niletilapia
18.6
241.5
60.3
94.5
29.8
45.0
34.2
51.0
41.4
63.0
Grass carp
33.9
45.0
23.9
111.0
43.2
147.0
59.0
96.0
45.4
96.0
Silver crucian 66.5
19.5
39.8
15.0
53.3
99.0
55.7
48.0
54.0
27.0
Local carp
38.8
52.5
39.6
48.0
48.9
25.5
45.2
129.0
42.5
42.0
Xingguored
carp
30.2
21.0
24.2
25.5
43.8
9.0
22.3
18.0
30.1
18.0
Pouch red
carp
24.0
6.0
13.0
7.5
35.0
13.5
25.9
6.0
24.5
9.0
Glass red
carp
16.0
48.0
19.7
36.0
20.5
51.0
29.5
58.5
21.4
48.0
Short-nose
catfish
1.0
4.5 0
0
0
0
0
0
0.3 1.5
Variegated
carp
43.2
12.0
56.5
15.0
55.0
21.0
52.8
24.0
51.9
21.0
Chub
45.9
13.5
73.2
27.0
88.9
31.5
77.5
39.0
71.4
28.5
Average
31.8
Total
35.0
313.5
41.8
25.3
40.2
442.5
38.3
469.5
354.0
Average survival rate = 37.2%
Average unit yield = 402.0 kg/ha
Silver crucian carp. Survival rates were usually higher than for other
breeds, but because the fish took longer to grow and body size was small, unit
yields were low.
Local carp. Survival rates were high. Unit yields were high in mixed
cultures. When local carp were used as the main breed in mixed cultures, unit yield
was higher than for any of the other nine breeds. In monoculture, yields were low.
143
PATTERNS AND TECHNOLOGY
Table 4. Results of monoculture experiment.
Without Feeding
With Feeding
Average
Survival
Rate
(%)
Unit
Yield
(kg/ha)
Survival
Rate
(%)
Unit
Yield
(kg/ha)
Survival
Rate
(%)
Unit
Yield
(kg/ha)
Niletilapia
53.5
265.5
98.1
393.0
75.8
330.0
Grass carp
49.0
348.0
69.4
639.0
59.2
493.5
Local carp
53.0
273.0
74.8
423.0
63.9
348.0
Xingguo red carp
64.2
208.5
79.8
339.0
72.0
274.5
Pouch red carp
34.1
330.0
42.6
240.0
38.4
285.0
Glass red carp
54.5
280.5
43.9
240.0
49.2
261.0
Variegated carp
72.9
153.0
64.9
231.0
68.9
192.0
Chub
67.5
133.5
62.4
199.5
65.0
166.5
Average
56.1
249.0
67.0
337.5
61.6
294.0
Table 5. Results of equal-quantity mixed culture with feeding.
Survival Rate (%)
Unit Yield (kg/ha)
Nile tilapia 94.7 75.0
Grass carp
70.7
108.0
Local carp
52.9
63.0
Xingguo red carp
63.8
45.0
Pouch red carp
21.5
30.0
Glass red carp
40.9
43.5
Variegated carp
56.9
39.0
Chub
64.8
48.0
Average
58.3
Total
451.5
Pouch red carp. In monoculture or mixed culture, survival rate and unit
yield were low.
Xingguo red carp. In monoculture without feeding, both survival rate and
yield were fairly high, but in mixed culture, both survival rate and unit yield were
rather low.
144
RICE-FISH CULTURE IN CHINA
Glass red carp. Survival rates and unit yields were high in monoculture.
In mixed cultures, survival rates were low, but unit yields were high.
Shortnose catfish. Survival rates and unit yields were low because the
fingerlings used were small. Outside the experimental sites, some farmers stocked
larger fingerling and obtained good harvests.
Variegated carp. In monoculture, survival rates and unit yields were the
lowest of any breed. In mixed cultures, unit yields were low, but survival rates
were high.
Chub. In monoculture, survival rates and unit yields were low. In mixed
cultures (in the proportion 2.5-6.5%), survival rates and unit yields were the
highest among the 10 breeds. Chub also grow fast.
Stocking Methods
Survival rates were lower in monoculture (30.6%) than in mixed cultures (36.6%)
and lower in monoculture without feeding than in monoculture with feeding.
Survival rates in equal-quantity mixed cultures were slightly lower than in unequalquantity mixed cultures. For example, when used as the main breeds in mixed
cultures, survival rates were: silver crucian carp > local carp > grass carp > nile
tilapia. In mixed cultures, the survival rate of the main breed was usually lower
than when that breed was used to supplement other breeds either in unequalquantity mixed culture or in equal-quantity mixed culture.
Unit yields were lower in monoculture without feeding (16.5 kg) than in
monoculture with feeding (276 kg); lower in monoculture with feed (276 kg) than
in mixed cultures with feed (460.5 kg); and lower in unequal-quantity mixed
cultures (354 kg) than in equal-quantity mixed cultures (519 kg). In unequalquantity mixed culture, unit yields were: local carp > silver crucian carp > grass
carp > nile tilapia.
Growth of Different Breeds (1986)
Nile tilapia. Fingerlings can be bred in the ricefield. In monoculture
without feeding, the survival rate was not high, but in the other culture methods,
survival rates were higher than for other breeds. Unit yields, however, were lower
those for grass carp and local carp.
Grass carp. Survival was low, especially when grass carp were cultivated
as the main breed in mixed culture without feeding. Unit yields were highest with
most culture methods.
Local carp. Survival rates were higher than grass carp in most cases, but
were lower than grass carp in equal-quantity mixed cultures with feeding. Unit
yields were lower than grass carp with most culture methods.
145
PATTERNS AND TECHNOLOGY
Table 6. Results of unequal-quantity mixed culture with feeding.
Nile Tilapia
as Main Breed
Grass Carp
As Main Breed
Local Carp
As Main Breed
Average of
Supplementary
Breeds
Survival Unit Survival Unit Survival Unit Survival Unit
Rate
Yield
Rate
Yield
Rate
Yield
Rate
Yield
(%)
(kg/ha)
(%)
(kg/ha)
(%)
(kg/ha)
(%) (kg/ha)
Niletilapia
59.5
174.0
67.6
57.0
89.1
127.5
78.4
91.5
Grass carp
29.5
105.0
36.1
291.0
41.0
106.5
35.3
106.5
Local carp
51.8
120.0
54.4
66.0
58.8
192.0
53.1
93.0
Variegated
carp
65.0
37.5
67.6
40.5
48.0
27.0
60.2
34.5
Chub
62.0
60.0
80.5
61.5
85.1
78.0
75.9
66.0
Average
53.6
Total
61.2
496.5
64.4
516.0
60.6
531.0
391.5
Average survival rate of all breeds
59.7%
Average unit yield 34.6%
Average survival rate of main breeds
51.4%
Average unit yield of main breeds 14.6%
Xingguo red carp. Survival rates were the highest of the four carp breeds,
but unit yields were lower than local carp. In monoculture without feeding, unit
yield was lower than pouch red carp and glass red carp.
Pouch red carp. Survival rates were the highest. Unit yields were low in
mixed culture, but fairly high in monoculture, especially in monoculture without
feeding.
Glass red carp. In monoculture without feeding, survival rates and unit
yields were high. In monoculture with feeding as well as in mixed culture, survival
rates and unit yields were low.
Variegated carp. Survival rates were fairly high, especially when
cultivated without feeding. Unit yields, however, were low.
Chub. Survival rates were fairly high, but unit yields were low. In
monoculture, survival rates and unit yields were lower than variegated carp. In
equal-quantity mixed culture, both survival rate and unit yield were higher than
variegated carp.
146
RICE-FISH CULTURE IN CHINA
Stocking Methods
Survival rates in monoculture (61.6%) were slightly higher than in mixed cultures
(59%) and lower in equal-quantity mixed cultures than in unequal-quantity mixed
cultures. When cultivated as the main breeds in three kinds of unequal-quantity
mixed culture, survival rates were nile tilapia > local carp > grass carp.
Unit yields in monoculture (19.6 kg) were much lower than in mixed cultures
(32.4 kg); lower in monoculture without feeding than in monoculture with feeding;
and higher in unequal-quantity mixed culture than in equal-quantity mixed culture.
The unit yields of the three breeds cultivated as the main breeds in unequal-quantity
mixed culture were ranked from lowest to highest as follows: grass carp > local
carp > nile tilapia.
Discussion
The 2-year experiment on rice-fish culture was conducted under natural conditions
(e.g., floods, droughts, and birds) and certain artificial factors (e.g., management
level of staff, funds, the quality of fish breeds). It involved 50-60 farmers and was
carried out in several sites in three counties, one in the South, one in the North,
and another in the centre of Jiangxi Province. A lead group and a technical group
were organized to undertake the experiment on the basis of unified leadership,
unified planning, and unified standards. Limitations in the experimental methods
included differences between sites in soil fertility, biological resources, water
temperature, water quality, and water sources. There were also differences in ricegrowing skills, management level, stocking, and time of harvest.
Conclusion
The fish breeds best suited to rice-fish culture are grass carp, common carp, and
nile tilapia. These breeds can be used as the main breeds for rice-fish culture. The
breeds most suitable for use as supplementary breeds in rice-fish culture are
crucian carp (mainly silver crucian carp), local red carps, chub, and variegated
carp. Shortnose catfish can be used as a commodity fish under certain conditions.
In this method of rice-fish culture, trenches and ponds occupy 6-8% of the total
area of each plot. The trenches should be 0.35-m deep and the pond 1-m deep.
Rice-fish culture can be carried out while a stable increase in rice yield is
maintained. Fish yields of 450-600 kg/ha of adult fish and 150-225 kg/ha of fry
can be obtained.
Rice-Fish Culture in Ricefield Ditchponds
Luo Guang-Ang39
Rice-fish culture has been traditionally practiced in rural areas. Modern rice
cultivation techniques such as intercropping, fertilizers, and chemical sprays often
conflict with fish growth. In addition, other problems such as monoculture of fish,
delays in putting fish into the pond, short growing periods, and lower output and
economic profits have arrested the development of rice-fish farming. Recent
reforms in the economic system have sparked new initiatives in agricultural
production.
Renewed interest in rice-fish culture has prompted scientists to study different
patterns of rice-fish culture (e.g., ditch-and-pit, wide ditches, and ditchponds).
Research suggests that rice-fish culture in ditchponds can eliminate the conflicts
between fish and rice and take full advantage of the symbiosis between rice and
fish.
Rice-fish culture in a ditchpond is a three-dimensional agricultural production
system. The artificial ecosystem simulates the biostructure of the natural ecological
system and consists of an economic crop (rice) and a commercial animal (fish).
The system provides the high output of an intensive fishpond farming system and
makes full use of the ecological conditions in the ricefield. Fish feed on the
abundant aquatic organisms and coexist with the rice. Both fish and rice develop
harmoniously, each promoting the growth of the other, and problems between fishrearing and field care can be reasonably handled. Both crops can achieve their full
productive potential. At the same time, liana can be grown on an awning above the
pond, taro and beans can be grown on the bank, duckweed can be cultivated with
the fish in the water, and loach can be grown in the mud. This integrated and
intensive farming system produces higher yields of rice, fish, and vegetables.
Management Techniques
The pond, which takes up 5% of the field area, is dug to a depth of 1-1.5 m on
one side of the ricefield. On a third of the pond, a shed with an awning is built.
Ditches are dug 40-60 cm wide and 20-30 cm deep. The ditches are dug according
to the size of the field: if the field is less than 0.07 ha, ditches are dug in a straight
line; if the field is about 0.07 ha, ditches are dug in the shape of a cross; and if the
field is larger than 0.14 ha, parallel ditches are dug in both directions (in the shape
of a double cross).
39
Bureau of Agriculture, Animal Husbandry, and Fisheries, Shangyou,
Shangyou County, Jiangxi Province.
148
RICE-FISH CULTURE IN CHINA
Engineering Construction and Management
Five basic steps are undertaken.
•
•
•
•
•
Select a suitable field. The soil must be fertile, have moderate
texture, and hold water well. The water supply must be adequate
and drainage and irrigation must be available to ensure stable yields
during droughts or excessive rain.
Construct a bank around the field. The bank is raised to a height of
50-70 cm and a width of 30-40 cm. The bank must be solid enough
to withstand heavy rains.
Install fish screens. A semicircle of fish screens about 0.8-m high
and 1-m wide are installed in the water inlets and outlets. The gaps
between fish-screen bars should be 0.3-0.4 cm. A screen with a gap
of 1.5-2.5 cm is placed at the juncture of the ditch and pond to
prevent large fish from damaging rice seedlings. This screen is
removed after the rice heads.
Monitor water and fertilizer. Water and fertilizer have a significant
effect on the growth of fish and rice. Excess nitrogen makes rice
seedlings spindly and results in the closing of crop rows too early
and densely, which is fit for neither fish nor rice growth. Therefore,
the amount of base manure, potassium, and phosphorus fertilizer
should be raised but nitrogen should be controlled to prevent the
rice from becoming spindly. Water management is also important.
Irrigation and drainage should be controlled separately. The water
level should be kept at a depth of 1-1.2 m in the pond; however,
the water in the ricefield should be 5-10 cm deep before rice
tillering and 10-16 cm deep after rice tillering. When pesticides and
fertilizers are needed, the water level in the field should be lowered
slowly and the fish should be driven into the ditch and pond to
separate the fish and rice for a short period.
Patrol fields. Care is required to identify and deal with problems
such as drought, waterlogging of the fields, diseases, insect pests,
escapes of fish, and theft.
Improvements in Culture Techniques
To improve rice-fish culture ditch ponds, several changes are needed in traditional
techniques.
•
•
Transform monoculture into polyculture. Traditionally, common
carp are the only fish grown in the ricefields. However, now many
other species are available, e.g., local carp, wuyuan pouch red
carp, wang-an glass red carp, xingguo red carp, feng carp, mirror
carp, grass carp, black carp, silver carp, big-head carp, nile tilapia,
and crucian carp.
Change from single-cropping to double cropping of fish. Traditional
systems of rice-fish production raised fish once a year However,
PATTERNS AND TECHNOLOGY
•
•
•
149
new techniques now mean that fish can be grown in ricefields
throughout the year.
Institute earlier stocking of fish. In traditional systems, the fish are
stocked after the rice heads. New techniques allow the fish to be
stocked after the rice is transplanted because of the ponds and
ditches in the ricefield.
Increase stocking density of fish. In the past, less than 1500 fish
were stocked per hectare of rice-fish field. Currently,
15 000-30000 fish per hectare are used. The density depends on the
objective of the rice-fish system. For fish fry, the density of
summer fry is usually 19500-30000 fish/ha; for food fish,
6 000-9 000 spring fish fmgerlings per hectare are recommended.
In both cases, grass carp, common carp, and nile tilapia make up
about 90% of the total and black carp, silver carp, bighead carp,
and crucian carp make up about 10%.
Introduce feeding of fish. Water plants, plankton, and aquatic
animals in the ricefield were the traditional sources of food for the
fish. Green grass, duckweed, algae, rice bran, bean residue,
distillers' grains, and manure are now added to supplement the feed
for the fish.
Integrated Management
In addition to fish and rice, diverse agricultural products can be obtained from
ricefields. For example, soybean, peppers, tomatoes, sorghum, corn, taro, mustard
can be grown on the banks; vine crops such as musky pumpkin, wax gourd, balsam
pear, Lagenaria vulgaris, and cow gram can be grown on the awning of the shed;
and duckweed can be grown under the shed awning as pig feed.
Impact of Rice-Fish Culture
Production experience has demonstrated that fish farming in ditchpond makes good
use of the land, water, and biotic and abiotic resources of ricefields. The rate of
use and conversion efficiency of material and energy in the rice-fish ecosystem are
higher than in rice-only fields. The system is a desirable production model that
combines fish with rice.
Economic Benefits
Fish rearing in ditchponds has a low cost of investment but yields diverse products,
which in turn increase total agricultural income. This is demonstrated by some
examples from Shangyou County, Jiangxi Province.
In 1984, fish were raised in ditchponds on 86.5 ha of ricefields. The output of
fresh fish averaged 760.5 kg/ha, and the yield of rice increased by over
2 900 kg/ha. The value of the total output increased by CNY5 780/ha. Zhong
Linying, a farmer in Qixing, practiced monoculture of nile tilapia in a late ricefield
and produced 3200 kg of fish per hectare. Cai Yunging, in Henglin, adopted
150
RICE-FISH CULTURE IN CHINA
polyculture of grass carp, silver carp, bighead carp, and common carp and
produced an output of CNY15 860/ha (net income CNY14 700/ha).
In 1985-1987, experiments in various parts of Shangyou County produced positive
results. For example, a test of fish-rearing was undertaken by Kong Quingrong in
a 0.08-ha double-cropped ricefield (area of pond 0.01 ha). The rice harvest was
976.7 kg (9% more than from the same field planted to rice the previous year). In
addition, by using the field-bank ridge and shed awning to grow crops, he
produced 5 kg of soybean, 5 kg of balsam pears, 15 kg of tomatoes, 30 kg of white
gourds, 40 kg of musky pumpkins, 53 kg of kidney beans, and some other
vegetables and livestock feeds. The net income, including CNY264 from the fish,
was 3.6 times as much as in the previous year (an increase of CNY4 590/ha).
In 1986, this production system was extended in Dongshang Township. Results
from a 0.9-ha field distributed into 23 pieces of land were 40.2 kg (603 kg/ha) of
fish and a rice yield that averaged 11063 kg/ha (1.8% higher than in the previous
year). In addition, average income was CNY304/ha and total value reached
CNY5680/ha.
In 1987, results were obtained from five households in Dongshan Township. Kang
Renhai obtained 15 018 kg of rice, 975 kg of fresh fish per hectare, and CNY294
from other interplanted crops (e.g., taro, soybean, and pumpkin) for a total output
of CNY20400/ha. In contrast, an adjacent field that was the same size but had no
fish had an output that was 3.15 times lower in value.
Ecological Effects
The rice-fish system is an artificially controlled ecosystem in which rice and fish
coexist, depend on, and promote each other. Fish play several roles in the system.
Weed control and preservation of soil fertility. In the ricefield, weeds
compete with rice for nutrients, land, water, space, and sunlight. As a result they
greatly affect the growth of the rice plants. Experiments have shown that 1 kg of
grass-carp fingerlings in a ricefield consume about 40-60 kg of weeds, which
would absorb about 1.25 kg of nitrogen as they grow. In the rice-fish system,
weeds are eaten by grass-eating fish and their waste becomes a field manure that
helps conserve and enrich soil fertility.
Huang Xinlian, a farmer of Shuiyan Township in Shangyou County, adopted the
rice-fish system with a ditchpond for 3 years. In 1983, from a 0.06-ha field, she
obtained 1083 kg of grain (138 kg more than the previous year) and 38 kg of food
fish, 1109 large fingerlings of grass carp, silver carp, and common carp, and
32 Japanese crucian carp. She obtained a total income of CNY652 and a net
income of CNY451 (CNY7114/ha). In addition, she saved CNY12 for chemical
fertilizers and pesticides and no tillage or weeding were needed for 3 years. Soil
fertility and yields have increased each year.
PATTERNS AND TECHNOLOGY
151
Control of rice diseases and insect pests. Insects that are harmful to rice
are a good food for fish. For example, when they fall into the water, rice borers,
rice hoppers, and rice weevils are quickly eaten by the fish. Observations in
experiment plots have indicated that densities of pest populations were lower, as
was the damage to rice plants, when fish were present in the field. For example,
for the third and fourth generations of rice borer the density of the third generation
was 1305/ha and the rate of dead hearts in the rice was only 0.4% in the rice-fish
field. In the fourth generation, pest density was 1380/ha and the rate of white
heads was only 0.9% in the rice-fish field, but in a rice-only field the density was
1650/ha and the rate of white heads was 1.4%.
The vegetable and other crops grown on the field bunds also provide habitat for
natural predators. The crops on the bunds and shed awning also enhance fish
growth because they shade the water and lower water temperature.
The fish also reduces rice diseases by oxygenating the soil and speeding the
decomposition of manure and the release of available nutrients. Large grass carp
and common carp remove the basal leaves of the rice plant and diseased leaves,
which allows air and sunlight to pass through easily. This promotes rice growth
and reduces the incidence of rice diseases.
Early rice sheath-blight disease was investigated in Wangzai County. The incidence
of diseased hills was 17.1 % and rate of diseased plants was 2.7% in the rice-fish
field, compared with 42% diseased hills and a rate of 6.1 % for diseased plants in
the ricefield without fish.
Social Effects
Making multiple uses of the same field is an important advantage of this system.
Large fish fingerlings and commercial fish for market are produced without
additional land. For example, five farm households in Shanyou County produced,
from an area of 0.2 ha, an average yield of rice of 13 760 kg/ha, 568.5 kg/ha of
fish, and an income of CNY1310/ha from vegetables. Total income reached
CNY9635/ha.
Fish consume weeds and pests, prevent disease, conserve and increase fertilize,
reduce or eliminate chemical pesticides, and as a result, also save farm labour.
Experiments have demonstrated that 8-10 units of labour power are saved when
fish are present. The decrease in the amount of agricultural chemicals also reduces
chemical poisoning and environmental pollution. At the same time, natural pest
predators such as praying mantis, spiders, and frogs correspondingly increase. In
addition, because fish are predators of mosquito larvae and snails, they help
prevent malaria, flariasis, and snail fever.
Conclusion
Agricultural production is being changed in Shanyou County. Farmers now know
how to use the limited arable land for multiple purposes. There are several
152
RICE-FISH CULTURE IN CHINA
advantages to the new production system. First, the rice-fish system increases
economic benefits two or three times compared with a single rice crop. Second, the
production system integrates the main crop (rice) with fish and vegetables and
improves agricultural production. Third, the principles of a natural ecosystem are
borrowed to promote ecological balance and ecological cycles. Fourth, cropping
and fish-rearing are linked in a simple way that uses land, water, and biotic and
abiotic resources efficiently and features low inputs, quick effects, and excellent
benefits.
Because fish-rearing in the ditch pond of a ricefield is a new production system,
many items require further research. For example, the proportion of different
fishes and the proportion of pond and ditch area must be tested and studied. To
further improve the use of ricefield resources, cooperation is required between
scientists working in the departments of agriculture, protection, and health.
Rice-fish culture in the ditch ponds of ricefields has great potential. There are
1.3 million ha of ricefields that are suitable for fish-rearing in Jianxi Province. If
25% of these fields were used for rice-fish culture and the unit output of fish was
750 kg/ha, then 250000 tonnes of fish could be produced. This is 148000 tonnes
more than the total output of fish in 1984. At a market price of CNY3/kg, the
output of fish would increase income by CNY750 million. If CNY250 million were
produced from interplanted vegetables (CNY750/ha), the additional amount of
revenue would be CNY1000 million.
Techniques for Rice-Catfish Culture in Zero-Tillage
Ricefields
Chen Huarong.40
Yunnan is situated on a low-latitude plateau that has a variety of physical features
and many variations in climate. Agricultural production differs dramatically
between regions and seasons. Ricefields in Yunnan cover 1 million ha, and more
than 132000 ha are suitable for rice-fish cultivation. The rice-growing regions
vary from warm and sunny with plenty of rainfall and good soils to areas with low
temperature and poor water-holding capacity.
The ricefields are not efficiently used and economic returns could be improved.
Rice-fish fields only cover about 13 300 ha, which is only 10% of the area suitable
for rice-fish culture. Average output is also rather low (45 kg/ha in 1982, 62 kg/ha
in 1985, and 101 kg/ha in 1987) compared with the national average of 140 kg/ha.
Full exploitation of the potential productivity of the ricefields could remarkably
increase economic benefits. Rice-fish cultivation is an important way to increase
productivity. Experiments were conducted in Kunming, a rice-growing region of
Yunnan Province, at an elevation of 1900 m and with an annual average
temperature of 14.5° C.
Fish Species
The choice of species greatly affects fish harvests, the value of the output, and the
economic benefits gained from ricefields. The characteristics of the rice-growing
regions in the Yunnan plateau are low temperatures, low water temperatures,
shallowly flooded ricefields. The traditional fish species grow slowly and the
growing period is short. Given these conditions, it was important to find fish
species that grew quickly (reached market size in 120 days), tolerated low-oxygen
conditions, were of high quality, and produced high outputs. Experiments were
conducted in 1986-1988 to compare different species.
Vigour and Production
Different species were raised for 120 days in the ditches and beds of zero-tillage
ricefields. Growth rates and yields varied greatly (Table 1). Clarias leather grew
the fastest. Individual weights increased 168-fold and their average weights were
four times that of nile tilapia and 10 times that of the carp. The length of the cat-
40
Yunnan Academy of Agricultural Sciences, Kunming, Yunnan Province.
Table 1. Growth rate and yield of different fish species.
Lft
-U
Stocked Population*
Year
1986
1987
Pattern
Mixed"
Total
Wt.
(kg/ha)
Body
Length
(cm)
Body
Wt.
(g)
Harvest
(%)
Body
Length
(cm)
Body
Wt.
(g)
Length
Increase
(times)
Wt.
Increase
(times)
Output
(t/ha)
% of
total
output
C.
leather
7500
9.0
5.8
1.2
79.0
30.4
203.0
4.2
168.2
1.2
67.7
Nile
tilapia
7500
87.0
7.1
11.5
81.0
13.2
50.1
0.8
4.5
0.4
21.8
Carp
15000
9.0
3.3
0.6
61.8
10.0
20.1
2.0
32.5
0.2
10.5
Total
30000
105.0
—
—
70.9
—
—
—
1.8
100.0
C.
leather
12000
21.0
6.0
1.3
69.1
26.5
137.6
3.4
106.0
1.1
68.8
Carp+
crucian
carp
12000
276.0
10.0
23.0
55.1
15.0
78.2
0.5
2.5
0.5
31.2
Total
24000
297.0
—
—
62.1
—
—
—
1.6
100.0
Pure
C.
leather
15000
16.5
5.0
1.1
91.7
28.4
146.0
4.7
133.0
2.0
100.0
Pure'
(C. leather)
OYF
9000
531.0
17.5
59.0
99.0
32.5
217.1
0.9
3.8
1.9
63.0
YF
hatched
in 1988
12000
72.0
10.0
6.0
90.0
25.2
105.0
1.5
18.3
1.1
37.0
Total
21000
603.0
13.7
28.8
93.9
28.5
155.7
U
4.4
3.1
100.0
Mixed6
d
1988
Species
Fish
per ha
Harvest Characteristics
—
—
' Wt. weight; OYF overwintered young fish; YF young fish. b Fish cultured from 4 June to 5 October. ° Fish cultured from 29 May to 20 September. d C. leather
cultured from 27 May to 28 September; OYF from 29 April to 22 September. ' Fish cultured from 13 May to 22 September.
33
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Table 2. Economic benefits of different fish species stocked in ricefields.
Input (CNY/ha)
Year
1986
1987
Stocking
pattern
Mixed
Mixed
Pure
1988
Pure
(C. leather)
Output
Value
(%)
Input/
Benefit total input
ratio
(%)
Species'
C. leather
1050
555
1605
1.2
7245
73.5
5640
92.7
1:4.5
42.6
Niletilapia
600
555
1155
0.3
1522
15.5
367
6.0
1:1.3
30.7
Carp
450
555
1005
0.2
1080
11.0
75
1.3
1:1.1
26.7
Total
2100
1665
3765
1.7
9847
100
6082
100
1:2.6
C. leather
1680
525
2205
1.1
6849
68.8
4644
77.1
1:3.1
56.1
Carp+
Crucian carp
1200
525
1725
0.5
3105
31.2
1380
22.9
1:1.8
43.9
Total
Value
(CNY)
Net
income
(CNY/ha)
Young
fish
Feed
Output
(t/ha)
Economic benefits
%
100
TJ
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33
Total
2880
1050
3930
1.6
9954
100
6024
100
1:2.5
100
C. leather
2100
1950
4050
2.0
11898
100
7848
100
1:2.9
100
OYF
4140
2490
6630
2.0
17415
70.9
10785
71.8
1:2.6
69.5
YF hatched
in 1988
1950
960
2910
1.1
7137
29.1
4227
28.2
1:2.4
30.5
Total
6090
3450
9540
3.1
24552
15012
100
1:2.6
100
100
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156
RICE-FISH CULTURE IN CHINA
fish increased 4.2-fold. Yields of C. leather were the highest. When stocked at
25% of the population C. leather yielded 71.4% of the harvest.
Yields of C. leather were twice as high in monoculture than in polyculture (average
3.1 t/ha in 1988; largest individuals weighed 450-600 g). The size of the young
fish used for stocking influenced yield and economic return. Overwintered largesize young fish produced higher yields than smaller-size fish hatched the same
year. The survival rate of overwintered fish to food fish was 90%, and the harvest
increased significantly when larger-size young fish were used. Fish that were
15-20 cm in length constituted 63% of the average yield; whereas, fish less than
10 cm in length constituted 37% of the yield.
Economic Benefits
Economic benefits were closely related to the species (Table 2). C. leather
produced the best economic returns. In mixed culture, C. leather constituted 43%
of the total input and produced 74% of the total output value. Net income from
C. leather was CNY5 640/ha (93 % of total net income) and the benefit ratio was
1:4.5. The output value of nile tilapia and carp was 15-21 % of the total output, net
income was CNY75-367.5/ha, and the benefit ratio was between 1:1.1 and 1:1.3.
In monoculture, the output of C, leather amounted to CNY24 552/ha, net income
was CNY15000, and the benefit ratio was between 1:2.6 and 1:2.9
Experiments and demonstrations in ricefields over 3 years showed that C. leather
grows quickly, produces high yields, and is of good quality. C. leather is
considered to have 10 advantages. They grow exceptionally fast, individual fish are
large, they are omnivorous and capable of eating coarse food materials, they
tolerate "humble" living conditions, they are resistant to diseases, they have a high
survival rate, they tolerate of low oxygen levels, they are suitable for cultivation
in dense populations, they produce excellent output, and they produce good
economic benefits for farmers.
Rice-Fish Cultivation
The techniques for rice-fish cultivation have been improved. Different fish species
have been used and economic benefits have been increased by better integrating the
use of the ricefields. Two patterns of the cultivation are currently used.
Traditional Method
This is the main method used in Yunnan. Although the method does produce some
economic benefits, yields are limited because of deep ploughing, close planting of
the rice, the use of shallow-flooded fields with few ditches, the stocking of small
numbers of small fry, and no additional feeding and management. This pattern of
production yields on average less than 150 kg/ha (maximum 300-450 kg/ha). It is
important to improve the techniques and gradually encourage farmers to change
from low-yield, extensive cultivation to the high-yield, intensive methods of
cultivation.
PATTERNS AND TECHNOLOGY
157
Improved Method
This method combines the culture of fish in ditches and beds in the ricefield with
zero-tillage of the fields. This method has been successful in Kunming, a ricegrowing region with an annual average temperature of 14.5°C (monthly averages
from May to September are 18.9°C, 19.4°C, 19.7°C, 18.9°C, and 17.4°C).
Corresponding water temperatures in the ditches are 21.6°C, 22.1°C, 23.3°C,
22.2°C, and 20.3°C. Several steps are involved in establishing this type of
rice-fish system. First, choose a ricefield with good water supply and a convenient
irrigation and drainage system, good water-retaining properties, and little shade.
Second, dig ditches and divide the field into beds (zero-tillage) — ditches should
be 0.4-0.6 m in depth and 0.4-0.5 m in width, the beds 2-3 m wide, and the ditch
area should be 10-15% of the total area of the ricefield. Third, spread manure over
the field before the ditches are dug, pulverize and level the top soil, and dig out the
ditches to cover the manure before the rice seedlings are planted. Fourth, raise and
reinforce the surrounding small dikes with the subsoil dug from the ditches. The
ditches should be straight, level, and have a flat bottom. Tillage should not be
needed for 5 years.
The main features of this cropping pattern are: zero-tillage fields with deep ditches
and wide beds; rice planted in shallow water and rice and fish grown together;
symbiosis of rice and fish, which reduces stress on both; intensive management and
multiple use of water; and increased income from both rice and fish. Additional
ditches can be added without reducing yield, the ricefield can be dried without
damaging the fish, and chemicals can be applied to the rice without killing the fish.
Income generation. Rice-fish yields increased each year. Rice yields were
7-12% higher in the zero-tillage rice-fish system than in ploughed fields without
fish. Fish yields were more than 3 000 kg/ha, which was over 10 times the yield
of fish from ricefields cultivated in the traditional way. The value of rice plus fish
was CNY27525/ha and net income was CNY16815/ha (an increase of 8.6- to
19-fold, Table 3).
Ecological benefits. Increases in yields of rice and fish were closely related
to the patterns of zero-tillage, bed division in the ricefield, rice and fish being
grown together, and the selection of specific fish species. The rice and fish derived
mutual benefit from the system, and ecological conditions in the ricefield were
improved in several ways (Table 4).
•
Improved habitat. A mutually beneficially habitat was provided for
the rice and the fish. Circulation of air and penetration of light were
improved between beds and rows. Light penetration in fields with
bed divisions was 12.6% higher than in fields without divisions.
Water temperatures were 0.7°C higher, there were 6-10 more rice
grains per panicle, and the rate of empty, shrunken grains was
5-10% lower. These changes in light and water conditions favoured
growth of both fish and rice.
u»
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Table 3. Output and output value from different rice-fish cultivation patterns."
Input (CNY/ha)
Output Value (CNY/ha)
Rice+
Fish
Rice
Fish
6.5
1.7
2745
9864
Benefit
Ratio
1:2.6
12.1
Rice
Fish
1986
Rice + mixed
fish species
1425
3510
Control
1560
0
1560
5.8
0
2450
0
2450
890
1:1.6
0
Rice+pure
fish species
1425
3900
5325
7.1
2
2970
11898
14868
9543
1:2.8
10.3
Control
1725
0
1725
6.4
0
2692
0
2692
968
1:1.6
0
Rice+pure
fish species
1170
9540
10710
7
3.1
2973
24552
27525
16815
1:2.6
7.4
Control
1875
0
1875
6.5
0
2740
0
2740
866
1:1.5
0
1988
Fish
Net
Income
(CNY/ha)
Rice
Yield
Increase
(%)
Pattern
4935
Rice
3J
O
Economic Benefits
Year
1987
Total
Output (t/ha)
12609
7674
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* Values used in calculations were: CNY 3 for 1 labour-day input; CNY0.42 for 1 kg of rice output; CNY6 for 1 kg of fish output
(CNY8 in 1988).
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PATTERNS AND TECHNOLOGY
159
Table 4. Edge effect on rice in ditch-bed and zero-tillage rice-fish cultivation.*
Cult.b
80-2
Treat.
No.
ES
EB
No.
Full Grains Tillers/ Prod. Tillers
Grains Grains (%)
Plant Pan.c
(%)
Pan.
Wt.
(g)
Wt./
Row
(g)
Yield
(%)
Edge 1-3 121.6
96.2
21.0
1.67
376.5
52.0
2.50 2275
12.9
Control
115.4
83.6
27.5
1.60
330.0
45.5
2.17 2015
0
79-635 Edge 1-3 84.8
70.4
17.0
2.24
684.0
60.5
1.542125
19.0
Control
54.0
27.2
2.11
618.0
56.3
1.24 1900
0
74.3
"Plant population: single-row strip, 3 x 5 , 600000 stands per hectare; Control: edge 6 rows;
weight per row: total weight of 108 stands in a row.
b
Cult, cultivar; Treat. Treatment; ES empty-shrunken; pan. panicle; EB ear-bearing; Pan. wt.
Panicle weight; Wt./row Weight per row.
c
Values in this column are x 10 000.
•
•
Higher yields of rice. Experiments have shown that in zero-tillage
fields, shallow-planted plants constitute 94.6% of the population. In
ploughed fields, deep-planted plants make up 77.2% of the
population. (Shallow-planting less than 6.7 cm, deep planting more
than 10 cm). Shallow-planted plants recover more readily, tiller
earlier, and more vigorous, have a larger number of productive
tillers, a higher percentage of ear-bearing tillers, a lower percentage
of empty, shrunken grains, and have heavier panicles with less
diseases (Table 5). Zero-tillage is a new practice that solves the
problem of plants being planted too deep and also saves energy and
labour.
Improved soil fertility. Rice-fish culture is an efficient way to
accelerate soil enrichment. Ricefields provide fish with a rich source
of natural food, and the fish excrete manure, loosen the soil, and
eradicate weeds. Soil analysis (Table 6) shows that rice-fish
cultivation with successive zero-tillage increased organic matter and
active nitrogen, but reduced phosphorus in the soil. It is necessary
to apply large amounts of manure and smaller amounts of
fertilizers. With successive rice-fish cultivation, it is particularly
important to control nitrogen and increase phosphorus to maintain
steady rice growth during the entire crop cycle.
Because the fish loosen the soil, the soil has higher permeability,
which promotes decomposition of complex soil nutrients, manure,
and fertilizer and improves rice growth. Root systems are also
better developed (25.5% increase) and more widely and deeply
distributed. Large amounts of weeds were eaten by C. leather,
which has a good appetite and also devours insects. As a result, the
ricefields were nearly free of weeds without cultivation or weeding.
8
Table 5. Effects of ditch-beds, zero-tillage rice-fish culture, and ploughing on planting depth of rice seedlings.
Less than
6.7 cm
Cult.'
Dianyu
No.l
80-2
1
6.7 cm
More than
10 cm
i
31
c/>
I
No.
Grains
Full
Grains
(%)
ES
Grains
(%)
Prod.
Ears"
EB
Tillers
%
Pan.
Wt.
(g)
Dis.
Plants
(%)
0
87.2
70.4
19.3
529.5
75.4
1.4
20.8
5
12.2
77.2
43.3
87.8
61.0
30.5
480.0
60.8
1.3
34.7
5.8
0
34.8
5.4
8.7
112.0
91.8
18.0
313.5
78.6
2.7
18.2
8.4
12.1
49.0
76.2
18.3
108.5
84.2
22.4
313.5
70.1
2.4
25.6
7.7
0
Till.
Pat.
Sc
(%)
T
(%)
S
(%)
T
(%)
Plow
29.0
30.4
71.0
Zerotillage
4.7
7.1
Plow
30.8
Zerotillage
9.5
S
(%)
T
(%)
69.9
0
18.1
49.6
56.5
63.8
32.7
14.3
O
Yield
(t/ha)
Yield
(%)
c
c
3}
m
Z
O
I
Cult, cultivar; Till. Pat. Tillage pattern; ES Empty-shrunken; Prod, productive; EB ear-bearing; Pan. Wt. panicle weight; Dis. diseased.
Values in this column x 10 000.
c
Planting depth sampled at tillering peak (on 30 June). S = seedlings; T = tillers.
b
3
o
m
Z
>
PATTERNS AND TECHNOLOGY
161
Table 6. Soil nutrients in experimental rice-fish cultivation fields
(zero-tillage practiced in successive years).
Organic
Matter
Active Active Active Total
N
P
K
N
(ppm) (ppm) (ppm) (%)
Total
P
(%)
Total
K
(%)
Year Treatment
pH
1984
Control
(before fish
stocking)
6.73
4.101
161.2
94.50
61.69
0.208
0.160
2.055
1985
1st year of
rice-fish
cultivation
6.38
4.848
167.3
74.10
-
0.228
0.111
2.454
1986
2nd year of
rice-fish
cultivation
6.41
5.014
233.8
12.18 172.19 0.231
0.110
2.659
1987
3rd year of
rice-fish
cultivation
6.24
5.269
-
10.46
0.122
2.643
84.9
0.245
In contrast, fields planted to rice, but not stocked with fish, require
weeding twice during the growing season and still contained
2 000 kg of weeds per hectare at harvest. Oriental army worms and
rice planthoppers were eaten by the fish; therefore, no pesticides
were needed and labour for spraying was saved. The percentage of
diseased rice plants decreased by 7-14% compared with fields
without fish.
Conclusion
The most desirable fish species for rice-fish cultivation in the Yunnan plateau is
C. leather. It grows quickly, is of good quality, tolerates low oxygen, and can be
stocked at high densities. The use of ditches and beds, combined with zero-tillage,
produced the best economic returns from rice-fish cultivation in Yunnan. This
system produces increased outputs and income from both rice and fish and imparts
additional ecological benefits to the ricefield.
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Demonstration of High-Yield Fish Farming in Ricefields
Cat Guanghui,41 Ying Yuguang,42 Wu Baogan43 He Zhangxiong,44 and
Lai Shengyong45
Traditional fish farming in ricefields yields about 150 kg of fish per hectare. To
improve economic efficiency and stimulate the development of a commodity
economy in rural areas, improvements have been made in rice-fish culture since
1984 in several major rice producing provinces (e.g., Sichuan, Hunan, Hubei,
Jiangxi, Guangxi, Anhui, Jiangsu, Zhejaing, Guizhow, Guangdong, and Yunnan).
In 1986, the Science and Technology Commission of Guangxi Autonomous Region
assigned a rice-fish project through the Spark Program to the Guangxi General
Station of Aquatic Technical Extension. Demonstration experiments were
conducted in ricefields for 2 years. High yields of rice and fish were obtained over
large areas using a ditch and pit method. In 1986, the experimental area amounted
to 48 ha and 29 657 kg of fish were harvested. The average yield was 620 kg/ha
which was 3.8 times the average yield of other rice-fish systems in the region. The
average rice yield was 10700 kg/ha. In 1987, the demonstration area was increased
to 55.5 ha, the total fish yield was 40268 kg (average 725 kg/ha), and the average
rice yield was 11610 kg/ha. These results surpassed the target of the specialized
contract by 525-600 kg/ha of fish and more than 7 500 kg/ha of rice.
Experimental Methods
Experimental Fields
The two methods that were used were the pit and ditch method and the ridge and
ditch method.
41
Guangxi General Station for Extension of Aquatic Technology, Nanning,
Guangxi Autonomous Region.
42
Livestock and Aquatic Bureau of Yulin Prefecture, Yulin, Guangxi
Autonomous Region.
43
Aquatic Technology Extension Station, Guilin Prefecture, Guilin, Guangxi
Autonomous Region.
44
Aquatic Technology Extension Station, Wuzhow Prefecture, Wuzhow,
Guangxi Autonomous Region.
45
Agriculture, Animal Husbandry, and Fishery Bureau, Quanzhou
Prefecture, Quanzhou Autonomous Region.
164
RICE-FISH CULTURE IN CHINA
Pit and ditch method. In 1986, there were 48 ha of demonstration fields
and 529 households participated. In 1987, there were 55.5 ha of fields and
658 households. The experimental fields were distributed from north to south in
a total of 26 towns in 14 counties.
Water resources in the experimental fields were abundant, drainage and irrigation
were convenient, and yields were ensured despite drought or flood. Before the
early rice was transplanted, 6-8% of the ricefields were dug into fish pits that were
65-100 cm deep. At the same time, the footpaths between ricefields were dug
20 cm deeper to form fish ditches that connected all of the fish pits.
Ridge and ditch method. In 1987, in Cenqui County of Wuzhow District,
experiments were conducted using a ridge and ditch method on 3.4 ha. Seven days
before the early rice was transplanted, the ricefields were tilled and base manure
was spread. All of the water was then drained from the field. A ditch (50 cm wide
and 40 cm deep) was then dug around the field. If the field was large area, an x- or
#-shaped ditch was dug. After the ditch was dug, the ridges were made in an
East-West direction. The ridges were 24-26 cm wide and 20-22 cm high. The
ditches were 36-40 cm wide and 20-22 cm deep.
Stocking Methods
Two methods of stocking were used: single stocking and two stockings. Single
stocking is usually done before the end of April. When two stockings are used, the
first is between early April and early May when the early rice is transplanted. The
second stocking occurs during the second half of July. Larger fish are partly
harvested before or after the harvest of the early rice, and fish fry (4-7 cm long)
are stocked.
In 1987, fish fry were stocked at the rate of 11985 fry/ha. The fish stocked were
80% common carp, 6.1% grass carp, 11% nile tilapia, 2% silver carp, and 0.6%
bighead carp. Various experiments were conducted to investigate the effects of:
stocking carp at different densities, different species (common carp, grass carp, and
nile tilapia), and different feeds (fresh plants, concentrates, and fresh plants mixed
with concentrates). Additional comparisons were made between rice yields with
and without fish in one ricefield divided into two parts. These experiments were
carried out at all the 14 counties.
Day-to-Day Management
Rice production in the demonstrations field was conducted according to the
conventional methods used by farm households. In most demonstration fields no
weeding was done. The depth of water in the ricefields was generally between
6 and 10 cm; however, during the flowering period the water depth was increased
to 15 cm. Atmospheric temperature varied between 16.5°C and 39°C, water
temperature was 20-36.5°C, and pH was 6.4-7. Bran cake, green forage, and
fertilizer was applied as required.
PATTERNS AND TECHNOLOGY
165
Collection of Data
In each of the 14 districts, one observation station was established for every 3.3 ha
of ricefields and 37 farm households were used for observation. Aquatic scientists
and technicians visited the experimental fields periodically to make observations
and record data.
Results
Yield of Fish and Rice
Fish and rice were grown in the experimental fields for between 176 and 320 days.
In 1986, the 48 ha of ricefields yielded an average 620 kg of fish per hectare. This
represented an increase of 4.8 times the average yield of 106 kg/ha obtained from
rice-fish culture in the district. The average rice yield with fish was 10 700 kg/ha,
an increase of 4.8% compared with ricefields without fish at the same location.
In 1987, there were 55.5 ha of demonstration fields. The average fish yield was
725 kg/ha, which was an increase of 5.5 times compared with the average yield in
the district. The average rice yield with fish was 11605 kg/ha, an increase of 7.2%
compared with fields without fish. There were 3.4 ha of rice-fish in the ridge and
ditch method. The average rice yield was 12307 kg/ha, an increase of 8.9%
compared with other ricefields.
Survival Rate and Average Weight
In 1987, 665711 fish were stocked in the demonstration fields and 439557 fish
were harvested. The average survival rate was 66%. Survival rates for each species
were: carp 65% (52-79%); grass carp 67% (52-75%); nile tilapia 65% (50-78%);
silver carp 68% (62-76%); and bighead carp 75% (71-77%).
The average weights of the different fish varieties were: carp 69.6 g; grass carp
242.6 g (the largest fish was 400 g); nile tilapia 116.1 g; silver carp 255.3 g; and
bighead carp 343 g. The yield proportion of the different species was: carp 60%,
grass carp 16%, nile tilapia 14%, silver carp 6%, bighead carp 3%, and others
1.1%.
Stocking Densities
In 1987, at Guangyang County, Guilin District 3, 0.16 ha were used for trials of
different stocking densities (4500, 9000, and 15000 fish/ha). Stocking at a density
of 9000 carp fry per hectare produced the highest yield (834 kg/ha). At a density
of 4 500 carp fry per hectare yield was 495 kg/ha. At 4 500 carp fry per hectare,
the average weight per fish was highest. The largest fish was 73.1 g. At a density
of 9000 fish per hectare, the largest fish was 70.8 g; at 15 000 fish per hectare the
largest fish was only 37.9 g.
166
RICE-FISH CULTURE IN CHINA
Varieties
In 1986, trials were conducted with crucian carp, grass carp, and nile tilapia as the
main stocked fish. High yields could be obtained for all species. When summer
grass carp were stocked at 27 000 fish per hectare, with the objective of rearing
large fingerlings, 14400 fry larger than 10 cm were harvested per hectare (survival
rate 53%).
Feeding
In 1986, trials of different fish feeds were undertaken. No matter what kind of feed
was used (e.g., farmyard manure, green fodder, bran cakes, or combinations of all
three), the yield of fish could be increase. A combination of concentrated feed,
green fodder, and farmyard manure produced the highest yields.
Rice-fish Compared with No Fish
In 1987, in a total of 1.7 ha of ricefields owned by 22 households in four districts,
experiments were conducted to compare rice-fish farming with rice-only farming.
The heading rate, fruiting rate, number of grain per head, 1000-grain weight, and
nitrogen, phosphorus, and potassium levels in the soil were higher in the rice—fish
systems. The average yield from the rice-fish fields was 5.6% higher (Tables 1
and 2).
Economic Efficiency
The direct economic gain from the experimental fields during the 2-year period was
increased to CNY222 840 . Of this amount, CNY181902 was net income derived
from fish farming. The demonstration experiments on 1070 ha of ricefields
produced an average fish yield of 293 kg/ha and net income was increased to
CNY11 530/ha. The total benefit (direct plus indirect benefits) was over CNY1
million. The ratio between input and output was 1:5.51.
Ecological Effects
Fish grown in the ricefield eat mosquitoes and control diseases. Research
conducted in 1987 in Quanzhou County by the Parasitic Disease Research Institute
of Guanxi Autonomous Region, and the Sanitation and Antiepidemic Station of
Quanzhou County. Carp and grass carp raised in ricefields successfully controlled
mosquitoes. The relative density index (RDI) was between 0.9 and 42.9. In
general, the number of larva and pupa in rice-fish fields was remarkably lower
than in the fields without fish.
Conclusion
Several new techniques have been introduced to help improve traditional rice-fish
culture:
PATTERNS AND TECHNOLOGY
167
Table 1. Rice yields with and without fish culture in four districts (1987).
1000-Grain
Weight (g)
Full Grains
(%)
Grains/Head
Yield
(kg/ha)
District
Rice
RP
Cont.
RF
Cont.
RF
Cont.
RF
Guilin(O.lha)
(1 household)"
early
28.3
27.8
86.4
82.3
126.0
117.0
7632
6135
late
27.0
26.9
82.1
78.4
118.0
105.0
6750
6225
Wuzhou (0.3 ha) late
(2 households)
25.3
24.8
80.2
78.8
127.7
109.6
6606
6206
early
25.6
24.8
89.0
87.5
124.3
118.4
11654
11037
late
24.8
24.1
86.9
81.9
-
-
-
-
26.6
25.3
83.0
72.2
125.4
121.1
Yulin(0.6ha)
(9 households)
Qinzhou(1.7ha)
(10 households)
Cont.
5537
4857
*RF rice-fish culture; Cont. no fish culture.
b
Weeds were reduced by 430 kg/ha in rice-fish fields in Yulin District; 3117 kg/ha in
Qinzhou District. Weeds in rice-fish fields in Guilin District were 7.7% of the level in the
control field.
Table 2. Weed and insect infestation and soil fertility of ricefields with and without fish
culture.
Weeds
Insects
(g/m2)
(no./m2)
Soil Fertility (%)
RF
District
Rice RF* Cont.
Guilin (0.1 h a )
(1 household)
-
Wuzhou (0.3 ha) (2 households)
Yulin (0.6 ha)
(9 households)
RF
Cont.
N
P
K
N
P
K
1 . 5 19.5
_
_
_
_
_
_
_
_
2.8 3.6
-
-
0.19 0.06
1.22
0.19
0.06 1.27
early 79.0 103.6
0.67
4.97
late
67.9 111.0
0.81
2.11
31.0 343.0
0.51
0.60
Qinzhou (1.7 ha) (10 households)
Cont.
* RF rice-fish culture; Cont. no fish culture.
-
-
-
-
-
-
0.16 0.09
1.06
0.14
0.08 1.03
0.18 0.12
0.44
0.16
0.03 0.40
168
RICE-FISH CULTURE IN CHINA
•
•
•
•
•
•
Pit, ditch, and ridge and ditch fish-farming systems in ricefields are
modifications of traditional methods. The objective of these new
methods is to reduce conflicts between fish farming and rice
growing and to increase the yields of both rice and fish and raise the
economic efficiency of the ricefields.
Carp, grass carp, nile tilapia, silver carp, and chub are now mixed
for rearing. The traditional method of raising only carp was
changed to increase fish yields, promote rice production, and
improve sanitary conditions in the rural areas.
The use of over-wintered fmgerlings has significantly increased fish
output compared with the traditional method of breeding fingerlings
the same year.
The combination of the production of edible fish with the culture of
fingerlings has changed the habit of breeding only fingerlings or
only edible fish. This has provided edible fish and abundant fish
varieties for market.
The introduction of appropriate feeding has promoted fish growth
and increased income.
One species of fish adapted to local conditions is now used as the
major species. Selection of brood stock has also been improved.
The key techniques used to increase fish yields in ricefields are:
•
•
•
•
Use reasonable stocking densities and ratios of multiple fish
varieties. Grass carp, nile tilapia, silver carp, and variegated carp
were stocked at a rate of about 12 000 fish/ha.
Breed and stock over-wintered fingerlings.
Dig fish pits and fish ditches to solve the contradictions between
fish farming and rice management.
Apply appropriate fertilizers and feeds to supplement natural feeds
found in the ricefields.
Rice-Azolla-Fish in Ricefields
Chen Defu, Ying Hanquing, and Shui Maoxing46
The yield per hectare of traditional fish-raising methods is only 75-150 kg in
China. In Zhejiang Province, a high-yield rice-azolla-fish system was developed
and extended to farmers. The technique has now been adopted in many regions in
Zhejiang Province, and rice production and fish yields have both increased. In
1987, a demonstrative farmer, Shao Shousheng in Yuhang County, tested the high
yield rice-azolla-fish system. The Zhejiang Academy of Agricultural Sciences,
Yuhang Agricultural Committee, and Yuhang Science and Technology Society
conducted the experiments. The techniques used to simultaneously raise rice,
azolla, and fish are discussed.
Test Methods
The test field was located in Xingqiao Village, Yuhang County, 2 km from
Hangzhou City. The field was 0.3 ha and had been used in 1986 as a test field for
high-yield fish culture. Therefore, the farmer, Shao Shousheng, had practical
experience. The fish ditch was 3 m in width, 1 m in depth, and occupied 21% of
the total ricefield. Fine feed was used as the main fish food, and organic manure
and fertilizers were used as supplements. Omnivorous, carp and crucian carp were
raised. In 1986, the yield of rice was 9 730 kg/ha and the net yield of adult fish
was 3 426 kg/ha. A comprehensive experiment on rice-azolla-fish was started in
1987 and several changes were made in rearing techniques:
•
•
•
Instead of using fine feed for the fish, the fine feed was first fed to
pigs and the pig manure was fed to the fish.
Rice-azolla-fish were grown together in 1987, and the azolla were
used as the main feed for the herbivorous fishes.
Herbivorous fishes were chiefly raised in 1987 (silver carps,
common carp, and crucian carp).
Test Results
Yield of Rice and Fish
The rice yield was 9786 kg/ha in 1986. The early japonica rice (Biyuzaonuo) grew
well in 1987 and produced an additional 980 kg/ha. However, transplanting of the
late rice was delayed to nearly the beginning of Autumn because the early rice was
46
Zhejiang Academy of Agricultural Sciences, Hangzhou, Zhejiong
Province.
170
RICE-FISH CULTURE IN CHINA
late to mature. It was also difficult to keep the grass carp in the fish ditches away
from the rice on the sides of the ditches. Because the fish eat some of the rice, rice
yield decreased to 1233 kg/ha, but the yield of adult fish increased greatly
(Table 1). In 1987, the yield of adult fish from the rice-azolla-fish system was
6 990 kg/ha, an increase of 71 % over the 4 200 kg/ha in the rice-fish system in
1986. If the yield of fish fry is excluded, the net yield of adult fish was 5 500 kg
in the rice-azolla-fish system, an increase of 60% over the 3444 kg/ha in the
rice-fish system.
Feed Consumption and Cost
Fine feed was the main food source for the fish in 1986, and 7 300 kg/ha of feed
were consumed. Therefore, the cost of fish raising was rather high. Major
modifications were made in 1987. The fine feed was first used to feed pigs. The
pig manure was then fed to the fish and used to fertilize the azolla. This
modification made full use of material inputs and added four pigs to the output
with limited input. The cost of feed for fish raising was also reduced. The unit cost
of feed in the rice-azolla-fish system was only 47% of the cost in the rice-fish
system, and the feed cost of fish per kilogram was 29% of the cost in 1986
(Table 2).
Economic Efficiency
The cost of fish raising was almost equal both years. The output value and net
profit in the rice-azolla-fish field increased significantly because the adult fish
yield in the rice-azolla-fish field was higher than that in the rice-fish field. The
output value was CNY17100/ha and net profit was CNY9 278/ha in the rice-fish
field in 1986; whereas, in 1987, the output value was CNY25 404/ha and the net
profit was CNY17528/ha in the rice-azolla-fish field (an increase of 89%,
Table 3).
Analysis and Discussion
There were several reasons for the yield increase and the cost decrease in the
rice-azolla-fish fields.
Use of Herbivorous Fishes
Herbivorous fishes (grass carp and bream), especially grass carp, are fond of azolla
and grow quickly. When there is a sufficient supply of azolla there is great
potential for yield increase. The omnivorous fishes (carp and crucian carp) require
high-quality fine feed, but grow slowly. These omnivorous fishes were the most
numerous in 1986 (79% of the fish and 72% of the total weight). Herbivorous
fishes comprised 14% of the fish and 15% of the total weight. Among the
herbivorous fishes, grass carps accounted for 5% of the fish and 4% of the weight.
In 1987, azolla was grown in the ricefields and herbivorous fish were the main
species raised (48% of the fish and 31 % of the weight). Grass carp accounted for
PATTERNS AND TECHNOLOGY
171
Table 1. Yields of rice and fish in rice-azolla-fish and rice-fish systems.
Early Rice Late Rice
Yield
Yield
(kg/ha)
(kg/ha)
Annual
Yield
(kg/ha)
Fish
Yield
(kg/ha)
Fingerling Adult Fish
Yield
Yield
(kg/ha)
(kg/ha)
Rice-fish
4208
5579
9786
4119
678
3443
Rice-azolla-fish
5190
4347
9537
7038
1535
5499
Table 2. Fine feed consumption and cost of rice-azolla-fish and rice-fish systems.
Fine
Beer
Pig
Cost/kg
Feed Leftovers Manure Fertilizer Azolla
Cost
of Fish
(kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (CNY/ha) (CNY)
Rice-fish
7301
-
11243
543
Rice-azolla-fish
1023
575
34110
506
—
2471
3206
0.93
1494
0.27
Table 3. Economic efficiency of rice-azolla-fish and rice-fish systems.
Rice-Fish
(CNY/ha)
Output value
Cost
ProHt
Rice-Azolla-Fish
(CNY/ha)
Rice
3579
3503
Fish
13515
21902
Total
17094
25397
Rice
414
414
Fish
7402
7468
Total
7816
7882
Rice
3165
3089
Fish
6113
14434
Total
9278
17522
32% of the herbivorous fish and 29% of the weight, and bream 16% of the fish
and 1% of the weight. Omnivorous fishes comprised 7% of the fish and 11% of
the weight. Oligophagous fish (silver carp) accounted for 45% of the fish and 58%
of the weight (Table 4). The azolla were consumed by the herbivorous fish, and
the manure from the grass carp increased the amount of plankton, which raised the
yield of silver carp.
172
RICE-FISH CULTURE IN CHINA
Proportions and Harvest of Fish
In 1986, too few fish were raised early in the year and too many were raised later.
At high densities, all fish were almost the same size, which made batch harvesting
impossible. The market size of the fish harvested at the end of a year was also low.
In 1987, the density of the fish was reduced in rice-azolla-fish system. In addition,
983 larger fish (3760/ha) were stocked, which accounted for 27% of the total
number of fish raised (1123 kg). Of these larger fish, 188 were the grass carp
(719/ha), 300 were the common carp (1148/ha), and 495 were silver carp
(1757/ha), with the mean weight of 0.42 kg, 0.15 kg, and 0.38 kg, respectively
(Table 5). In this way, the fish-holding capacity early in the year increased to
102 kg in 1987 from 45 kg in 1986. Grass carp and common carp fed on azolla in
mid-March; whereas, the larger grass carp fed heavily on azolla during April to
June. Grass carp and silver carp were caught in batches to supply the market.
During April to October, 851 kg of large fish were harvested.
Azolla
The growth of fish and azolla in rice-azolla-fish system were different. Azolla
grows quickly in the spring when the fish are small, grow slowly, and eat little. At
this time, the azolla supply exceeds demand. In July and August, azolla grows
slowly and the fish grow quickly; therefore, the demand for azolla exceeds supply.
Three methods were used to mitigate this problem.
Harvest adult fish. At the end of June, adult fish were caught for market
to decrease the fish-holding capacity of the field when the azolla were growing
slowly. The grass carp grow very quickly during September, which is the second
peak of azolla growth.
Supplement supply of azolla. The azolla supply in rice-azolla-fish fields
could not satisfy the demand during July to August. Azolla from nearby ricefields,
ditches, and ponds were used to supplement the supply. Green-stored azolla and
dried azolla were also used.
Adjust feed. Less fine feed was used when azolla were plentiful, and more
fine feed or grass was fed when azolla levels were insufficient.
Stopping Fish From Eating Rice
Two methods were used to stop the fish from eating the rice. The fish were kept
in the fish pits with dikes and nets after the rice was transplanted. In addition, a
grass field and feed platform were established in the fish pit for the omnivorous
fish. Tender grass was placed in the grass field. Fine feed was placed on the feed
platform when the tender grass was almost completely eaten.
173
PATTERNS AND TECHNOLOGY
Table 4. Effects of use of different fish on yields from rice-azolla-fish
and rice-fish systems.
Rice-Fish
Fish Raised
per ha
(kg)
(No.)
Rice-Azolla-Fish
Fish Breed
Ratio (%)
(No.) (Wt.)
Fish Raised
per ha
(No.)
Fish Breed
Ratio (%)
(kg)
(No.)
(Wt.)
Herbivorous fish
Grass carp
1339
28.7
4.6
4.2
5096
458.1
32.9
29.8
Bream
2559
74.6
8.8
11.0
2349
14.7
15.2
1.0
Total
2398
103.2
13.3
15.2
7444
472.8
48.1
30.8
13711 281.3
46.8
41.6
1148
172.2
7.4
11.2
—
—
—
Omnivorous fish
Commoncarp
Crucian carp
Total
9564
204.6
32.6
30.2
-
23274
485.9
79.4
71.8
1148
172.2
7.4
11.2
2127
5.9
7.3
13.0
6905
890.4
44.6
58.0
30491
677.1
100
100
15497 1535.1
100
100
OHgophagous fish
Silver carp
Total
Table 5. The proportion of species and larger fish in rice-azolla-fish
and rice-fish systems (0.26-ha ricefield).
Rice-Fish
Rice-Azolla-Fish
Old
Size
(g/fish)
No.
Fish
Size
(g/fish)
417.5
Winter Fish
No.
Fish
188
Size
(g/fish)
No.
Fish
36.1
1144
Proportion of
Larger Fish
(%)
Grass carp
21.4
350
Bream
29.2
669 -
Commoncarp
24.9
1684
150.0
300
—
—
7.4
16.6
1900
-
-
-
-
-
Crucian carp
21.4
2500
—
—
—
—
—
Silver carp
41.1
556
375.6
495
42.6
1310
12.2
Total
23.1
7659
305.7
983
32.9
3068
24.3
-
6.3 614
4.6
-
174
RICE-FISH CULTURE IN CHINA
Raising Fish in Flowing Water
Flowing water has a high oxygen content, which favours fish growth. New
irrigation water was added at regular intervals. During cloudy, muggy weather,
when the fish lacked oxygen, a submersible pump was used to make the water flow
and increase the oxygen content. Once a month, 75 kg/ha of quick lime were
diluted in water and sprayed over the field to decrease the concentration of acid in
the water. This treatment promotes the breakdown of organic materials and helps
sterilize the water and prevent fish diseases.
Pig-Azolla-Fish-Rice System
This system reduced the cost of raising fish. Pigs were fed with fine feed. Fish and
azolla were fed with pig manure. Azolla were used to feed the pigs. Fish manure
also enriched the field. In this way, costs were reduced while net profit was
increased.
Conclusion
Experiments in 1987 indicated that the high-yield rice-azolla-fish system was a
success. Fish yields and net profit were increased and rice yields were maintained.
This system can improve the economic efficiency of the ricefield; nevertheless,
there are still some problems that require further study.
•
•
•
•
•
Grass carp quickly grow to a large size. Silver carps are smaller and
have a lower commercial value. The appropriate proportion of
silver carp to grass carp must be studied. Bream grow slowly and
should be raised in small proportions in rice-fish-azolla fields.
In 1987, dikes and fish nets were used to prevent the fish from
eating rice. This was expensive in both capital and labour. Many
late rice seedlings were eaten by the fish in 1987, which resulted in
a decrease in rice yield. Changes to the design of the fish ditch are
proposed to allow the farmers to block the fish with one dike and
one net. This would make the operation easier and more convenient.
Azolla continue to grow in the winter and spring. This potential
should be developed to build up resources that can be used as fish
feed.
The rice yield might be improved by transplanting the rice seedlings
earlier. In 1987, rice seedlings were transplanted during the second
10 days of May. This caused the ripening stage to be postponed.
The rice yield might be increased if seedlings were transplanted
during the first 10 days of May.
The harvesting method for the fish should be changed. Fish should
be raised and harvested on a rotational basis. This means that
different species should be raised in different proportions. The
appropriate size and time of harvest also needs to be established for
each species.
Part III:
Interactions
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Material Cycles and Economic Returns in a Rice-Fish
Ecosystem
M Dashu and Wang Jianguo47
In the rice-fish ecosystem materials move in a benign cycle and the energy flows
in the direction favourable to both rice and fish. The ricefields nourish the fish, and
the fish nourish the rice. Like other theories, the theory of rice-fish mutualism has
only been adopted slowly. The meaning of the word mutualism has, in recently
years, been extended from its original meaning in classical ecology. It has now
taken on the meaning of functional mutualism in addition to the original
organization sense. A mutual relationship is one in which two different species live
together and promote and accelerate their growth.
Although rice and fish are mutually beneficial, they are not totally dependent on
each other. Their coming together is based on scientific principles and the
anticipation of greater economic returns. As the system is further developed, and
rice-fish culture is widely recognized as the best way to increase yields, their
mutualism will become more of a necessity.
Chinese ecologist Ma Shijun said it is necessary to simulate mutualism of different
species of plants and animals according to one's needs. The theory of rice-fish
mutualism was founded on both conceptional and practical principles.
Rice-Fish Ecosystem
Ecology, in a direct sense, is a branch of science that studies habitat. It is, indeed,
very closely related with the development of the national economy. In nature,
animals, plants, and microorganisms come together to form a unified entity, or
ecological system. The close relationship among animals, plants, and
microorganisms and between these organisms and the environment, is made
possible by the flow of energy and the circulation of material.
Ecological systems are both large and small. The biosphere is a large system; a
ricefield or pond is a small ecosystem. In addition to these natural ecological
systems, there are other ecological systems, such as the rice-fish system. All
agricultural systems are, in fact, anthropogenic.
The nonbiological factors in the rice-fish ecosystem include light, water, water
temperature, pH, carbon dioxide, oxygen, and some inorganic matter. The
biological factors in the ecosystem include producers, consumers, and
47
Institute of Hydrobiology, Academia Sinica, Wuhan, Hubei Province.
178
RICE-FISH CULTURE IN CHINA
decomposers. The main producers are plants with roots and large and small
phytoplankton. In another words, there are three categories of producers in
ricefields: rice plants, weeds, and algae. They are all involved in the circulation
of carbon through photosynthesis and respiration, and they provide organic matter
to consumers and decomposers.
There are also many consumers. They include zooplankton (protozoa, rotifers, and
crustaceans); benthos (nematodes, molluscs, annelids, and water insects); fish
reared in ricefields (common carp, crucian carp, bighead carp, nile tilapia, and
grass carp); mosquito larvae, insects, and worms harmful to rice; natural enemies
of harmful insects and worms (spiders and parasitic wasps); and the natural
enemies of fry (chilopods, scorpions, dragonflies, frogs, otters, water rats, eels,
loach, water snakes, sandpipers, ducks, kingfishers, gulls, and egrets). Many
animals are both primary consumers and secondary or tertiary consumers. For
example, water snakes feeds on frog, frogs feed on fry, and fish feed on plankton.
Many animals are harmful to rice but useful to fish, and vice versa. For example,
although frogs feed on fry, they also feed on many of other insect and worms that
are harmful to rice. The composition of the producers, consumers, and
decomposers in the rice-fish ecosystem is complicated and merits further
investigation.
Cycling of Material and Energy Exchange
To create a rice-fish ecosystem in a ricefield, it is necessary to pay attention to the
appropriate time and size of the system to ensure that the rice and fish are truly
mutually beneficial. Material must be made to circulate in a benign cycle and the
energy flow must be in a direction favourable to both rice and fish (Figure 1). The
rice-fish ecosystem is created by adding fish fry or fingerlings to the ricefield. In
this system, the cycling of matter and the movement and storage of energy
becomes more rational. The difference, compared with a natural ecosystem, is that
the rice-fish system is controlled and adjusted by the farmer. Of course, to perfect
such an ecological system, many improvements are needed.
In the rice-fish ecosystem, rice is the dominant biological community. It absorbs
large quantities of light, carbon dioxide, water, and inorganic elements and
manufactures organic matter by photosynthesis. The large quantities of weeds,
plankton, and photosynthetic bacteria in the ricefield undertake the same processes.
However, they do not provide useful products. On the contrary, they compete for
fertilizer, space, area, and sunshine with the rice and in some cases are the
intermediate hosts of rice pests. Of course, weeds and plankton are all primary
producers that help fix and store energy. The primary consumers are mainly
zooplankton, herbivorous animals, and plant pests. The secondary consumers are
mainly carnivorous animals.
Fish in the rice-fish system can be primary consumers, secondary consumers, or
tertiary consumers. This creates the problem of which fish to raise to make the
system more efficient. It is also the leading factor that affects the density of other
179
INTERACTIONS
Sun
Fish
(Grass carp)
Rice Plant
u
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en
'£
a
'xO
1
VJ
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u
2
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u j£
=1
I
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00
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u c
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t/3
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jTC/5
Excrement
and Urine
Humans
Figure 1. Flow of energy in the rice-fish ecosystem.
•30
R)
O
O" OT
I
J^
I
a.
180
RICE-FISH CULTURE IN CHINA
biological species and communities. Repeated experiments and comparisons have
demonstrated that grass carp are the best fish to use for rice-fish culture.
In ricefields, grass carp eat a large quantity of weeds. There are more than
30 kinds of common weeds in ricefields. Eleocharis yokoscensis, Hydrilla sp.,
Potamogeton crispus, Vallisneria spiralis, Najas marina, Potamogeton distinctus,
and Lemna minor are eaten by grass carp. In general, weeds can reduce rice yields
by 10-30%. Therefore, if weeds could be totally eliminated, rice yields should
increase by over 10%. Our experiments have indicated that early ricefield without
fish have 13-15 times more weeds than fields with fish. When the fish are
harvested there are about 33-435 kg/ha of weeds, but in ricefields without fish
there are 450-6520 kg/ha of weeds when the rice is harvested, even when weeding
is done three times. The weeds eliminated by grass carp (coefficient of feed 1:80)
provide about 5 kg of fish output. Furthermore, fewer weeds are available to
compete for fertilizer. This stimulates increased rice output, purifies the water, and
improves the environment.
By eating the plankton, weeds, and benthos in the ricefield, the grass carp grow
quickly. The more they eat, the more excrement they discharge. A grass carp
(6.5-13 cm) is estimated to eat 52% of its own weight and to excrete 72% of the
amount of grass it eats. If 400 grass carp are reared for 110 days, fish excrement
amounts to about 26475 kg/ha. This excrement is rich in nitrogen and sulphide and
therefore increases the fertility of the field.
In most cultivation systems, most of the weeds in the ricefield are pulled out and
discarded. This causes a large loss of soil fertility and wastes the solar energy
captured by the weeds. In addition, much of the bacteria, plankton, zooplankton,
and part of the benthos, are usually discharged with the water. This accounts,
either directly or indirectly, for loss of soil fertility and solar energy. From the
point of view of circulation of matter and energy, this is a natural phenomenon that
is unavoidable. However, from the point of view of maximizing bioproductivity,
it is obviously a waste of matter and energy. The raising of fish in ricefields
captures part of the matter and energy that would otherwise be wasted and
transforms them into fish products. At the same time, the fish stimulate rice output.
This is a very economical practice. It is desirable to continue to seek ways to
improve the system and to strive for the highest possible yield using the least
amount of energy and matter to produce the maximum economic returns.
The introduction of grass carp into the ricefield changes the composition of the
biological species and communities and their mutual relationships. Grass carp and
rice become codominant factors in the system.
In the rice-fish ecosystem, nonbiological and biological factors are important.
Growth and development of rice requires light, heat, carbon dioxide, water, and
nutrients. Of these factors, air, water, and nutrients undergo the most dynamic
changes and exert an extremely large influence on the growth of the rice plants.
For example, carbon dioxide is an indispensable raw material for photosynthesis.
During the day, the amount of carbon dioxide in a ricefield with fish is higher than
INTERACTIONS
181
in a ricefield without fish. The fish respire carbon dioxide and feed on plankton
that compete with the rice for nutrients. Generally, there is an increase of
1.5-8.2 mg/L (average 5.1 mg/L) in dissolved oxygen in ricefields with fish. The
minimum level of dissolved oxygen at night is also tolerable for grass carp.
Furthermore the fish tend to raise the dissolved oxygen content level because they
stir up the water and increase the contact between water and air. The activities of
the fish can also make the distribution of oxygen more uniform. Because they move
the soil, the fish also improve the oxygen supply to the soil, which favours the
breakdown of organic matter and reduced material in the soil. This is why many
rice-fish fields that are not exposed to the sun and are not weeded still yield 10%
more than fields in which fish are not reared.
Economic Returns
The first and foremost objective of raising fish in ricefields is to increase rice
output while reducing the labour required for weeding. Rice yields are increased
(by about 10%) in rice-fish fields. In addition, grass carp make full use of the
water and feed provided by the ricefield, harmful insects and other rice pests are
reduced, and the system retains and creates more fertilizer.
This new model of a rice-fish ecosystem is becoming increasingly popular. From
1980 to 1983, Hubei and Hunan Provinces devoted about 33 300 ha of ricefields
to this new model. If the area devoted to raising fmgerlings is assumed to be
2000 ha, the area for growing food fish 2 670 ha, the average output of fmgerlings
4 875/ha, and the output of food fish 525 kg/ha, the two provinces produced
9.75 million fmgerlings and 1.4 million kg of food fish with an output value of
CNY3.2 million. If the increase in rice output is assumed to be 10%, the added
output would be worth CNY1 million. The total value of the rice and fish would
be CNY4.2 million.
In 1984, China had nearly 0.7 million ha of ricefields devoted to rice-fish farming.
This was an increase of more than 80% from 1983. The increase in rice output was
estimated at 285 million kg and the output of fish at 47000 tonnes. Sichuan
Province, which leads the country, devoted 0.3 million ha to rice-fish farming, and
Chongqing City alone reserved 77 330 ha for rice-fish farming. Hunan Province
had 0.2 million ha for rice-fish in 1984, 33.7% more than in 1983. In addition,
many households have reported collecting 7500 kg of rice and 750 kg of fish from
1 ha ricefield.
If these improved methods of raising fish in ricefields could be applied to
6.7 million ha over the next 3-5 years, the rice output could be increased by
2 billion kg and the catch of fmgerlings would amount to 20-50 billion, an
abundant source of supply to raise adult fish. This would help China reach the goal
of producing 4-5 million tonnes of fresh fish each year.
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Fish Culture in Ricefields: Rice-Fish Symbiosis
Xiao Fan48
Fish culture in ricefields originated from natural symbiosis. The accidental
discovery of wild fish in ricefields, and the subsequent catch of both adult fish and
fry, induced people to make use of ricefields for fish rearing. Although the
traditional rice-fish rearing was a modification of the natural system, modern
rice-fish culture has undergone significant development in recent years. The
improved systems have already surpassed traditional methods with respect to
structure, carrying capacity, energy conversion and exchange, and use of materials,
and produced ecological, financial, and social benefits.
Within the rice-fish ecosystem, the plants and animals complement and interact
with each other. The organized food chains produce various materials (living and
nonliving, organic and inorganic, molecular and ionic) that interact with the other
biological, chemical, and physical activities in the ricefield. As a result, the food
chains in the ricefield are rebuilt, soil in the fields is made fertile, the structure of
the water and soil is improved, insect pests are diminished, diseases are controlled,
and mosquitoes and weeds in the fields are reduced.
Rice-Fish Food Web
The long history of rice production in China has affected the natural ecosystem. In
Jiangsu Province, the use of large quantities of poisonous insecticides and chemical
fertilizers since the 1960s has killed rice pests in large areas. However, at the same
time, many other useful organisms have also been destroyed. The use of these
chemicals has changed the characteristics of the natural ecosystem, brought about
an imbalance in the ecology, and caused the gradual disappearance of ecological
advantages. The current rice-fish culture system has reestablished the food chain
offish eating insects and weeds and made it possible to use little or no chemical
herbicides to kill weeds and no insecticides to control insect pests.
Microbes and mosquito larvae
When rice and fish are raised together in ricefields, the plants need fertilizers and
the fish need rich food. In fields where fish are being raised, organic manure
should be used as the basal fertilizer. Only chemical fertilizers that are not
poisonous to fish should be used for supplementary applications. Ammonium
bicarbonate can be used as a top dressing. The ammonium bicarbonate (15-20 kg)
48
Crop Cultivation Technical Station, Department of Agriculture and
Forestry, Nanjing, Jiangsu Province.
184
RICE-FISH CULTURE IN CHINA
should be shaped into balls and placed under the soil in fields covered with
6-7 mm of water.
When manure is applied to the ricefield, benthos and plankton reproduce rapidly
and provide the fish with sufficient food. However, as the fish grow, their need for
food increases, but the availability of food in the fields decreases. A field
investigation showed that the amounts of benthos with fish and without fish were,
respectively, 4.3 g and 12.9 g in mid-June, 8.0 g and 25.1 g in early July, and
5.4 g and 10.2 g in mid-July. The Jiangxi Aquatic Research Institute compared fish
and nonfish ricefields in 1984. There are fewer phytoplankton (625500/ml or
2.4 mg/L of water) and fewer zooplankton (18730000/ml and 3.6 mg/L) in the
fields with fish compared with fields with rice only.
Fish culture in ricefields differs greatly from pond culture because there is a lot of
plankton in the fields and the amount of life decreases gradually. Fewer fish are
stocked in ricefields (30000/ha) than in fish ponds (3 million/ha). A study by the
Hubei Aquatic Institute demonstrated that there was as much as 119 g/m3 of
benthos in ricefields, but only 39 g/m3 in ponds. Moreover, the amount of potential
food increased after the fry had been added to the fields and reached its peak
6 days later. As the fish grow and their appetites increase, the amount of food that
is available begins to decrease. However, in ponds, the benthos began to decrease
sharply only 3 days after the fry were introduced. After 5 days, the amount had
dropped to less than 10 g/m3, which is far too little to meet the needs of the fish.
Fish culture in ricefields also helps eliminate mosquito larvae. In these areas, the
density of larvae in the ricefields was reduced by 50-90%, and in residential areas
the number was reduced by more than 50%. The Chendu Municipal Health Station,
Sichuan Province, surveyed three different areas severely affected by malaria. The
incidence of malaria was 0.01% in 1981 when there was no rice-fish culture, but
in 1982, the incidence dropped to 0.002% after rice-fish culture was started.
Jiadian County Health Station, Shanghai Municipality, monitored the rice-fish
fields of the Chuanjin Aquatic Production Farm from 2 July to 18 October. No
larvae were found in the 18 samples from rice-fish fields, but in the nonfish fields,
larvae were found in every sample. The average per sample was 2.2 larvae (1.7 in
July, 3.3 in August, and 2.1 in September). The use of organic insecticides has
killed large numbers of mosquitoes, but has also given rise to insecticide-resistant
strains. Rice-fish culture is an effective control method for all types of mosquitoes,
including the insecticide-resistant strains.
Weeds
Fish eat many of the weeds in ricefields. Some herbivorous fish loosen the soil by
tilling and digging holes, which uproots the tender roots and stalks of the weeds.
Weeding by fish is timely and frequent and superior to chemical weeding.
When the fry are first put into the ricefields, they feed on plankton. When the
weeds begin to sent out sprouts, the small fish eat these sprouts as well as small
insects. As the fish grow, their ability to eat weeds increases. If there are sufficient
INTERACTIONS
185
fish in the fields, they grow synchronously with the weeds, and control them. Even
the withered rice leaves that fall into the water are eaten. A study by the Zhejiang
Provincial Academy of Agronomical Sciences showed that on 22 August there were
8.0 kg of weeds in a rice-fish field, compared with 30.3 kg of weeds in fields
without fish. On 11 November there were no weeds in the rice-fish field, but
3.07 million green duckweed in the field without fish.
Insect Pests
During the growth and development of rice, insects can be eliminated by fish if the
proper measures are used and the habits of the insects are taken into consideration.
For example, when rice planthoppers develop in the ricefields, they can be driven
into the water if a rope is pulled over the rice plants. Because the planthoppers
pretend to be dead when they fall from the rice plants, they are easily eaten by the
fish.
During the incubation and developmental period for rice borers, a layer of water
should be maintained in the ricefields. Because the rice borers transfer to a new
rice plant after incubation, they will be forced to travel in the water where they can
be eaten by the fish. If pest levels increase, the water level should be raised to
drown part of the stalks and leaves and enable the fish to catch the insects. If the
fish are close to the affected parts of the plant, they will jump to catch the insects.
Insect pests are normally not very serious and can be easily eliminated. Even
during severe infestations, these methods can be used to reduce pest populations.
According to materials published by the Rudong Botanic Protection Station in
Jiangsu Province, in rice-fish fields there were 100 nest of rice planthopper with
984 eggs, compared with 4468 eggs in fields without fish. An investigation in
Rugao County showed that in rice-fish fields there were 30% fewer eggs of the
yellow stemborer, Tryporyza incertulas, the rate of white ears was 50% lower,
there were 50% fewer rice planthoppers, the rate of rice leafrollers was 30%
lower, the rate of white leaves was decreased by 30%, and the number of rice
leafhoppers was 30% lower.
Furthermore, in rice-fish fields, the rice plants are usually very strong and have
good resistance to diseases. The possibility of rice diseases was also reduced
because of the fertile water and good environment, improvements in varieties,
reduction in density, good ventilation, and sufficient light. A study in Chenxian
County, Zhejiang Province, demonstrated that under the same cultivation
conditions, the indices of sheath and culm blight of rice were 11.8, 10.7, and 7.8
in fields without fish, rice-fish fields, and idle rice-fish fields, respectively,
Improvements in Soil and Water Conditions
Soil Fertility
In rice-fish fields, the activities of the fish help mix the manure with the soil. The
fish swallow, digest, and assimilate 30-40% of the organisms living in the fields.
186
RICE-FISH CULTURE IN CHINA
The rest of the organic matter is excreted into the fields and becomes manure. The
fish faeces are a good quality manure that contains 42 % phosphorus (a higher level
than in pigs and cattle manure). Nutrient analysis has shown that are 1.2 times
more phosphates in rice-fish fields than in fields without fish, and ammonia levels
are 1.3-6.1 times higher. The Soil Fertilization Station in the suburbs of Yancheng
County, Jiangsu Province, made a comparison of rice-fish fields with fields
without fish and found that in rice-fish fields where fish had been raised for
2 years, the organic matter level was 1.8% in both fields and the nitrogen content
was 0.12%.49 In ditches with fish, the organic matter content was 1.9% and the
nitrogen content 0.142%, which was much higher than in ditches without fish.
Gases and Nutrients
Under normal conditions, the diffusion of oxygen in water is 10000 times slower
than that in air. This often results in anaerobic conditions at the soil-water
interface. The activities of the fish increase the contact area of the water with air
and profoundly change the gas structure of the water and soil and improve their
physical properties and chemical composition. A gas determination of the soil has
shown that in the fields where early rice is planted and fish are raised, oxygen is
present to a depth of 5 mm in the soil, but not to 10 mm. In fields where late rice
is planted and fish are raised, aerobic condition extend to 8 mm because the fish
are larger and more active. In fields without fish, the surface of the soil-water
interface is normally anaerobic.
Rice-fish culture helps raise rice production by:
•
•
•
Increasing the oxidation of the soil and decreasing the reducing
agents (e.g., H2S, Fe ++ , and Mn ++ ).
Making it impossible for the medium matter (formed as a result of
incomplete dissolution) to mineralize rapidly, to continuously
release energy and produce various NH4+ and PHO4~ ions, and to
renew the humus in the soil.
Allowing the highly concentrated nutrients to spread to the roots of
the rice plants because of the activities of the fish.
Water Temperature and Oxygen Concentration
The water temperature and the conditions for oxygen solution in the ricefields are
better than in fish ponds. The thin layer of water in ricefields puts large areas of
water in contact with the air. There are also 100 times fewer fish in ricefields than
in ponds. This is why fish do not come to the water surface as often in ricefields
as in ponds.
49
The author suggested that there was a difference between the two fields
in both organic matter and nitrogen based on a difference of 0.03%. In the absence
of confidence limits, the editors have assumed there was no significant difference
and changed the text.
INTERACTIONS
187
Fish Diseases
The water in ricefields is usually shallow and fresh and is replenished frequently.
Rice plants absorb fertilizers and purify the water in the fields and, as a result, the
water is continuously fresh and clear (much better than the water in ponds). The
absolute number of pathogenic bacteria in pond water is 2.6 times higher than in
ricefields. The number of bacteria in the water has a direct effect on the number
of bacteria in fish gills. The number of bacteria on one side of the gills of fish in
ponds was 160 x 106; whereas, in fish in ricefields there were only 18.5 x 106. The
change in the bacteria content of the water in ricefields clearly reflects the
incidence of fish diseases. From February to September, the number of bacteria in
ricefields remains stable, and the incidence of fish diseases is low. July, the month
during which fish diseases increase, is the time when the number of bacteria in
ponds is highest.
Because fish live in the water, it is difficult to make any accurate diagnoses of
diseases. Generally, sick fish have no appetite, and medicine cannot be applied or
mixed with fish food. The significance of rice-fish culture is low fish density and
a health environment, which promote normal growth of the fish and prevent stress.
Biological Control of Rice Pests
Insecticides and herbicides are normally used to prevent and control insect pests
and weeds. Part of the insecticide is absorbed by the rice and the rest drops into the
water and soil. In fact, some insecticides are directly applied to water or soil and
consequently contaminate them. For example, in the early 1980s, 9.6 kg/ha of
BHC were used. Some of the BHC entered the soil and water, but most was
dissolved and flowed away. The part that was absorbed as a residue in the crops
was consumed by humans in the rice, and the by-products (bran and straw) were
used as fodder for livestock or fish, whose eggs, meat, and milk were eaten by
people. The residue of the insecticide is being transferred from one organism into
another and in the end accumulates and concentrates in the human body. The
Scientific Experiment Base, Taihu Lake Area, determined that insecticide residues
are highest in rice stalks (4.3 mg) and leaves (5.1 mg) followed by rice husks and
roots (both 3.8 mg). In the rice grain, the highest concentration was found in the
husks and rice bran (3.4 mg). In crude rice, the level is 0.7 mg; in refined rice
0.3 mg.
Tests were carried out in 13 counties of Jiangsu Province in 1983 on the residues
of organochloride insecticides in rice. In samples of middle rice (which accounts
for 31% of the total rice output of the province), the BHC content ranged from
0.01 to 1.06 mg/kg (average of 0.16 mg/kg). Of the samples, 99.1% contained
BHC and 13.7% exceeded the allowable limit. The highest content (1.06 mg/kg)
was 2.5 times more than the allowable limit. In samples of late rice (which
accounts for 49% of total rice production), the BHC content ranged from 0.07 to
1.21 mg/kg (average 0.34 mg/kg). All samples contained residues, and 54%
exceeded the allowable limit.
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RICE-FISH CULTURE IN CHINA
The human body absorbs 34.4% of the insecticide residues in the grain. An
investigation by the Scientific Experiment Base, Taihu Lake Area, found that the
amount of BHC residue a person absorbs each day through grains, edible oil, meat,
fish, and vegetables was 0.58 mg, which was 15 times higher than the maximum
allowable limit suggested by the World Health Organization (0.039 mg per 65-kg
person or 0.0006 mg/kg body weight). The insecticide remains in the fatty tissues
and other organs and causes damage to human health.
Rice-fish culture reestablishes a symbiotic ecosystem, prevents environmental
pollution, and preserves an ecological balance in agriculture. Farmers have made
great achievements in irrigation, rice-strain selection, planting techniques, and fish
culture. Consequently, rice-fish symbiosis has been further developed. At least,
three advantages have been confirmed.
•
•
•
The ecological benefits of rice-fish symbiosis are becoming more
obvious. The elimination of insects and weeds by the fish directly
protects large quantities of living organisms from pesticide use.
Therefore, other useful organisms, natural enemies of insect pest in
particular, survive and reproduce. This extends the possibility of
biological pest control and consolidates the ecological benefits of
rice-fish symbiosis.
Rice-fish culture ensures production of fine-quality fish strains and
market-size fish and increases the income of farmers. Despite the
decrease of planting area, rice unit output increases. The income
from rice-fish culture has increased, and in some cases doubled, the
income from traditional ricefields. This fact can be used to
popularize rice-fish culture.
Rice-fish culture has also reduced soil and water pollution. Polluted
areas become less contaminated or completely unpolluted through
the process of self-purification.
Ecological Effects of Rice-Fish Culture
Pan Yinhe50
Rice-fish culture is a traditional farming system. Since 1978, the area devoted to
rice-fish culture has been expanded several fold, fish production has increased
rapidly, and fish-farming technology has been improved. In many areas, good
harvests of both rice and fish have been achieved (7500 kg of rice and 750 kg of
fish per hectare).
Ni Dashu developed the theory of rice-fish mutualism, in which ricefields are used
for fish culture and fish farming increases rice production. This paper discusses the
ecological effects of rice-fish culture and its economic, social, and ecological
efficiencies.
Effects on the Ecosystem
Abiotic factors (e.g., water, soil, light, heat, and air) and biotic factors (e.g.,
crops, animals, and microorganisms) are closely interrelated and interdependent
and form an ecosystem in the ricefield. In this ecosystem, the biotic community is
transfers and cycles energy and materials.
The ricefield is a typical anthropogenic ecosystem in which rice production is the
main activity. The rice absorbs solar energy, carbon dioxide (CO2), water, and
various nutrients and through photosynthesis produces organic matter and energy,
which are stored and converted into rice and straw. At the same time, wild grasses
and other weeds, phytoplankton, and some photosynthetic bacteria grow in the
ricefields. However, these products are not as useful and complete with the rice.
In the ricefield, zooplankton, herbivorous animals, some insects, and pathogenic
bacteria are the primary consumers. The carnivorous animals are the secondary
consumers, and both bacteria and fungi in the soil decompose organic matter into
inorganic matter.
In ricefields without fish, farmers must carry out regular and labour-intensive
weeding. As a result, there is a heavy loss of soil fertility and solar energy and an
increase of production cost. Because most of the bacteria, phytoplankton, and
aquatic animals in the ricefield cannot be used by the rice, they are lost with the
irrigation water. Moreover, insects, pests, and mosquitoes can reproduce rapidly
and adversely affect both rice and human health.
50
Freshwater Fisheries Research Centre, Chinese Academy of Fisheries
Sciences, Wuxi, Jiangsu Province.
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RICE-FISH CULTURE IN CHINA
When fish are introduced into ricefield ecosystem, the population and composition
of aquatic organisms, and the relationships among them, change. Population
numbers change. Fish, the largest consumers, eat weeds, phytoplankton,
zooplankton, aquatic insects, and other animals. Fish have the greatest effect on
population density and mortality. Because they are primary consumers, grass carp,
common carp, and crucian carp feed heavily on weeds. In China, more than
100 varieties of weeds grow in ricefields. Of these, Hydrilla verticillata,
Ptamogeton crispus, Vallisneriaa spiraalis, Potamogeton matainus, and Lemna
spp. are considered to be good feed for grass carp.
The Biological Department of Southwest Teachers College, Chongqing, Sichuan
Province, stocked fish in ricefields at a rate of 3000 fish/ha (grass carp 30%,
common carp or crucian carp 60%, and silver carp 10%). After 75 days, the fish
had consumed 12465 kg/ha of weeds and only 360 kg/ha remained. If 50% of the
weeds growing in ricefields were consumed by the fish, this would produce
78 kg/ha of grass carp based on a food conversion rate of 1:80. Therefore,
rice-fish culture can effectively eradicate weeds and control the loss of energy
from ricefields.
Rice-fish culture can change the direction of energy flow in the ecosystem. In the
ricefield, the stocked fish transform stagnant energy (e.g., weeds) and possibly lost
energy (e.g., phytoplankton, zooplankton, and aquatic insects) into useable
products (fish and rice). Rice-fish culture also coordinates the interrelationship
between the biotic and abiotic environments. In ricefield ecosystem, rice requires
light, heat, air, water, and nutrients for its growth. Air, water, and nutrients have
the greatest impact on rice production. Because the ricefield is usually flooded, the
normal water requirements of rice can be ensured. However, an inundated field
does not favour root development of the rice. Under inundated conditions,
dissolved oxygen (DO) from the surface water can only be supplied to soil through
diffusion and transpiration. In general, the level of dissolved oxygen in the surface
water varies diurnally with algal photosynthesis during the day. Dissolved oxygen
usually reaches a maximum (12-14 mg/L) when light is adequate. However, more
than 95% of the DO is taken up by various organisms in the surface water and little
of the DO diffuses and permeates into the soil.
Under these circumstances, as temperature rises, soil reduction increases and
reducing substances (e.g., methane, organic acid, and hydrogen sulphate) increase
and decay rice roots. This problem is normally solved by sun-drying the ricefield.
However, as fish move about in the ricefield, they increase contact between the air
and water. This increases oxygen content throughout the field. In addition, the fish
disturb the soil, which accelerates decomposition of organic matter and reduces the
concentration of reducing substances.
Although sun-drying and weeding are sometimes not practiced in rice-fish fields,
rice production is higher than in fields without fish culture. From the viewpoint of
aquaculture, the total dissolved oxygen level is low in rice-fish fields (less than
4 mg/L in the early morning). However, fish mortality due to the oxygen depletion
has not been reported.
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Table 1. Nutritional composition of four types offish excreta (percentage dry weight).
Fish Excreta
N (%)
P (%)
Grass carp
1.102
0.426
Common carp
0.824
0.671
Crucian carp
0.760
0.403
Silver carp
1.900
0.581
Generally, the ricefield has a pH of about 7.0, which is optimal not only for the
growth of rice and fish, but also for the reproduction of natural food organisms.
Fish also have a positive effect on soil fertility because of the accumulation of fish
excreta, which has a high nutritive value (Table 1). Silver carp excreta was the
best, grass carp and common carp excreta second best, and crucian carp excreta the
poorest. The concentrations of N and P in the fish excreta were higher than in pig
and cow manure, similar to those of night soil and sheep manure, but lower than
those of chicken and rabbit manure.
The daily manure production of one fish has been estimated to be about 2 g. If the
average stocking density was 3000 fish/ha (stocking size about 100 g), 6000 g of
fish manure would be produced every day. This would amount to 450 kg/ha of fish
manure if the fish were reared for 75 days. The N content of the soil was reduced
at the end of the production season by 1.1 % in the ricefield with fish and 12% in
the field without fish. The fish are able to transform the energy in the ricefield
ecosystem and enrich the soil.
Fish can also minimize outbreaks of diseases and insect pests and reduce the
application rate of pesticides, which can pollute water, soil, rice, and fish. When
fish are cultured with rice, the main primary producer (rice) and consumer (fish)
are combined to form a symbiotic rice-fish ecosystem.
In rice-fish fields, the rice reduces sudden changes in water temperature caused by
sunlight, adjusts and stabilizes water temperature and quality, and, therefore,
provides an environment that is conducive to the reproduction of natural
organisms. Because the fish consume phytoplankton, zooplankton, and weeds that
compete with rice, they play an important role in increasing and stabilizing soil
fertility, eradicating harmful insects and pests, recovering lost energy, and
adjusting energy flow. In the symbiotic rice-fish ecosystem, the mutualism
between rice and fish is fully exploited to provide high-quality products and good
environmental conditions.
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RICE-FISH CULTURE IN CHINA
Efficiency of Rice-Fish Culture
Economic Efficiency
Rice production is increased by 5-15% in rice-fish culture. Experiments in many
locations have demonstrated that rice growth is improved in rice-fish fields. In
particular, the rice developed evenly, tillering is improved, more rice grains are
produced, ears are heavier, and the rate of false grains is lowered.
Rice-fish culture can also increase the production value of ricefields. Based on the
collection of nation-wide information, net profit can be increased by
CNY300-750/ha. Profits can be even higher (CNY1500-15 000/ha) if fry are
reared in the ricefields. The economic efficiency is increased because the fish have
a high value.
Fish can also help eradicate weeds, minimize the loss of fertilizer, and reduce
outbreaks of insects and pests. Therefore, fertilizers, pesticides, and labour can be
saved. In experiments in Taoyuan County, Hunan Province, the concentration of
quick-acting N and P in rice-fish fields was increased by 10% and 124%,
respectively, compared with fields without fish. Fish are able to reduce populations
of rice hoppers and rice leafrollers 2-6 times. As a result, the application
frequency and quantity of pesticides can be decreased. Moreover, based on
investigations in Jiangxi, Guizhou, and other provinces, about 120-180 labour
units per hectare can be saved with integrated fish culture. In some places, farmers
do not plough the field when rice-fish culture is practiced. This further reduces the
inputs needed for rice planting, and therefore, reduces production cost and
increases the economic efficiency of rice cultivation.
Social Efficiency
Rice-fish culture expands the area for fish culture and produces more fish
products. Rice-fish culture also produces (with less input) increased numbers of
large-size fingerlings for the development of fisheries in ponds, reservoirs, and
rivers. If the ricefield is used to culture food fish, average production is
300-750 kg/ha (maximum 750-2 250 kg/ha). This practice is an effective way to
increase fish production in hilly areas. At the same time, rice-fish culture
effectively increases the income and living standard of farmers, particularly those
living in hilly, rural areas.
Rice-fish culture also increases rice production. It makes multiple use of the
ricefield to maximize the utilization of land and water resources. The proper
combination of crop production and aquaculture will effectively promote the
transformation of the structure of rice production.
Ecological Efficiency
In rice-fish culture, harmful insects and pests are greatly reduced. Therefore,
pesticide application can be reduced or eliminated, and toxicity accumulation is
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minimized. This is beneficial to human health and the ecological balance of the
environment. For example, the number of predators of rice pests is higher in
rice-fish fields without pesticides than in fields without fish and with pesticides.
Rice-fish culture also improves the environment and reduces infectious diseases of
livestock and humans. In ricefields, mosquito larval, maggots, snails, and leeches,
which are the intermediate host of malaria, encephalitis, dysentery, blood fluke,
and filaria, reproduce rapidly. Fish, particularly common carp, crucian carp,
tilapia, and other omnivorous fish, consume and eradicate these pathogenic
parasites and minimize the infestation rate of human beings, thereby creating an
improved living standard and a better level of health for the farmers.
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Ecological Mechanisms for Increasing Rice and Fish
Production
Pan Shugen,51 Huang Zhechun,52 and Zheng Jicheng53
Experiments plus production practices have demonstrated that rice and fish
production can be increased by raising fish in ricefields. Mechanisms to increase
rice and fish production have been developed based on experiments and
investigations in Sanming Prefecture, Fujian Province.
Ecological Environment
Physical and Chemical Environment
In a double-cropped field in Ningua Sanming, Fujian, the mean water temperature
from May to October was 27.5°C and the accumulated temperature was 5 055.6°C.
The highest temperature was 38°C on 27 July and the lowest was 17.5°C on
26 October. Compared with air temperature, the mean water temperature was
1.3°C higher and accumulated temperature was 231.1°C higher. Other
observations in Yongan from 14 August to 30 November showed that the mean
water temperature in a late ricefield was 25.5°C. Because the water was shallow,
the temperature rose rapidly and sunshine reached the soil directly. Therefore, the
water temperature was similar in the upper and lower layers, which favoured
decomposition of organic matter.
In Ninghua, water levels in the fields used for rice-fish cultivation varied from 3 to
10 cm, and no water remained in the field after the field was drained field and the
crop matured. The water level in the field for rice-fish rotation varied from 60 to
80 cm. The water demand for a field producing 7500 kg/ha of rice was 36000 m3.
Water for irrigation varied from 9 000 to 12 000 m3. Because of water is shallow
and there is a great exchange of water, the environment for fish was limited, and
fertilizer and food flowed away easily.
The dissolved oxygen level was high in the fields because of the water exchange
and the large amount of oxygen released by the rice and phytoplankton. In Ninhua,
51
Jimei Fisheries School, Jimei, Fujian Province.
52
Ninghua Popularization Centre of Fisheries Techniques, Ninghua,
Sanming Prefecture, Fujian Province.
53
Yong'an Popularization Centre of Fisheries Techniques, Yong'an, Fujian
Province.
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RICE-FISH CULTURE IN CHINA
the average dissolved oxygen level varied from 3.9 to 5.6 mg/L (maximum
12 mg/L at noon on sunny days). Fish in the ricefields have a higher metabolism
and a higher rate of food utilization than fish cultured in ponds.
Based on determination from many locations in Sanming, the pH of water in
ricefields varies from 6.3 to 6.8. Most of the soils in the mountainous districts of
Fujian are red, and the water in the fields is acidic.
In Ninghua, the rate of biological oxygen demand (BOD) in fields with fish was
33.4 mg/L; ammonia nitrogen 0.80 mg/L, nitrate nitrogen 0.68 mg/L, phosphate
0.06 mg/L, hardness 0.42 mg equivalent weight/L, and alkalinity 0.65 mg
equivalent weight/L. These parameters are comparable with the levels found in rich
water in reservoirs. This is why the fish cultured in ricefields have a high level of
productivity. In Shangmin, there was less phosphate and lower hardness in the
ricefields, and because of uneven fertilizer application and greater water exchange,
the richness and stability of the fertilizer were decreased.
Energy
Sunlight is the most important energy source in ricefields. Based on data from
meteorological observations, annual light duration ranged from 1708 to 1 898 h
and total irradiation from 91.3 to 106.4 kcal/cm2. The rice used less than 1% of
the light energy, therefore before the rice covered the field, most of energy was
used by weeds and phytoplankton. This means that the light is also the major
energy source that will eventually be used by the fish in the ricefields.
Rice roots, straw, flowers, and grain are the products of photosynthesis, and much
of them remain in the field. In Ninghua, experiments indicated that in 1 ha of
ricefield there was 48210 kg of roots, 17745 kg of stubble, and 14385 kg of
straw. Straw contains 9-13% cellulite, 1.6-3% potassium, and 35-40% cellulose,
which favours growth of microorganisms and diatoms. Results from pollenchamber studies show that 1400-1500 grains are produced per flower, and the
blossoms drop to the field after the flowers are fertilized. In Ninghua, two seasons
of rice blossoms amounted to 1559 kg/ha. Rice blossoms are rich in protein. There
is a saying the more fragrant the rice blossoms, the fatter the carp. During harvest,
about 3-5% of the grain drops into the field. Rice-plant trash was 81000 kg/ha,
or about one-quarter of the products produced by photosynthesis. These products
provide organic matter and fertilizer for rice-fish culture.
In ricefields producing 7500 kg/ha of rice, the demand for nitrogen is
120-188 kg/ha, phosphorus 60-113 kg/ha, and potassium 135-270 kg/ha. In
Shangmin, the amount of fertilizer applied to a field producing 7 500 kg/ha of rice
was 1125 kg/ha ammonium carbonate, 450 kg/ha calcium superphosphate, and
1200 kg/ha organic fertilizer. About one-third of the volatile section was absorbed
by the rice and about half was drawn into the soil and dissolved in the water to
become nutrients for food organisms. This is the major source of fertilizer for
rice-fish culture.
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Food Organisms
In the ecological environment of the ricefield, there are many organisms besides
rice and fish. Investigation in Ninghua indicated that there were 25 families and
433 species of vascular plants in the ricefields. In the late ricefields without fish,
the amount of biomass was determined at three times (before harvest, after the field
was drained, and when the grain was filled). The amount of biomass averaged
6045 kg/ha, and most of the species were suitable food for fish.
Both the number of species and the quantity of plankton in ricefields were reduced
compared with levels in fish ponds. Based on investigations in Jianning, Sanming
Prefecture, there were 6 phyla and 61 genera of plankton, of which 20 genera were
diatoms, 29 genera were green algae, 5 genera were blue-green algae, 1 genus was
golden algae, and 1 genus was Dinophyceae. There were also 3 species of
protozoa, 10 species of rotifer, 1 species of Cladocera, and 2 species of copepods.
The concentration of phytoplankton was 15-65/L; zooplankton was 900-2 800/L.
The recommended fertilizer rate and time of application also encouraged rapid
plankton growth. Biomass reached 75-119 mg/L, which was 4-6 times higher than
in fish ponds and easily satisfied the food requirements of fish fry.
Based on investigations in Jianning, there were 22 species of benthos, of which
17 species were insects, 3 species were gastropods, and 2 species were nematodes.
Studies in Ninghua showed that the biomass of benthos can reach 109.3 kg/ha. All
these species are good food for fish.
In fish stomachs, organic detritus was found most frequently. In Jianning, 42 carps
were dissected and large amounts of organic detritus were found in all fish (1 g of
organic detritus contains 450 bacteria, which weigh about 5% of organic detritus).
Bacteria are rich in protein and are eaten by zooplankton and benthos animals as
well as by fish. Bacteria play an important role in increasing rice and fish
production.
Pests and Diseases
Fish diseases are rare in rice-fish culture because the water is clear and the oxygen
content is high. In addition, the lower stocking density and rich natural food
produce strong fish that are more disease resistant. Fish pathogens are rarely seen
in ricefields. Based on investigations by Han Xianpu, there were 4100 bacteria per
millilitre in ricefields compared with 8 800/ml in fish ponds. Pathogenic bacteria
were 1.6 times lower than in fish ponds. There were no significant differences in
the number of bacteria on the fish bodies between the field and fish ponds.
However, in ricefields, the number of bacteria in the fish gills was 1 850/ml,
compared with 16000/ml in fish ponds (7.6 times lower). Therefore, rice-fish
culture is an effective natural method of protecting fish (especially carp) from
disease.
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RICE-FISH CULTURE IN CHINA
Because the water is shallow in the fields, it is difficult for fish to escape from
predators (e.g., centipedes, leaches, birds, snakes, frogs, rats, and otters). In
addition, the narrow levee of the ricefleld can easily collapse if rats and eels dig
holes in the bank. Fish can easily escape from ricefields if there is flooding;
therefore, fish survival is not as high.
According to this analysis, organic matter and food organisms will provide more
than 20 kg of natural fish productivity. In 1983, in Ninghua, a 21.9-ha field was
used for rice-fish cultivation. Production averaged 316 kg/ha (without feeding).
In Jianning, fish production from 20.6 ha of ricefields was 282 kg/ha (without
feeding). In 1985, in Ninghua, Yongan, 133.3 ha of ricefields stocked with fish
produced 720 kg/ha with the addition of some fertilizer and weeds.
These studies demonstrate that ricefields offer clean water, enriched food, less
disease, and can provide over 300 kg/ha of natural fish productivity. However,
there are still some problems to be solved (e.g., shallow water, unstable water
quality, predators, and easy escape).
Increases in Rice Production
Controlling Weeds and Fertilizing Fields
Weeds compete with rice because they also need carbon dioxide, water, and
nutrients for photosynthesis. Fish stocked in ricefields eat weeds continually and
effectively control weed growth. Carp eat weeds at the rate of 30-50% of their
body weight, and 1-year-old carp eat 25 g of weed seeds (about 4000 seeds) a day.
Experiments during the late season in Ninghua showed that in ricefields stocked
with fish, weed weight averaged 161.7 g/m3, compared with 604 g/m2 in the
control field.
In Yongan, in a ricefield with rice-fish rotation, weeds numbered 23.3/m2,
compared with 137.1/m2 in the control field (a decrease of 4.5 times). In Ninghua,
weeds in the late-crop field stocked with fish decreased 4 425 kg/ha compared with
the control field. Using the value of 3.3% as the mean amount of nitrogen needed
by vascular plants, these reductions would preserve 9.7 kg of total nitrogen. In
addition, fish kill weeds continually and more efficiently than humans.
Accumulating Fertilizer and Increasing Fertility
Much of the food that fish consume is excreted and becomes a fertilizer for the
rice. Only 30-40% of the weeds are digested by the fish, the remainder is excreted
as faeces and urine. If a fish excretes 2% per day of its body weight as faeces, a
field used for rice-fish culture that produces 315 kg/ha of fish without feeding for
180 days would produce 567 kg of faeces.
A field used for rice-fish rotation that produces 1845 kg/ha (Yongan) for 120 days
would produce 2 205 kg of faeces. Carp faeces contain 1.1% nitrogen and 0.4%
phosphorus. In rice-fish culture, fish faeces contribute the equivalent of 31.5 kg
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of ammonium sulphate and 13.5 kg of calcium superphosphate. In rice-fish
rotation, fish faeces contribute the equivalent of 121.5 kg of ammonium sulphate
and 52.5 kg of calcium superphosphate.
Soil tests in Yongan in 1982 showed that with rice-fish rotation, organic matter,
total nitrogen, and total phosphorus increased by 0.6%, 0.03%, 0.001%
respectively, compared with the control field. Soil tests in Ninghua in 1984
demonstrated that rice-fish cultivation increased organic matter by 0.09%, total
nitrogen by 0.04%, total phosphorus by 0.38%, available nitrogen by 22 ppm, and
available phosphorus by 2 ppm compared with the control field. Analysis of the
water in the ricefield showed similar results. In fields stocked with fish, BOD
increased by 7.49 mg/L, ammonium nitrogen by 0.14 mg/L, and phosphate by
0.032 mg/L compared with the control field.
Loosening of Soil and Promoting Fertility
When submerged in water, the soil of a ricefield experiences slow breakdown of
organic matter, thorough decomposition of vegetation, stable fertility, and less loss
of nutrients. If submerged for a long time, the soil has intensive reduction and
anaerobic decomposition, which produce large amounts of organic acid. These
acids are unfavourable for rice roots. When soil reduction is intense, methane and
hydrogen sulphide are produced and damage rice roots. Therefore, the field must
be tilled and dried during the middle growth stage to intensify soil oxidation and
control the formation of reducing substances.
Fish move about in the ricefield looking for food. Consequently, they enhance
contact between the water and air and increase the dissolved oxygen level. As the
fish move, they stir the anaerobic layer of the soil. This accelerates the breakdown
of organic matter and favours root growth. When rice roots draw nutrients from
the soil, they decrease the concentration of nutrients around the root. The plants
depend on infiltration of soil water that contains nutrients. This movement to the
rice roots occurs very slowly. As the fish swim, they stir nutrient evenly and
accelerate infiltration of nutrients into the soil. This helps the roots obtain nutrients
more effectively.
Controlling Rice Pests
Fish eat many pests (e.g., rice plant hopper and leafhoppers) when they drop into
the water. Some pests (e.g., rich borers, rice root worms, and snout beetles)
damage rice after they travel through the water. While in the water, they are easily
eaten by fish. Fish also help control bacterial diseases (e.g., spotted wilt disease)
because they eat the cysts of the bacteria. An investigation in Ninghua in 1984
indicated that leafhoppers and rice planthoppers in ricefields stocked with fish were
reduced by 16%, yellow rice borer by 17%, and spotted wilt disease by 52%
compared with the control field. In Jianning in 1985, spotted wilt disease was
reduced by 28-51%, withered paddy by 15-32%, and rice planthoppers by
70-84% in the field stocked with fish.
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RICE-FISH CULTURE IN CHINA
These factors combine to increase rice production in fields stocked with fish. In
1984 in Ninghua, the height of the rice increased by 2%, effective rice ears by
14%, number of grains by 9%, rate of fruit bearing by 2%, weight of 1000 grains
by 4 %, and yield by 7.1 % in the field used for rice-fish culture. Similarly in
Yongan in 1983, the height of the rice increased by 6%, effective rice ears by
12%, number of grains by 2%, the rate of fruit bearing by 0.4%, the weight of
1000 grains by 2%, and yield by 18% in rice-fish fields.
Conclusion
Ricefields provide an ecological environment that is suitable for both rice and fish.
When ricefields are stocked with fish, the fish eat food organisms and organic
detritus. Energy and material that used to be lost are captured and converted into
fish protein. Fish kill pests and weeds and excrete faeces to the field. In addition,
fish movements promote air exchange and distribution of fertilizer.
There are contradictions between rice and fish when applying fertilizer and
pesticides and draining fields. In recent years, these contradictions have been
resolved by digging ditches and pools, applying fertilizer to all layers of the field,
and applying pesticides that are highly efficient and have low toxicity.
In ricefields used for fish culture, there are still some problems (e.g., shallow
water, excessive water exchange, unstable water quality, predators, and fish
escape). Therefore, further improvements are still required.
Rice-Azolla-Fish Cropping System
Liu Chung Chu54
China has a long history of raising fish in ricefields. However, fish yields are low
because of difficulties in applying feed to the large areas of fish-raising fields.
Azolla is a small aquatic plant that contains abundant nutrients because it can fix
atmospheric nitrogen, carry out photosynthesis, and uptake nutrients from its
surrounding environment through its root system. It is also an excellent feed for
fish. Azolla is rich in the amino acid arginine, which may play an important role
in fish growth (Tables 1 and 2). Azolla grow quickly, produce high yields, are a
suitable size for fish grazing, do not require harvesting or chopping, and can grow
in the ricefield. To increase its ecological and economic benefits, a rice-azolla-fish
cropping system was established in 1981. These experiments have indicated the
potential of this cropping system.
The Role of Azolla
Fish Feed
Both grass-feeding and omnivorous fish eat azolla. Grass carp (Ctenopharyngodon
idella) and nile tilapia (Oreochromis niloticus) consume the equivalent to more than
50-60% of their body weight in azolla each day. The amount of azolla consumed
by the common carp (Cyprinus carpio) increases with increased size.
Feeding experiments with four fish species were conducted by the Soil and
Fertilizer Institute, Hunan Academy of Agricultural Sciences. The feed conversion
coefficient of azolla was 49.0 for grass carp, 52.1 for tilapia, 31.2 for Hunan
crucian carp, and almost zero for lotus carp. The weight gain for these species was
174 g, 134 g, 36 g, and 5 g, respectively. There were high levels of 15N-labelled
azolla in the internal organs of nile tilapia and low 15N-labelled azolla levels in the
external organs at the start of the experiments. However, the level of 15N-labelled
azolla in the internal organs gradually decreased, whereas the level of 15N-labelled
azolla in the muscles greatly increased (Table 3). After uptake of 15N-labelled
azolla for 96 h, 15N recovery in the intestine, stomach, and liver decreased from
10.3% to 1.0%, 1.6% to 0.2%, and 2.4% to 0.7%, respectively. A similar trend
was found in other internal organs. In contrast, 15N recovery in muscles was 6.3%
at 18 h and increased to 10.1% at 96 h. Metabolism balance estimates were
obtained from a 4-day nile tilapia experiment. The amount of nitrogen accumulated
54
National Azolla Research Centre, Fujian Academy of Agricultural
Sciences, Fuzhou, Fujian Province.
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RICE-FISH CULTURE IN CHINA
Table 1. Nutrient contents (% dry weight) of various green feeds.
Green Feed
Dry Crude Crude Crude N-free
Matter Protein Fat Cellulose Extract
Azolla
Ash
Ca
P
6.93
25.0
3.1
11.5
34.9
17.3
1.52 0.96
Eichhorinia sp.
5.04
20.3
1.8
13.8
32.8
22.6
1.19 2.90
Trifoliumsp.
11.57
16.6
4.0
26.1
34.4
11.3
1.24 0.82
Sweet-potato
vine
12.27
17.7
3.1
13.9
41.5
9.8
1.81 0.43
Astragalus sp.
11.43
20.8
5.7
23.2
34.9
7.5
0.79 0.62
Grass
23.60
14.1
1.4
20.3
44.1
14.0
0.72 0.29
Pennisetum
purpuremu
16.10
9.7
1.3
29.3
37.8
14.5
0.48 0.52
fillicuhides
Source: Guangdong Academy of Agricultural Sciences.
Table 2. Amounts of 10 essential amino acids contained in various green feeds for fish
(dry matter, mg amino-acid/100 g protein).
Azolla
filiculoides
Eichhomia
Pistia
shatiotes
SweetPotato Vine
Astragalus
sp.
Trifolium
sp.
Arg
6.84
6.45
6.86
2.00
6.54
5.60
His
2.28
2.36
2.68
1.37
3.13
2.65
He
4.56
3.79
3.87
1.36
4.62
4.28
Lea
8.64
6.89
8.45
4.04
8.32
7.65
Lys
5.48
6.75
7.99
0.28
6.59
6.27
Met
1.40
1.87
1.56
0.72
1.29
1.33
Phe
4.68
4.58
4.89
2.36
5.00
5.12
Thr
5.00
3.84
5.05
2.37
3.85
4.39
Trp
7.44
11.92
7.53
8.55
8.75
8.19
Val
4.88
4.04
5.00
L88
5.91
5.48
Source: Guangdong Academy of Agricultural Sciences.
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203
Table 3. Recovery of 15N-labelled azolla from various organs of nile tilapia.
15N Abundance (%)
Organ
18-h Sampling
96-h Sampling
Head
-
3.22 ±1.10
Skeleton
-
3.73 ±0.08
Muscle
6.34 ±1.17
10.05 ±1.17
Scales
—
0.65
Brain
-
0.05 ±0.031
Ovary
-
1.31 ±1.08
Intestine
10.30±3.45
0.97±0.51
Stomach
1.64±0.80
0.24±0.21
Liver
2.36±0.80
0.68 ±0.11
Heart
0.064 ±0.0017
0.035 ±0.007
Blood
0.455 ±0.329
0.60±0.14
Spleen
0.28 ±0.22
0.06
Gall
0.219±0.010
0.24±0.23
Gill
2.96 ±0.50
L35
Source: National Azolla Research Centre, Fujian Academy of Agricultural Sciences.
by the tilapia represented 30% of total azolla N. Tracer techniques (using 15N) were
used to obtain a better understanding of nutrient abundance in fish faeces. During
the 96-h excretion period, the highest determined 15N level was 3.8%, the lowest
was 2.1%. This was much lower than the level of 15N in the azolla fed to the fish.
This reduction was probably due to the dilution of 15N from the azolla by the other
nitrogenous matter excreted from the alimentary canal of the fish (which includes
digestive juice, sloughed cells from the stomach, and azolla). These results
demonstrate that azolla-N accounts for 30% of N in fish faeces. Because another
30% of total azolla-N accumulates in the fish body, it can be estimated that azollaN is about 60% digested by the fish (N may also be excreted into the water in the
form of urine, as excretions from the body surface, as falling scales, or as matter
exchanged by the gills). The utilization of 15N from azolla in the rice-azolla-fish
system is increased to 67.8% (Table 4); whereas, the rice-azolla treatment using
15
N-labelled azolla as a top dressing at the maximum tillering stage had a utilization
rate of 46.1%.
204
RICE-FISH CULTURE IN CHINA
Table 4. Utilization ratio of 15N-labelled azolla.
Utilization Ratio of 15N-Labelled Azolla (%)
Treatment
By Fish
By Rice
Total
38.24
29.52
67.76
Rice-azolla
(15N-labelled azolla, basal)
—
46.06
56.06
Rice-azolla
(15N-labelled azolla, top dressed)
-
51.60
51.60
Rice-azolla-fish
(as fish feed)
Source: National Azolla Research Centre, Fujian Academy of Agricultural Sciences.
Table 5. Effects of azolla on fish yields.
Fish Yield (t/ha)
Species
With Azolla
Without Azolla
Weight of Fish (g)
With Azolla
Without Azolla
Silver carp 0.35 0.15 600 450
Grass carp 0.15 0.15 150 130
Nile tilapia
0.54
0.40
125
100
Source: National Azolla Research Centre, Fujian Academy of Agricultural Sciences.
Fish Yields
In the traditional rice-fish system, fish grow slowly because there is insufficient
feed. This problem can be solved by introducing azolla. Experiments over 3 years
demonstrated that the rice-azolla-fish system will produce fish yields of
1 000 kg/ha. As well, yields can be further increased by using some other
techniques (e.g., the polyculture of grass carp and nile tilapia). Fish yields were
almost doubled compared with the traditional system for silver carp (Table 5). The
yield of edible fish is also raised. The rice-azolla-fish system increased farm
income by about CNY1954/ha.
Effect on Rice Yield
The rice-azolla-fish system provides an excellent growing environment for rice,
fish, and azolla. Because of the high amount of organic fertilizer provided by fish,
the rice grows well (Table 6), and because the fish eat azolla, rice pests, and
weeds, the use of chemical pesticides can be reduced. However, the environment
INTERACTIONS
205
Table 6. Agronomic characteristics of rice grown under different cropping systems.
No. of
No. of
Filled
No. of Effective Grains
Seedlings Panicles
per
per Hill per Hill Panicle
Season Treatment
Filled 1000Grain Grain Theoretical
Rate Weight
Yield
(%)
(%)
(kg)
Early Single rice 11.38 10.13 47.0 65.9 22.4 4288.5
rice
Late
rice
Rice-azolla
12.25
11.38
33.5
65.2
21.7
4255.5
Rice-fish
13.25
12.00
44.8
65.6
23.2
4969.5
Rice-azolla-fish
11.75
10.63
50.0
69.7
23.5
5589.0
Single rice
7.25
7.25
112.1
76.9
28.8
6930.0
Rice-azolla
7.67
7.67
119.4
76.5
29.6
8085.0
Rice-fish
8.08
7.92
113.2
76.5
29.0
7656.0
Rice-azolla-fish
9.33
7.32
116.8
75.7
29.7
9324.0
Source: Fujian Academy of Agricultural Sciences.
Table 7. Growth of weeds in the rice-azolla-fish system.
Weeds Weeds
(g)
Cropping System per m2
Average
Weight
(g/m2)
Weed
Weight
(kg/ha)
Remarks
Rice (compared)
48
446
454
4 500
Floating azolla species 80%
Waterweed species 20%
Rice-azolla
9
62
64
630
Floating azolla species 50%
Waterweed species 25%
Rice-fish
—
—
—
—
Others 25%
Rice-azolla-fish
—
9
9
112
Weeds
created by the rice-azolla-fish system is also conducive to the survival of the
natural enemies of rice pests (e.g., spiders and black ants). This further decreases
pesticide requirements. For example, during a plant leafhopper outbreak in Fuqing
Country, Fujian Province, in 1984, four applications of pesticides were required
in traditional rice-growing systems and provided incomplete control. In contrast,
only one application was required under the rice-azolla-fish system. Observations
from 1983 to 1986 indicate that the rice-azolla-fish system effectively suppresses
weeds and rice pests (Table 7).
206
RICE-FISH CULTURE IN CHINA
SoU Fertility
In the rice-azolla-fish system, plant nutrients are provided by decomposition of
azolla and by excretion of fish faeces. Improvements in fertility were greater in the
ditches than on the field surfaces (Table 8). This can be attributed to the effect of
the fish in the system, especially the role played by fish faeces in improving soil
fertility. The rapid increase of available potassium is also apparent, which
demonstrates the capability of azolla to enrich potassium levels. Although the rice
yields from this system are similar to traditional systems, an extra 375-600 kg/ha
of fish are harvested. The fish decrease the amount of mineral fertilizer required
by the rice plants, maintain or improve soil fertility, and create an excellent
ecological environment.
Implementation of the Rice-AzoIIa-Fish System
Field Design
Two forms of field design can be considered for the introduction of the
rice-azolla-fish system. The first method involves digging pits and ditches in a
traditional ricefield and transplanting rice seedlings in accordance with normal
spacing practices. In the second method, rice seedlings are transplanted on ridges
and fish are raised in the ditches between the ridges. The selection of fields is
particularly important for both designs. In both cases, the field must have sufficient
water and have good controlled of irrigation and drainage. In most cases, a
rectangular pit(s) that occupies 5 % of the total ricefield area will suffice. In all
cases, pit depth should be between 1 and 1.5 m. Ditches are 30-50 cm deep,
40-50 cm wide, and occupy 3-5% of the total ricefield area. The field is designed
according to the desired yields of rice and fish. In another words, to harvest more
fish, pits and ditches should occupy more area, field ridges should be wide and
thick to prevent fish escape, and drainage openings should provide for good
irrigation.
Combinations of Fish Species
Fish species should be chosen in accordance with their feeding efficiency. For
example, grass carp are unable to fully digest cell walls of plants because their
alimentary canal lacks cellulase. Consequently, they excrete feed residues into the
water along with fish faeces. Nile tilapia excretions stimulate the propagation of
plankton. Under these conditions, pure cultures of either species do not use azolla
efficiently. However, this problem can be solved if a mixed culture (polyculture)
of silver carp and common carp with grass carp, nile tilapia, and common carp
(ratio of 100:300:100:7500 fmgerlings/ha) is introduced after the rice seedlings are
transplanted.
Growing Season for Azolla
The key technological problem in the rice-azolla-fish system is a healthy and
sufficient azolla biomass. Two methods are recommended to increase the azolla
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207
Table 8. Characteristics of soil fertility under various rice-cropping systems.
O.M.
(%)
Total Total P Alkali
K
P205
N (%) P20S (%)
N
(ppm) (ppm)
3.748
0.219
1.20
200
91
6.9
3.917
0.223
1.20
205
244
6.9
Rice-fish
3.896
0.226
1.19
218
86
8.5
Rice-azolla-fish
3.972
0.239
1.35
216
172
8.8
Single rice
3.928
0.228
1.29
202
172
5.2
Rice-azolla
3.977
0.239
1.36
219
253
6.0
Rice-fish
4.272
0.272
1.53
198
334
5.6
Rice-azolla-fish
4.548
0.283
1.59
219
494
5.3
3.677
0.205
0.12
158
88
7.3
3.784
0.203
0.12
157
120
7.5
Rice-fish
3.849
0.198
0.14
172
172
8.2
Rice-azolla-fish
3.948
0.247
0.14
182
165
10.3
Single rice
4.107
0.239
0.13
200
157
6.9
Rice-azolla
4.108
0.206
0.14
209
197
7.4
Rice-fish
4.825
0.289
0.15
298
192
8.4
Rice-azolla-fish
4.954
0.296
0.16
264
259
9.1
Season
Site
Early
rice
Field
Single rice
surface
Rice-azolla
Early
rice
Late
rice
Late
rice
Ditch
Treatment
Field
Single rice
surface
Rice-azolla
Ditch
Source: Central Laboratory, Fujian Academy of Agricultural Sciences.
biomass: increase the space between rice rows to give the azolla sufficient room
to grow, and prolong the propagation period to ensure the fish have sufficient food
to eat. Polyculture of different azolla species and other watenveeds can also be
introduced. Various kinds of watenveeds (e.g., Lemna minor and Wolffia arrhiza)
can be cultivated in the ricefield to supply fish feed in June and July (this method
is called rotational cultivation of azolla).
Field Management
Water management is the most important factor in the rice-azolla-fish system.
During the early stage of rice growth, fmgerlings can swim freely in the shallow
water, which is good for tillering of early rice. Later, the larger fish need deeper
water. At this time, the water temperature can sometimes reaches 40°C, and it is
necessary to keep the irrigation water at the depth of 8-10 cm.
208
RICE-FISH CULTURE IN CHINA
Fertilizer should be applied principally as green manure supplemented with
chemical fertilizers. Basal application is stressed and should account for 70% of the
total amount of fertilizer used. Deep placement of granules of N fertilizer decreases
the loss of N, which benefits both fish and rice. To prevent disease and pests, it
may be necessary to apply some insecticides, but the type, application rate, and
application methods must be suitable for fish. Biological control methods are
preferred.
Effect of Fish on the Growth and Development of Rice
Li Duanfu,55 Wu Neng,56 and Zhou Tisansheng56
A rice-fish system was investigated for 3 years to determine its effect on the
growth and harvest of rice and the income to farmers. A ridge-ditch cropping
system was used.
Method
An experimental ricefield of average fertility was plowed and levelled. A
ridge-ditch system was used. The ditches were 20 cm wide and 30 cm long and the
ridges were 30 m long and 50 cm wide. The ditch was 25 cm deep (from the
surface of the ridge to the bottom of ditch). Rice was planted on the ridges and fish
were stocked in the ditches. Rice plants were spaced at 17 cm x 13 cm, with
4-5 plant per clump and three line of rice plants per ridge. The ridges and ditches
were estimated to cover 84% and 16% of the field area, respectively. There were
three replicates for each of three different treatments. Treatments were randomly
arranged. Nine small (0.02 ha) experimental areas were established. The total
experimental field was 0.18 ha, and there was a 0.04-ha protective area around the
field. The different treatments were separated by a low bank that was covered with
a 50-cm plastic membrane that prevented fish escape and leakage of fertilizer.
Carp (7500 fry/ha) and grass carp (450 fry/ha) were released immediately after the
rice seedlings were transplanted. Supplemental feed (375-390 kg/ha) was given
until the rice plants bloomed. Fertilization and management techniques were the
same as used for ordinary ricefields.
Results and Discussion
Fertilization of Ricefield
When the ricefield was stocked with fish, the nitrogen, phosphorus, and potassium
(NPK) contents of the soil and water were increased significantly. Total nitrogen
was particularly high. Weeds and plankton in the ricefield normally compete with
rice for fertilizer. However, they were eaten by the fish and converted to a
55
Guangxi Agricultural Institute, Nanning, Guangxi Zhuang Autonomous
Region.
56
Guangxi Institute for Prevention and Cure of Parasitic Diseases, Nanning,
Guangxi Zhuang Autonomous Region.
210
RICE-FISH CULTURE IN CHINA
fertilizer that could be used by the rice. The physical and chemical properties of
the soil also became more suitable for growth and development of the rice.
Oxidation and Reduction Potential of the Soil
A rice-fish ecosystem benefits both crops. Fish movements in the shallow water
break the surface membrane formed by the microorganisms covering the soil. This
increases the dissolved oxygen level in the soil and elevates its oxidation and
reduction potential during the period of rice growth. These changes improve the
oxygen content and effectively increase the utilization rate of soil nutrients. The
ridge-ditch system allows water to be drawn into the soil in the ridge without
having a negative impact on the fish. The sun can also increase the temperature of
cultivation layer, which helps increase rice yields, especially of late rice. The
ridge-ditch system can allows for the use of direct seedling, ratooning, and zerocultivation method of rice planting.
NPK Content of Rice Plants
The NPK contents of the leaves and culm of rice plants grown with fish were
higher than in the control. These differences were correlated to the differences in
NPK levels in the soils in the two plots.
Chlorophyll Content of Plants
The chlorophyll content of rice plants at every developmental stages were
significantly higher in the experimental ricefield. The high chlorophyll content
indicates that the process of photosynthesis was more efficiency, which would lead
to the accumulation of more carbohydrates.
Surface Area of Leaves
The surface area of leaves has higher in the early developmental stages in the
experimental ricefield. In the booting and mature stages the factors were 6.9 and
2.5, respectively. In the control fields, the corresponding figures were 5.6 and 1.4.
The larger surface area of the leaves and the higher content of chlorophyll will
increase the efficiency of photosynthesis, and therefore increase the number of
effective ears, the number of grains per ear, and the weight of the grains.
Activity of the Root System
The activity of the root system is expressed by the volume of water that flows
through a wounded stem per unit of time. Strong activity means that the root
system can absorb more nutrients from the soil. The root systems of rice plants
grown in the experimental field always had stronger activity than the roots of plants
in the control field at all developmental stages.
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211
Accumulation of Dry Matter
The NPK content, surface area of the leaves, chlorophyll content, and activity of
the root system were all higher in the rice-fish system. These differences are also
expressed in the accumulation of dry matter. The total dry weight of the whole rice
plant in experimental ricefield was 17.1 % higher than in the control field. This is
a fundamental condition for an increase in rice production.
Effect on Tillering
Tillering of the rice plant during the early stages of development is crucial stage
to the production of effective ears. The number of ears and the time of earing are
closely related to fertilizer level. The rice plants grown in the experimental field
had a greater rate of tillering per day and more effective ears per plant. Although
both fields originally received the same amount of fertilizer, the fish in the
experimental field promoted more efficient use and distribution of NPK. The fish
reduced the loss of fertilizer and increased soil fertility.
Weeds Growth
Carp are omnivorous and grass carp are herbivorous. However, grass carp
fingerlings also eat aquatic insects. When these two species of fish are stocked
together, weeds are can be controlled in the ricefield. In the experimental field,
there were significantly fewer weeds throughout the growing period.
Economic Benefits
The rice-fish system creates a mutually beneficial ecosystem. In the ridge-ditch
system, the production of fish can reach 642 kg/ha. At the same time, the fish add
fertilizer and eliminate pests and weeds from the ricefield. Rice yields were
increased by 14.4%. It has been estimated that the ridge-ditch system can double
total earnings.
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The Role of Fish in Controlling Mosquitoes in Ricefields
Wu Neng, Liao Guohou, Lou Yulin, and Zhong Gemei57
Starting in 1983, investigations were made for 5 years on the effect of controlling
mosquitoes after rearing fish in ricefields. In 1987, further financial support was
obtained and the research began to have economic impact.
Experiment Sites
The test site was in Quangzhou County in northeast Guangxi. More than 26 700 ha
of ricefields were suitable for fish culture (about 80% of the total cultivated land).
Traditionally, farmers stock 6000-9 000 common carp and 150-1500 grass carp
per hectare of ricefield after the rice is transplanted. No additional feed or
management was used, and fish yields were about 150 kg/ha. However, because
weeds were decreased and rice yields were increased, this type of cropping system
has expanded. By 1987, rice-fish culture was practiced on half of the ricefields that
were suitable for fish-rearing.
An isolated village in Quangzhou County was selected as an experimental site to
study changes in mosquito population density in ricefields. The village had 127 ha
of ricefields, and 90% of these fields were used for fish. The fish fmgerlings were
stocked into middle-rice fields after the rice seedlings were transplanted. When rice
was harvested, the fish had grown to about 100 g and could be used as food or
grown longer in the pond.
Methods
Mosquito Density in Ricefields
The main species of mosquitoes in the district are Anopheles sinensis, the main
vector of local malaria, and Culex tritaeniorhynchus, the vector of Japanese
encephalitis. Density measurements were taken once a week for a month before
and after the fish were stocked. Larva and adult mosquitoes were also examined
in a control village with no fish.
Frequency of Mosquito Biting
Mosquitoes were attracted to a special mosquito net 0.5 h after sunset in the fields
adjacent to both the experimental village and the control village.
57
Guangxi Institute for Prevention and Cure of Parasitic Diseases, Nanning,
Guangxi Zhuang Autonomous Region.
214
RICE-FISH CULTURE IN CHINA
Table 1. The relationship between the annual incidence of malaria and the area of
rice-fish culture in Quangzhou County.
Annual Incidence of
Malaria (1:100 000)
Rice-Fish Area
to Total Rice Area
(%)
Quangzhou
Entire
District
1978
0
11.6
6.6
1979
11
4.7
8.7
1980
25
2.4
23.7
1981
29
0.5
34.3
1982
35
0.6
35.4
1983
35
0.5
22.6
1984
34
0.4
14.0
1985
34
0.1
6.9
1986
43
0.1
6.5
1987
43
Ol
7.0
Age-Class Distribution of Larva (Pupa)
Larva numbers of each age-class were recorded throughout the year at both the
experimental site and the control site. The distribution of mosquitoes in each ageclass was evaluated and the differences were calculated.
Incidence of Malaria
The spread of fish culture in ricefields over the past 10 years in Quangzhou County
was traced. The incidence of endogenous malaria was recorded over the same
period and compared with the whole district.
Results and Discussion
Density of Mosquitoes
Compared with the control, the density of larva and adult mosquitoes was
remarkably lower when the fish were reared in the ricefields. A comparison of the
frequency of mosquito biting in the two locations also showed that contact between
humans and mosquitoes was greatly reduced in the village where a large area of the
ricefields was used for fish culture.
Natural mortality of mosquito larva is density dependent. The degree of the effect
depends on the stage at which mortality occurs. If natural predators consume
INTERACTIONS
215
mosquitoes during the early stages of growth, increased survival is likely to make
up for early losses. If mortality takes place in later stages, it is impossible to make
up for the loss. This will greatly affect the density of adult mosquitoes. In the
fish-rice field, the ratio of old larva and pupa was much lower than in the control
field. This suggests that because the fish feed on old larva and pupa, densitydependent survival has no effect. Therefore, it is reasonable to suggest that fish are
an effective biological control method for mosquitoes.
Incidence of Malaria
One of the most important criteria for judging the control of mosquitoes is the
incidence of diseases spread by the mosquitoes. Table 1 shows the increased area
of rice-fish fields in Quangzhou County and the annual incidence of endogenous
malaria within the county and within the whole district. As the area of rice-fish
culture has increased in Quangzhou County, the annual incidence of malaria has
decreased (correlation coefficient -0.9225). Although other measures were taken
to prevent malaria in Quangzhou County (e.g., inspection and control of sources
of infection), the relative number of cases was much lower than in other counties
in the district.
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A Comparative Study of the Ability of Fish to Catch
Mosquito Larva
Wang Jianguo and Ni Dashu,58
More than 100 species of fish eat mosquito larva, and many authors have suggested
species that are good at eating mosquito larva. In 1959, Chen Jiangxing and Gao
Kai achieved good results using common carp fry (Cyprinus carpio), and in 1979,
the Antiepidemic Station of Chengdu City, Sichuan Province, used silver crucian
carp (Carassius auratus) and grass carp (Ctenopharyngodon idella) to eliminate
mosquito larva. In 1976, the Antimalaria Group of Henan Province reported good
results when fish were raised in ricefields to control mosquitoes. Although
Dambusia qffinis, Panchax panchax, Mocropodes apercularis, and Pseudorasbora
parva are good for mosquito control, they are difficult to breed and there is a
limited supply of fry. In addition, these fish species are of little economic value
and are difficult to popularize.
There have been no reports on the ability of such fish as grass carp, silver common
carp (first generation of crosses between red carp and silver crucian carp), and nile
tilapia (Oreochromis niloticus) to eat mosquito larva. Earlier indoor experiments
reported by the World Health Organization were mostly conducted with fish that
were starved for 1-2 days before the mosquito larva were introduced.
A comparative experiment was carried out to determine the differences between the
amount of food taken by starved fish and by those reared in natural conditions.
Three common types of fish raised in ricefields were studied. The density of
mosquito larva in one midseason ricefield and two late ricefields where grass carp
were reared was also measured.
Materials and Methods
The research was conducted both indoors and in the field. The experiment on the
feeding rate was done indoors under controlled conditions. Fish of different sizes
were raised separately in a white round drum (40 cm in diameter, 20 cm of water).
To test the food intake of hungry fish, the fish was starved for 24 h after they had
adapted to their new environment. To test the food intake of fish under natural
conditions, the feed most liked by fish was added after the fish had adapted to their
new environment. Mosquito larva were added in batches. The amount of feed
added or unconsumed, and the number of mosquito larva of different ages eaten
by the fish, were recorded.
58
Institute of Hydrobiology, Academia Sinica, Wuhan, Hubei Province.
218
RICE-FISH CULTURE IN CHINA
The survey of the density of mosquito larva in ricefields with and without fish was
carried out by collecting water samples with a 500 ml aluminium ladle. If water
depth in the ricefields is assumed to be 6 cm, every hectare of ricefield stores
600 m3 of water, which is equal to 1200000 of the ladles used to collect samples.
A sample consisted of 150 ladles of water collected along the banks of a field. The
mosquito larva were separated from the water using a glass pipette and fixed in a
bakelite-capped tube that contained 30% alcohol. The larva were counted according
to three categories: Anopheles sinensis, Culex spp., and others. Between July and
August 1984, four samples were collected once every 2 weeks from the middle
ricefield. In 1985, the survey on a large area of two seasons of late rice was
conducted.
The survey of the mosquito larva density in the middle ricefield was conducted in
the Lianhu Fish Farm, Mianyang County, Hubei Province. The farm had 57.7 ha
of intensive fish-farming ponds and 31.7 ha of ricefields in continuous blocks. The
ricefields were surrounded by 1.6 ha of ditches. The ricefields were divided into
four blocks and managed by four different fish-farming teams. The area of the four
blocks of ricefields was 1.8 ha and the three fields were about 7.8 ha each. The
adjacent 5.3 ha of ricefields in which fish were not raised were used as the control
field. The strains of rice in the fields were different, but all were middle rice (the
distance between rows and plants was 13 cm x 20 cm). Tillage was not done in
ricefields in which fish were raised. No fertilizer was applied, and pesticides were
used only when necessary.
On 18 April 1984, sodium pentachlorophenate was used to eliminate weed, fish,
and leeches from the ricefields, and fry were raised in the 0.8 ha of straight ditches
around the four blocks of ricefields. On 19 May, 1.1 million grass carp fry were
introduced. On 23 June, 2.6 million summer grass carp fingerlings were collected.
In late June, 390 000 summer grass carp fingerling and 30 000 silver crucian carp
fingerlings were released into the rice paddies (average 13230/ha or 1-2/m2). In
ricefields with fish, fish ditches were dug. No feed was put into the ricefields. The
surveys of the density of mosquito larva in the two seasons of late rice where grass
carp was raised and in the control fields were conducted on 10 ha in Chongyang
County, Hubei Province.
Results
The food intake of hungry fish and fish under natural conditions were quite
different. The number of mosquito larva eaten by grass carp under natural
conditions was 73.4% of the intake when the fish were hungry (Table 1). Silver
crucian carp consumed 36.3% under natural conditions compared with hungry
conditions (Table 2). The number of mosquito larva consumed by nile tilapia under
natural conditions was only 32.5% of that under hungry conditions (Table 3). Nile
tilapia showed the greatest differences in intake under the two conditions, followed
by silver crucian carp and grass carp. In the indoor experiment, grass carp almost
always preferred mosquito larva to duckweed when they were fed together. This
may explain why grass carp normally eat more mosquito larva than the other two
species. Tables 2 and 3 show that when feed is given, the silver crucian carp and
219
INTERACTIONS
Table 1. Intake of mosquito larva by grass carp when hungry (H) and
under normal feeding (NF) conditions.
Fish
Feed in 24 h
Intake in 24 h
Intake of
Larva Duckweed Each Fish
(No.)
(g)
(No.)
No.
Size
(cm)
Larva
(No.)
Duckweed
(g)
NF
10
4.7
3650
50
2360
9.0
236
H
10 4.1-5.2
4000
-
3130
-
313
NF
10
3500
50
3363
8.5
336
H
10 4.1-5.2
4800
-
4670
-
467
4.7
Ratio of
Normal to
Hungry
Feeding
(%)
75.4
72.0
Table 2. Intake of mosquito larva by silver crucian carp when hungry (H)
and under normal feeding (NF) conditions.
Feed in 24 h
Fish
Intake in 24 h
No.
Size
(cm)
Larva
(No.)
Fish
Powder
(g)
Larva
(No.)
Fish
Powder
(g)
Intake of Ratio of Normal to
Each Fish Hungry Feeding
(No.)
(%)
NF
10
5.0
3000
14
742
11.5
72
H
10
5.0
4000
-
2016
2
202
NF
9
5.0
2350
10
1290
2
143
H
9
5.0
4000
-
3575
-
397
36.8
36.1
nile tilapia eat more fish powder than mosquito larva. The intake of mosquito larva
is not correlated with increased body size (Tables 1-3). In both groups, grass carp
eat the greatest number of mosquito larva, followed by silver crucian carp and nile
tilapia.
The number of Culex spp. larvae consumed can be determined by counting the
respiratory ducts that survive digestion intact. During the experiment, of the
300 Culex larva fed to the fish, only 261 respiratory ducts were recovered (253
from fish excrement and 8 from the sediment). This is only 87% of the number
consumed. This suggests that when the number of mosquito larva consumed by fish
is assessed, the number should be corrected by 13%.
220
RICE-FISH CULTURE IN CHINA
Table 3. Intake of mosquito larva by nile tilapia when hungry (H)
and under normal feeding (NF) conditions.
Feed in 24 h
Fish
Size
(cm)
No.
Intake in 24 h
Larva
(No.)
Fish
Powder"
(g)
Larva
(No.)
Fish
Powder
(g)
Intake of
Each Fish
(No.)
79
NF
10 4.4-6.0
2000
-
790
2.05
H
10 4.4-6.0
5000
-
2802
-
NF
10 4.4-6.0
1500
-
1002
1.85
H
10 4.4-6.0
3800
-
2709
-
Ratio of
Normal to
Hungry
Feeding
(%)
280
28.2
100
271
37.0
* Figures missing in original Chinese publication.
Table 4. Mosquito larva density in middle ricefields with and without fish culture.
Anopheles spp.
(No./ha
xlOOO)
Middlerice
Date
Culex spp.
(No./ha
x 1 OOP)
Others
(No./ha
x 1 OOP)
Total
(No./ha
x 1 OOP)
12 July 1984 With fish 8 II. 8 II. 8 24
Without fish 24 II.III.VI
16
II-.III.
0
40
25 July 1984 With fish 8 II. 0 0 8
Without fish 16 II.III.
12
Aug
1984
Without
24 Aug 1984
fish
With
8
II.
With f i s h 0
Without fish 16 II.II.
0
8
fish
0
24
0
88
16 II.II.
16
40
0
8
8
0
24
8
III.
Average With fish 4 2 6 12
Without
fish
16
10
6
32
The field surveys of the middle ricefields in Mianyang County (Table 4) show an
average of 32000 larvae when no fish were present, and one-third of that number
when fish were present. The fields without fish had four times the number of
Anopheles sinensis and five times the number of Culex spp., but the same number
of other mosquito larvae. In a more extensive survey in Chongyang County, the
221
INTERACTIONS
Table 5. Density of mosquito larva in two seasons of late ricefields with
and without fish culture, Chongyang County.
Anopheles
spp.
Culexspp.
(No./ha
(No./ha
x 1 OOP) x 1 OOP)
Others
(No./ha
x 1 OOP)
Total
(No./ha
x 1 OOP)
Location
Ricefields
Agro-Science Institute
Rice-fish
culture
0
Xiexing village, Taishan
township
Rice-fish
culture
0
Xiaxing village, Shaping
district
Rice-fish
culture
Wugang village, Shaping
district
Rice-fish
culture
0
Bailuo village group 6,
Rice-fish
Guikou township culture
0
Bailuo village group 9,
Rice-fish
Guikou township culture
0
Nanlin village, Qingshan
town
Rice-fish
culture
0
Taiping village, Huaqi
township
Rice-fish
culture
0
Lukou village group 9,
Rice-fish
Lukou town culture
0
Bailuo village, Shaping
district
8IV
Without fish 961. V.
24II
8
81.
128
Nanlin village, Qingshan Without fish 16II.IV 24 IV.II.II 40
town
Lukou village group 9,
Lukou town
Average
Without fish 16 II.IV
Rice-fish
culture
Without
fish
16 H.HI
32
0
0.9
0
0.9
37.3
13.3
16
66.6
fields with grass carp had 900 larvae per hectare compared with 66 700 in the fields
without fish (a difference of 99%, see Table 5). In this area, only one field with
fish had any mosquito larva. This field monitoring clearly shows that grass carp
can eliminate large numbers of mosquito larvae from ricefields.
222
RICE-FISH CULTURE IN CHINA
Discussion
Grass carp more effectively eliminate weeds and mosquito vectors in the ricefield
than silver crucian carp and nile tilapia. Their body shape also seems to be better
adapted to the shallow water in ricefields. Grass carp also have a higher economic
return. When the excrement of grass carp that have eaten mosquito larva was
examined, only the respiratory ducts were found entirely intact. Although the head
of the mosquito larva is shell-like, it was ground to pieces and could not be
counted. However, Anopheles spp. do not have respiratory ducts and this method
of computation requires further discussion.
According to a report by Yi Mengjie and his colleagues in 1984, a 4.9-cm grass
carp can catch 141 mosquito larva per night. In our experiments, each night grass
carp the same size could catch 236 mosquito larva, which weighed 8.3 g (100II-IV
stage larva weighed 3.5 g).
Generally, the peak period for mosquito larva in ricefields is between late August
and early September. Because of the field work needed for watering and
harvesting, our survey continued only until late August when there was no peak
and mosquito density was not high.
Summary
There are differences among the three species of fish in their food intake. The
number of mosquito larva eaten under normal conditions is lower than when the
fish are hungry. When the fish are the same size, grass carp eat the most larva,
followed by silver crucian carp and nile tilapia. Fish reared in ricefields can
eliminate up to 99% of the mosquito larva, Based on the indoor experiments, 100%
of the mosquito larva in the ricefield could be eaten and this would still not fully
satisfy the food requirements of the fish. Based on our experiments, grass carp
would be the best species to control mosquitoes in ricefields.
Ability of Fish to Control Rice Diseases, Pests, and Weeds
Yu Shut Yon,59 Wu Wen Shang,59 Wei Hal Fu,60 Ke Dao An,™ Xu Jian
Rang,61 and Wu Quing Thai62
From 1985 to 1987, a series of tests on rice-fish culture were conducted in
Shangyu, Xiaoshan and Huangyan Counties, Zhejiang Province, to determine if
grass carp, common caip, and nile tilapia could be used as biological control agents
in ricefields.
Material and Method
Field Arrangements
A suitable ricefield was selected as the test plot. Before the field was ploughed, the
border dikes were raised to 40 cm, and earth dams were built to separate the
different test plots. Space for fish ditches and pits was left when the seedling were
transplanted. After the rice was transplanted, fish ditches and pits were dug and a
fish screen was installed at the outlet.
Selection of Fry and Breeding Fish
Fry that had a body length of 3-4 cm and were able to swim against the current
were selected. Healthy, strong fish with shining body colour, no injuries, and a
body weight of 20-50 g were chosen as breeding fish.
Rice Cultivation
Fish were stocked in the test plot 7 days after the early rice was transplanted. The
fish were moved into the fish ponds before the early rice was harvested and
returned to the test plot after the late rice was transplanted. Fish were harvested
just before the late rice was harvested. In the test plot, water was kept at a depth
of about 10 cm, and basal fertilizers and top dressing were used. No pesticides,
seed treatments, or herbicides were used.
59
Agricultural Department of Zhejiang Province, Hangzhou, Zhejiang
Province.
60
Agricultural Bureau of Shangyu County, Shangyu, Zhejiang Province.
61
Agricultural Bureau of Huangyuan County, Huangyuan, Zhejiang
Province.
62
Agricultural Bureau of Xiaoshan County, Xiaoshan, Zhejiang Province.
224
RICE-FISH CULTURE IN CHINA
Fish-Farming Treatments
Six different treatments were carried out in Shangyu County in 1986, and each
treatment was repeated three times. The treatments were: (1) grass carp (5 250/ha),
(2) common carp (5 250/ha), (3) nile tilapia (5 250/ha), (4) grass carp (600/ha) and
common carp (3 000/ha) together, (5) long-term deep-watering for fish-farming,
and (6) normal water irrigation for fish-farming. In 1987, three different species
of fish (grass carp, common carp, and nile tilapia) were raised. For polyculture,
1500 fish of each species were used per hectare. For pure cultures 4 500 fish were
raised per hectare. The control plot was the same as in 1986. No comparisons
between fish and no-fish plots were made in Xiaoshan and Huangyan.
Survey Methods
Twenty clumps in the small plots and 50-100 clumps in the large plots were
inspected for rice planthoppers, 500 clumps were examined for rice borer,
40 clumps in the small plots and 100 clumps in the large plots were examined for
rice leafrollers, and 50 clumps in the small plots and 200 clumps in the large plots
were examined for rice sheath and culm blight. Weeds were sampled at five
locations (0.11 m2 each) in the ricefield, and records were kept of variety and fresh
weight.
Results and Analysis
Control of Diseases, Pests, and Weeds
Control of rice planthoppers. The raising of fry in early ricefields
provided poor control of rice planthoppers; however, raising breeding fish
provided good control. As the fish grew in size during the growing period of late
rice, they provided good control of rice planthoppers. A survey on 10 July 1985
in Xiaoshan showed that there were 1900 rice planthoppers (third generation) per
100 clumps in early ricefields with fry, a decrease of 34.5% compared with
2900 rice planthoppers per 100 clumps in the early ricefield without fish. In
ricefields with breeding fish there were 1030 rice planthoppers per 100 clumps in
the early ricefields, a decrease of 64.5% compared with ricefields without fish. A
survey on 20 September 1985 indicated that there were 2410 rice planthoppers
(fifth generation) per 100 clumps in the late ricefield with fish, a decrease of
734.3% compared with fields without fish.
Different varieties of fish had different effects. Investigations from 1986 to 1987
at the test plot in Shangyu showed that there was a relatively large difference
(Table 1) in the control of rice planthoppers during the peak season. The ricefields
in which only grass carp were raised showed the best control of rice planthoppers.
The fifth and sixth generation planthoppers were decreased by 40.5% and 74.2%
in 1986 and by 57.3% and 59.4% in 1987, respectively, compared with the control
field. Polyculture of the three varieties of fish was less effective than pure cultures
of grass carp.
225
INTERACTIONS
Table 1. Effect of different treatments on the number of rice planthopper nymphs
per 100 clumps in late ricefields.
Fourth Generation
Treatment
Normal watering
field without fish
culture
3 Sept
1986
8 Sept
1987
233
548
Fifth Generation
23 Sept 26 Sept
1986
1987
1273
8228
Sixth Generation
12 Oct
1986
1147
26 Oct
1987
10390
Deepwater field 237 340b 1220 6123" 690b 8755*
without fish
culture
Deepwater field 190 215k 753* 3513k 290" 4220b
with grass carp
culture
Deepwater field 123b 260b 526b
456b 4750b
6728b
with common carp
culture
Deepwater field 53b 305b 840*
390" 5100"
6938b
with nile tilapia
culture
Deepwater field 167* 218b 567b
530" 4013"
4625"
with mixed-fish
farming
* Significant difference.
b
Highly significant difference.
There were several reasons that the fish could effectively control rice planthoppers.
First, the rice planthoppers normally oviposit on plant leaves near the bottom of
the plant. The grass carp consume these outer leaves, which controls hatching of
ova. Second, fish eat rice planthoppers that fall into the water, which directly
reduces the number of insects in the field. Third, the deep water protects parts of
the rice plant on which rice planthoppers oviposit and feed. In 1987, there was a
severe attack on late rice by the brown-back rice planthopper (Nilaparvata lugens).
Some plants were infected with sheath and culm blight in normal and deep-water
ricefields without fish; however, in the ricefields with fish, the rice plants
continued to have green stems late in the growing season, and the crop ripened
without the use of any pesticides. The plots with grass carp produced the highest
yields.
226
RICE-FISH CULTURE IN CHINA
Control of rice stem-borer. Observations in Shangyu from 1986 to 1987
indicated that there were, on average, 1980 rice borers per hectare in ricefields
with fish. This was a decrease of 51.1% compared with normal-water ricefield
without fish, and a decrease of 47.2 % compared with deep-water ricefield without
fish. A survey on 1 July 1987 showed that the attacked rate per plant was 0.7% in
ricefield with fish. This was a reduction of 44.3% compared with normal-water
ricefields without fish and a reduction of 27.7% compared with deep-water
ricefields.
There was a significant difference in the number of pests per hectare and the
attacked rate per plant over the 2-year period in ricefields with fish compared with
normal-water ricefields without fish. However, the differences were not significant
compared with deep-water ricefields without fish. Observations in Xiaoshan
showed that the attacked rate per plant was 0.7% in the ricefield with adult fish,
a decrease of 80.6% compared with ricefields without fish. The main reasons that
the fish were able to mitigate harm done by rice borer were that the pests were
eaten when they fell into the water. In addition, grass carp eat the rice borers when
they strip the lower leaves, which are often attacked by rice borers.
Control of rice leafrollers. A survey in Xiaoshan on 8 July 1986 showed
that there were 90.5 rice leafrollers (second generation) per 100 clumps in the
ricefields with fish. This was a 6.5-times increase compared with 12 rice leafrollers
in the ricefield without fish. The survey on 22 September 1987 indicated that there
were 15.4 rice leafrollers (fourth generation) per 100 clumps in the late ricefields
with fish, an increase of 1.9 times compared with the ricefields without fish. In
Shangyu, a survey on 10 September 1987 indicated that the highest number of
larva of rice leafroller (fourth generation) per 100 clumps was observed in the late
ricefields with grass carp. There were 234 larva with grass carp and 193 larva with
polyculture. This was an increase of 57.2% and 29.5%, respectively, compared
with the 149 larva in the control plot. The reasons that fish-farming increased the
number of rice leafrollers in the ricefields were that the fish did not eat the larvae.
As well, the great amount of fish waste, the tender, green rice plants, the deep
water in the field, and high humidity in the microclimate all favoured oviposition,
hatching, and feeding of larvae.
Control of rice sheath blight and clump blight. From 1986 to 1987 in
Shangyu, plant morbidity and disease incidence were reduced in the early ricefields
with fish. This was highly significant compared with normal-water ricefields
without fish, but there was no significant difference compared with the deep-water
control. Disease incidence declined by 9.9-19.6%. Plant morbidity in the late
ricefields with fish was 13%, a decrease of 58.4% compared with the normal-water
control and of 24.9% compared with the deep-water control (Table 2). There were
several reasons why damage from rice sheath blight and culm blight were
mitigated. First, the fish (mainly grass carp) stripped the diseased leaves near the
bottom of the rice plant, which directly diminished sources for reinfection in the
field. Second, after the bottom leaves of plants were ripped off, the microclimate
in the field was unfavourable to infection because ventilation and light penetration
INTERACTIONS
227
Table 2. Index of disease incidence for rice sheath blight and culm blight in early
ricefields.
Plant Morbidity (%)
9 July 1986
20 July 1987
Disease Incidence Index
9 July 1986
20 July 1987
Normal watering field 22.2 34.0 7.2 13.5
without fish culture
Deepwater field without
fish culture
9.7"
22.2a
4.8a
8.1"
Deepwater field with
fish culture
8.9"
19.5a
4.T
7.3a
" Not significantly different.
were improved. Third, long-term deep-water conditions prevented germination of
the spores and reinfection.
Control of weeds. Fish control weeds grown in ricefields. Grass carp eat
21 different species of weeds in 16 families (e.g., Echinochloa crusgalli,
Eleocharis yokoscensis, Cyperus difformis, Rotala indica, Sagittaria pygmaea,
Monochria vaginalis, and Marsilea quadrifolia). In addition, common carp eat
young roots, buds, and underground stems of weeds in the ricefield. Observations
in late ricefields in Xiaoxhan in 1987 showed that there were three different kinds
of weeds in rice-fish fields without weeding. The fresh weight of the weeds was
117 kg/ha. This represented a decrease of one kind of weed and 29.7% in fresh
compared with ricefields with manual weeding, and a decrease of six kinds of
weeds and 97.2% in fresh weight compared with a ricefield without fish and
without weeding.
Only Echinochloa crusgalli, Paspalwn distichwn, and Alternanthera philoxeroides
survived in the rice-fish fields. Echinochloa crusgalli was transplanted in the field
with the rice seedlings and the fish were unable to control it effectively. Paspalum
distichum normally extended from border dikes into the ricefield. Young buds and
stems of Alternanthera philoxeroides were eaten by the fish, but they were not well
liked. The surface of the ricefields with fish was smooth and grass-free. Weed
control was more effective than with either manual weeding or the use of
herbicides.
Economic and Ecological Benefits
Economic benefits. In Shangyu in 1987, rice yields in both early and late
ricefields with fish reached 11093 kg/ha, an increase of 12.9% compared with the
control (9 821 kg/ha). With a fish yield of 600 kg/ha, the net increase in income
was CNY1986/ha. In Huangyan in 1986, early and late ricefields with fish
produced 11 334 kg/ha of rice and 1778 kg/ha of fish with a net income of
228
RICE-FISH CULTURE IN CHINA
CNY9230/ha. This was an increase of 25.7% in income compared with the
control. The practice of rice-fish farming has been popularized to 16650-20000
ha in Zhejiang Province, and to a total of over 135 000 ha throughout China.
Ecological benefits. The interactions of fish and rice create changes in the
ecology of the ricefield. The ricefields hold water all season because of the fish.
The movements of the fish stir the soil, which plays a role in weeding the field and
increases the dissolved oxygen content in the soil. Ventilation and light penetration
are also improved. The fish eat weeds, damaged plant leaves, and some pests. In
exchange, they discharge wastes that add organic manure to the ricefield.
Experiments have shown that 3 000 grass carp per hectare (6.3-11.2 cm in length)
discharge 1440 kg of waste in a month. Therefore, they contribute a constant
supply of fertilizer to the rice plants. Rice-fish fields require less farm chemicals.
This diminishes problems related to pollution and toxic residues and to some
extent, protects natural enemies of plant pests and increases their effectiveness for
biological control.
Issues and Discussions
Rice-fish farming still faces some problems. First, animals pests (e.g., rats and
snakes) eat fish in ricefields and frogs eat fry. Surveys in Shangyu in 1986
indicated that the harvest rates for grass carp, common carp, and nile tilapia were
78.9%, 82.1%, and 92.3%, respectively. Second, the fish do not control
Echinochloa crusgalli; therefore, herbicides were required. Third, large grass carp
stocked with late rice may damage the ricefield. Fourth, the proper ratio of fish
pits and fish ditches in the ricefield must be determined to achieve bumper harvests
for both rice and fish.
Distribution and Residue of Methamidophos in a
Rice-Azolla-Fish Ecosystem
v,. V^~.,. 64 _ M j ft.-.. r\~A,65
Xu Yinliang™63 Xu
Yong, and Chen Defii
Methamidophos (O,S-dimethyl phosphoramidothioate) is an organophosphorus
insecticide that is used in great quantities in ricefields in China. Rice-fish culture
is common in the southern parts of China as well as in many other rice-producing
countries (e.g., Thailand, Malaysia, and the Philippines). It is necessary to apply
pesticides to control rice pests in the rice-azolla-fish ecosystem. In this study, the
distribution, degradation, and residual behaviour of methamidophos were measured
in both simulated and natural rice-azolla-fish ecosystems.
Materials and Methods
Test Materials
Two rice varieties were used: Sifu 8512 (an early rice) and Xinshui 04 (a late rice).
The soil was a silty loam with a pH of 7.1 and an organic matter content of 1.3%.
The fish species used was nile tilapia (Oreochromis niloticus) that were 4-6 cm in
length, and the azolla was Azolla caroliniana.
A 50% methamidophos emulsion was obtained from the Hangzhou Pesticide
Factory. The Institute of Nuclear-Agricultural Sciences, Zhejiang Agricultural
University, synthesized the 35S-methamidophos (specific activity 5 227 dpm/mg,
radio chemical purity 99%). The 50% 35S-methamidophos emulsion was formulated
in 59% 35S-methamidophos, 47% methanol, and 3% emulsifier (PP2).
Trial Design
Simulated ecosystem. This part of the study was conducted under outdoor
conditions. A glass aquarium (95 cm x 68 cm x 45 cm) held the soil (200 kg), rice
plants (30 hills), fish (30), and azolla. Surface water was maintained at a depth of
about 7-10 cm.
63
Institute of Nuclear-Agricultural Sciences, Zhejiang Agricultural
University, Hangzhou, Zhejiang Province.
64
65
Institute for the Control of Agrochemicals, Hangzhou, Zhejiang Province.
Institute of Soil Sciences, Zhejiang Academy of Agricultural Sciences,
Hangzhou, Zhejiang Province.
230
RICE-FISH CULTURE IN CHINA
Table 1. Trial design to measure the residual behaviour of 35S-methamidophos ^S-M)
applied at a rate of 0.75 kg/ha in simulated and natural ecosystems of rice-azolla-fish.
Spraying Date,
Early Rice
16 26 20
June June Aug
Treatment
Sampling
Sampling
rj)ate>
Total
Date,
Late Rice
Pesticide
Early
30 30 14 Application
Rice
30 14
Aug Sept Oct
(kg/ha)
(7 July) Oct Nov
Spraying Date,
Late Rice
Simulated ecosystem
3 applications
—
x
x
—
x
—
2.25
x
x
—
5 applications
x
x
x
x
x
—
3.75
x
x
—
Dynamic
x
—
—
—
—
—
0.75
3 applications
—
x
—
x
—
x
2.25
x
—
x
5 applications
x
x
—
x
x
x
3.75
x
—
x
Timing of sampling
Natural ecosystem
Table 2. Extraction procedures using a tissue homogenizer for 2 minutes on a 5-g sample.
Sample
Azolla
Straw
Fish
Solvent (ml, per extraction)"
EA, 40
EA, 40
A:M (7:3,V/V), 30
Na2SO4 (anhydrous, g)
10
10
5
' EA ethyl acetate; A:M acetoneimethanol.
The trial was divided into two treatments. The first was one application on early
rice and two applications on late rice, the second was two applications on early rice
and three applications on late rice. The application rate was 0.75 kg/ha. The
interval between the latest application and harvest was 35 days for early rice and
30 days for late rice. Samples of water, soil, rice plants, azolla, and fish were
taken for analysis of 35S-methamidophos residue at different times. After the
harvest of early and late rice, the residues of 35S-methamidophos in different parts
of the ecosystem were analyzed.
Natural rice-azolla-fish ecosystem. The experiments were carried out in
experimental plots that were each 430 m2. The trial design was similar to the
simulated rice-azolla-fish ecosystem (Table 1). All treatments were replicated
three times.
INTERACTIONS
231
Sample Preparation and Measurements
Prior to fortification with 35S-methamidophos to give concentrations of either
0.5 or 0.1 ppm, plant tissues were macerated, soil was placed in Buchner funnels
and stripped of excess water by aspiration, and whole fish (one per sample) were
weighted and cut into small pieces.
Extraction and clean-up. Water samples (20 ml) were extracted with ethyl
acetate three times (30 ml, 20 ml, 20 ml). The Na2SO4 was added before the first
extraction. The straw, azolla, and fish extracts were filtered through a layer of
activated carbon (Celite 545, 1:4, WAV) in Buchner funnels. All the fractions from
the sample were combined in 250-ml round-bottom flasks, evaporated in rotary
evaporator, and subjected to radioanalysis (Table 2).
The soil (5 g) was extracted with water and methanol (3:1, V/V, 40 ml). The
extract was filtered through a glass funnel. The crude extract (equivalent to 2.5 g
of soil) was analyzed following the analytical method used for the water. Husk and
brown rice (10 g) were also extracted with methanol and ethyl acetate (1:4, V/V,
50 ml) using the method of vibrating extraction. Extract, equivalent to 5 g of husk
or brown rice, was evaporated in a rotary evaporator and subjected to
radioanalysis.
Radioanalysis. The radioactivity in the organosoluble fractions from
extraction of the water, soil, straw, fish, azolla, husks, and brown rice was directly
determined using a liquid scintillation counter (Model LKB-1217). Recoveries of
35
S-methamidophos from the seven substrates are listed in Table 3.
Gas chromatography analysis. The residues of methamidophos in the
samples from the field trial were detected by gas chromatography (GC) using
AFID (alkali flame ionization detection). The operation parameters were: gas
chromatography Perkin-Elmer Sigma 2000, column 120 cm x 2 mm ID, 2%
Reoplex 400 on the gas chromQ, air 18 psi, H2 18 psi, N2 42 ml/min, column
temperature 170°C, and inlet and outlet temperature 210°C. Quantification of
methamidophos was based on the average peak heights of external standards that
were injected before and after sample analysis. The GC recoveries of
methamidophos from the seven substrates are listed in Table 4.
Residue in the simulated rice-azolla-fish ecosystem. After application of 50%
35
S-methamidophos emulsion to the rice plants in the rice-azolla-fish ecosystem at
the rate of 0.75 kg/ha, samples of water, soil, straw, azolla, and fish were taken
for analysis of methamidophos residue at different times from immediately after
application to 14 days. The dynamics of 35S-methamidophos residue are listed in
Table 5. The 35S-methamidophos disappeared exponentially from the simulated
rice-azolla-fish ecosystem.
232
RICE-FISH CULTURE IN CHINA
Table 3. The recovery and background of 35S-methamidophos (35S-M).
Sample
size
(g,ml)
Water
35
S-M Cone.
(mg) (ppm)
Counting
(x+s)dpm
CV Recovery
(%)
(%)
Background
(dpm)
20
2
0.1
1030.4±32.2
3.1
95.7
76.6
20
10
0.5
4837.1±74.5
1.5
92.5
76.6
10
1
0.1
318.6±30.9
9.7
88.9
97.0
10
5
0.5
1302.6±54.6
4.2
93.7
97.0
Azolla
10
1
0.1
495.2 ±31.2
6.3
93.6
62.8
Fish
5
0.5
0.1
210.6±12.6
6.0
87.3
102.6
Brown rice
10
1
0.1
270.2±5.6
2.0
90.4
66.3
Husk
10
1
0.1
279.3 ±15.4
5.5
88.3
80.2
Straw
5
0.5
0.1
309.4±11.2
3.6
94.6
91
Soil
Table 4. Gas chromatography (GC) recovery of 35S-methamidophos.
Item
Concentration
(ppm)
Recovery
(%)
CV
(%)
Water
0.1
95.6±1.3
1.5
0.5
103.0±3.1
3.2
0.1
82.5±4.6
5.6
0.5
81.3±3.8
4.7
Fish
Brown rice 0.1 83.6±4.0 4.8
Husk
0.1
82.4±3.3
4.6
0.5
86.2±2.7
3.4
Straw
5.0
78.4±2.9
3.5
Soil
0.1
87.1 ±3.5
4.0
Azolla
05
83.3±2.7
3.3
INTERACTIONS
233
Table 5. Dynamics of 35S-methamidophos residues (ppm).
Time Course (day)
0
0.25
1
3
5
9
14
0.132
0.164
0.303
0.259
0.184
0.072
0.013
Soil
nd"
nd
nd
nd
nd
nd
nd
Fish
0
0.187
0.606
0.328
-
0.178
0.127
Azolla
3.136
4.157
2.944
1.497
0.469
0.070
0.009
Straw
29.066
16.742
9.336
3.853
-
0.799
0.136
Water
" nd nondetectable.
Table 6. Residues of 35S-methamidophos in the simulated ecosystem (ppm).
No. of
Treatments
Water
Soil
Azolla
Fish
Straw
Husk
Brown
Rice
1
0.002
nda
nd
0.412
0.008
0.011
0.010
2
0.004
nd
nd
0.552
0.036
0.034
0.010
Early rice
Late rice 2 Trace nd nd 0.212 0.006 0.176 0.014
3
Trace
nd
nd
0.400
0.122
0.346
0.043
a
nd nondetectable.
Table 7. Effect of polishing on concentration of 35S-methamidophos in brown rice.
Weight Concentration
(g)
(ppm)
Quantity
(mg)
Ratio
(%)
Total
Quantity
(mg)
Clearance
Rate
(%)
Polished rice
17.5
0.005
0.0875
41.2
0.2125'
5CT
Bran
2.5
0.050
0.1250
58.8
-
-
* Value for polished rice plus bran.
After 1 day of equilibrium, the residues of 35S-methamidophos in the azolla, water,
and fish reached a peak (4.16, 0.30, and 0.61 ppm, respectively) then decreased
exponentially. The half-lives of 35S-methamidophos in azolla, water, and fish were
1.5, 2.8, and 6.2 days, respectively. The half-life of 35S-methamidophos in the
straw was 2.2 days. There was no residue detected in the soil.
234
RICE-FISH CULTURE IN CHINA
Residue in the simulated rice-azolla-fish ecosystem. The 35Smethamidophos was applied to the early and late rice in the simulated ecosystem.
The residues of 35S-methamidophos in the different parts of the ecosystem at
harvest are listed in Table 6.
The interval between the last application and harvest was 35 days for early rice and
30 days for late rice. At harvest of early and late rice, there were trace residues of
35
S-methamidophos in the water, but no residues in the soil of the azolla. The
residues of 35S-methamidophos in fish were 0.41-0.55 ppm when harvested with
early rice and 0.21-0.40 ppm when harvested with late rice. This decrease of
concentration was related to the increase in the weight of the fish.
The distributions 35S-methamidophos residue in the parts of the rice plant differed.
The residue was highest in the husk and lowest in the brown rice (e.g., for late rice
the concentrations were 0.35 ppm in the husk, 0.12 ppm in the straw, and 0.04
ppm in the brown rice). With increases in application times, the concentrations of
35
S-methamidophos residues in the rice plant increased. For example, in husks of
early rice, the residue was 0.01 ppm for one application and 0.03 ppm for two
applications. However, there was no linear correlation to the increase.
In the natural rice-azolla-fish ecosystem, there was only 0.09-0.10 ppm of
methamidophos residue in the rice husks when the early rice was harvested. In the
other parts of the ecosystem, no residues were detected.
Influence of polishing brown rice. Brown rice (20 g) that had a residue
of 0.01 ppm was polished for 10 minutes. The residue of methamidophos in
polished rice was decreased to 0.005 ppm (Table 7).
Residue in fish. When applied twice to early rice and three times to late
rice, the distribution and residue of 35S-methamidophos in fish when late rice was
harvested were determined (Table 8). The residue was highest in the viscera and
lowest in the scales. The edible portion of the fish body contained 26.9% of the
radioactivity and the nonedible portion contained 73.1 %.
Conclusion
Methamidophos is not well degraded by animals and plants. In female houseflies
with different doses of 32P-methamidophos, the parent compound has only been
detected in the extract of the houseflies, not in their metabolites or degradation
products. Experiments with white mice and houseflies have also suggested that the
metabolic pathway of methamidophos may be through the release of CO2.
However, the quantity of this metabolic product may be so low that it cannot be
detected. When extracts from rice plants and fish were made, separated on thinlayer chromatography, and scanned with a radioscanner, only the parent compound
was detected.
INTERACTIONS
235
Table 8. Distribution of 35S-methamidophos in different parts offish.
Weight
(g)
Concentration
(ppm)
Quantity
(mg)
Ratio
(%)
Head
7.320
0.525
3.843
38.22
Flesh
10.568
0.256
2.706
26.91
Viscera
2.536
0.775
1.965
19.54
Gill
1.152
0.543
0.626
6.22
Bone
2.136
0.291
0.622
6.18
Fin
0.841
0.243
0.204
2.03
Scale
0.587
0.154
0.090
0.90
Full fish 25.139 0.400 10.056 100.00
These experiments with the rice-azolla-fish ecosystem have demonstrate that:
•
•
•
•
The disappearance of methamidophos in the rice-azolla-fish
ecosystem was exponential. The half-lives of 35S-methamidophos in
azolla, water, fish, and straw were 1.5, 2.8, 6.2, and 2.2 days,
respectively.
When 2 x 0.75 kg/ha of 35S-methamidophos emulsion were sprayed
on early rice there was 0.01 ppm of methamidophos in the brown
rice and 0.55 ppm in the fish. When sprayed at 3 x 0.75 kg/ha on
late rice, there were 0.04 ppm in the brown rice and 0.40 ppm in
the fish.
When brown rice was polished the concentration of methamidophos
residue was reduced by about 50%.
Methamidophos is not well degraded by animals and plants. No
metabolic and degradation products were detected in the extracts
from rice plants and fish.
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Residue and Application of Fenitrothion in a Rice-Fish
Culture System
Lou Genlin,66 Zhang Thongjw,66 Wu Gan,66 Gao Jin,66 Shen Yuejuan67
Xie Zewan,67 and Deng Hongbing67
Fenitrothion (o,o-dimethyl-o-3-methyl-4-nitrobenzene phosphnothiocester) has low
mamalian toxicity (white rat oral LC^ 490-700 g/kg) and effectively controls stem
borers. Fenitrothion is one of twelve pesticides recommended by the Chinese
government for priority research and increased production. Pest and disease control
is one of the most important measures in rice production. Rice-fish culture is a
major component of freshwater fisheries. Pesticides with high efficacy and low
residual effects are needed to integrate production and increase yields of both rice
and fish. The effects of fenitrothion in rice-fish culture was studied in Sichuan
Province from 1984 to 1987.
Test Design
Fenitrothion Residue in Ricefields
Five 30-m2 treatment plots were designed to study degradation. Every treatment
was divided into subplots with three replicates. Water depth was maintained at
6.6 cm during the experiment. Samples were taken at 2 h, and 1,3,5, and 7 days
after application of 750 g/ha (50% EC 800 dilution). The residual experiment
(Table 1) included: using different dosages in ricefields (750-1125 g/ha, 50% EC
500-800 dilution), spraying the pesticide at different times, and multiple
applications of fenitrothion.
Fenitrothion Residue in Fish
The designs and treatments were identical to those used to study the effects in
ricefields, but the sampling interval was from 2 to 148 h at regular intervals after
application of the pesticide. Tests on residue distribution were made in tanks (50 L)
of clean oxygenated water.
Each tank contained 200 fish that weighed approximately 0.5 g. The range of test
concentrations was 0.05-2 ppm. Samples from internal organs were taken at
regular intervals. Benzene was used to extract residual pesticide from the rice and
66
Institute of Plant Protection, Sichuan Academy of Agricultural Sciences,
Chengdu, Sichuan Province.
67
Sichuan Provincial Bureau of Fisheries, Chengdu, Sichuan Province.
238
RICE-FISH CULTURE IN CHINA
Table 1. Design of residual test on rice.
Concentration
Number
of Times
50% EC 750 g/ha
50% EC 1125 g/ha
Time to Harvest (days)
1
28
1
21
1
14
2
35
28
2
28
21
2
21
14
3
35
28
21
3
28
21
14
3
35
28
21
3
28
21
14
fish. Dichlromethane and trichloromethane were used to extract residues from the
soil and water.
Results and Discussion
Degradation of Fenitrothion in Aquatic Ecosystems
Tables 2-4 indicate the degradation rate (%) of fenitrothion in rice and in the
environment. Fenitrothion broken down rapidly in rice. The degradation rate was
up 50% when used at 750-1125 g/ha (50% EC 500-800 dilution). The residue of
fenitrothion in rice was generally less than 0.1 ppm 5 days after application. Straw
and rice bran contained less than 25% after only 1 day. Over 90% of the
fenitrothion had been broken down after 7 days (Table 2). The residual curve
formula was:
yrice
= 2.8573 e03510x
which indicates that the half-life (HLy) in rice was 2 days. The rate of degradation
was also fast in soils and water under similar conditions (Tables 3 and 4). The
residue curve formulae were:
y^ = 2.9404 e03470* and
yw.ter = 2.7897 e-0-6053*
INTERACTIONS
239
Table 2. Degradation of fenitrothion in rice (ppm).
Test
Year
Time After
Spraying
(days)
Ra
D
R
D
R
D
0.08
0.441
-
9.690
-
6.878
-
1
0.222
49.66
2.309
76.17
1.613
76.55
3
0.140
68.25
1.428
85.26
0.983
85.71
5
0.066
85.00
0.571
94.11
0.388
94.36
7
0.024
94.56
0.221
97.72
0.222
96.77
0.08
0.390
-
7.860
-
6.914
-
1
0.171
56.15
1.948
75.22
2.263
67.27
3
0.100
74.86
0.820
89.58
1.021
85.23
5
0.066
83.08
0.291
96.30
0.295
95.73
7
0.034
91.28
0.203
97.42
0.143
97.93
1984
1985
Rjce Grain
Rice Bran
Straw
" R residue; D degradation.
Table 3. Degradation of fenitrothion in soil of ricefield (ppm).
Interval After
Using Pesticide
(days)
1984
R^
&**
D
R
Average
D
D
0.08
0.313
1
0.264
15.65
0.248
13.80
0.256
14.78
3
0.155
50.48
0.124
58.62
0.140
54.55
5
0.050
84.03
0.058
80.00
0.054
82.02
7
0.03
90.41
0.029
90.00
0.030
90.21
9
0.015
95.21
0.015
94.83
0.015
95.03
* R residue; D degradation.
0.290
R
0.302
240
RICE-FISH CULTURE IN CHINA
Table 4. Degradation of fenitrothion in water in ricefield.
Interval After Using
Pesticide (days)
R(ppm)a
0
1
3
5
7
0.973
0.134
0.019
0.015
0.0098
-
86.23
98.05
98.46
98.99
D(%)
aR residue; D degradation.
Table 5. Residue of fenitrothion in rice, soil and water.
Number Days from
Dosage
of
Using to
(g/ha) Applications Harvest
750
1125
a
Residue (ppm)
Rice
Grain
Rice
Bran
Straw
Soil
Water
1
28
ND
0.016
0.024
ND
ND
1
21
Trace
0.042
0.038
ND
ND
1
14
0.016
0.144
0.021
ND
Trace
2
28
ND
0.044
0.032
ND
Trace
2
21
0.003
0.076
0.054
ND
0.00010
2
14
0.020
0.496
0.213
ND
0.00042
3
21
0.010
0.162
0.057
ND
0.00033
3
14
0.022
0.623
0.223
Trace
0.00051
3
21
0.016
0.212
0.131
Trace
0.00030
3
14
0.032
0.810
0.304
Trace
0.00058
ND = not detectable.
which indicated that the half-life in soil was 2 days and that the half-life in water
was 1 day.
Table 5 gives the residual levels of fenitrothion in various parts of the rice and in
the soil and water. There were differences between the different dosages, number
of applications and intervals.
There was little contamination of the rice when it was sprayed from one to three
times. Soil and water were not polluted under these conditions. Under similar
dosages and number of sprays, residual levels were higher when the rice was
sprayed closer to harvest time. The soil and water were not polluted at any
INTERACTIONS
241
frequency of spraying. There was more residue after application at 1125 g/ha than
at 750 g/ha under similar conditions.
Accumulation of Fenitrothion in Fish
The level of fenitrothion in the fish increased as the level decreased in the water.
The pesticide in the water was absorbed and concentrated by the fish (Table 6).
When the fish were treated with different concentrations of the pesticide, the
residual level of the pesticide in the fish increased as the amount of residue in the
water increased. However, the coefficient did not increase without limit. After a
certain concentration, the coefficient decreased. For example, when grass carp
were kept in 0.05 ppm and 0.1 ppm, the coefficients after 2 h were 12.6 and 17.3,
respectively. The coefficients increased to 38.3 and 61.4 after 8 h. When the
concentration of the pesticide was higher (1 ppm and 2 ppm), the residue in the
fish increased to 2.0 ppm and 3.2 ppm, but the coefficients were only 2.5 and 2.1.
When different fish species (Table 6) were exposed to the same concentration, the
residue levels were different. Different species of fish have different shapes and
feeding habits, fat contents, and distributions. In all species, fenitrothion was more
concentrated in fish than in the water. The concentration coefficients were highest
at low concentration. For example, in grass carp at application rates of 0.05 ppm,
they were 12, 39, and 10 from 2 to 24 h; whereas, at 1-2 ppm the concentration
coefficients ranged from 1 to 3. The concentrations were higher for common carp
and crucian carp (5.4-7.5).
The amount of fenitrothion (Table 6) in water decreased from 2 to 8 h then
increased by 24 h; whereas, in the fish, the amount increased from 2 to 8 h and
then decreased. The amount in water probably reflects two processes: the natural
breakdown of fenitrothion in water, and the accumulation (2-8 h) and elimination
of the pesticide by the fish (24 h).
Table 7 indicates the elimination dynamics of fenitrothion from fish when used at
1 125 g/ha (50% EC 800 dilution) and shows a similar pattern to Table 6. The
results show that some of the pesticide in the water is absorbed by the fish after
application. The fish absorb fenitrothion quickly during the earlier stages, and the
concentration of the pesticide decreased in the fish 24 h after application. Other
experiments showed no difference between fish raised in ricefields and fish raised
indoors (Table 7).
The half-life of fenitrothion was 2 days and the residue curve formula was:
y =1.6282e-° 3559x
(r=0.9648)
to
£»
K>
2
o
Table 6. Accumulation and elimination of fenitrothion by different species of fish.
m
i
31
Grass Carp
0.05 ppm
CO
0.1 ppm
1 ppm
I
O
2 ppm
c
I—
Hours after
Application
Water
Fish
CCa
Water
Fish
CC
Water
Fish
CC
Water
Fish
CC
2
0.0489
0.600
12.3
0.0781
1.348
17.3
0.915
1.581
1.7
1.812
2.851
1.6
8
0.0394
1.522
38.6
0.0652
4.000
61.4
0.82
2.014
2.5
1.539
3.234
2.1
24
0.0720
0.730
10.1
0.104
2.920
28.1
0.843
0.962
1.1
1.781
2.091
1.2
Common Carp
1 ppm
Crucian Carp
2 ppm
1 ppm
2 ppm
2
0.824
3.981
4.8
1.820
5.612
3.1
0.651
2.96
4.6
1.225
5.442
4.4
8
0.605
4.674
7.7
1.239
7.510
6.1
0.533
4.018
7.6
1.06
7.085
6.7
24
0.771
2.586
3.4
1.523
6.361
4.2
0.632
3.27
5.2
1.741
5.825
3.3
* CC concentration coefficient.
c
3D
m
z
o
I
z
>
INTERACTIONS
243
Table 7. Elimination of fenitrothion from fish in ricefields
when used at 1 125 g/ha (50 EC 800 dilution).
2h
Residue
8_h
W
F
W
0.39
1.25
0.35
-
-
-
Rate
24 h
F
W
F
2.53 0.06
-
72 h
W
120 h
F
1.75 0.03
W
148 h
F
0.33 0.02 0.09
W
F
0.01
0.05
81.18 30.74 92.20 95.38 95.38 96.48 97.46 98.22
* W water; F fish; R digestion rate.
Table 8. Residues of fenitrothion in fish that underwent purification.
Common Carp
b
24.815
IET
Fish
ER
Crucian Carp
25.827
Fish
1
14.915
39.9
16.018
3
4.510
81.9
5
0.713
7
0.031
ER
26.315
Fish
ER
Grass Carp
28.210
Fish
18.513
ER
Fish
20.007
ER
Fish
ER
38.0 18.210
35.8 16.515
37.2 12.001
35.2 13.015
35.0
4.785
81.5
5.860
79.2
5.003
81.0
3.212
82.7
3.810
80.9
97.1
0.815
96.8
0.880
96.9
0.850
96.8
0.071
99.6
0.075
99.7
98.8
0.041
98.4
0.048
99.8
0.043
98.4
0.011
99.9
0.014
99.9
* IBT interval between treatments (days); ER elimination rate (%).
b
Numbers in this row are the concentrations of fenitrothion at the beginning of the test.
Table 9. The distribution of fenitrothion in fish and viscera in 0.346 ppm water.
Distribution of Fenitrothion
Fish
Viscera
Residue
(ppm)
Concentration
Coefficient
Residue
(ppm)
Concentration
Coefficient
Common carp
18.21
52.95
65.11
188.18
Crucian carp
19.38
56.01
68.21
197.21
Grass carp
12.11
35.00
25.31
73.16
When fish are exposed to fenitrothion, they both absorb and accumulated and
degrade and eliminate the chemical. Accumulation and elimination of fenitrothion
are kept in a dynamic balance. In a polluted environment, toxic pollutants are
244
RICE-FISH CULTURE IN CHINA
concentrated and accumulated by fish. When the fish are in a nonpolluted
environment, the chemical is eliminated. Fish are an important part of the food
chain. Fenitrothion was accumulated in the polluted ricefield ecosystem. Different
fish concentrated the fenitrothion at different rates.
Experiments were also carried out to determine the rate of fish purification.
Table 8 shows the results of the purification experiments. Although the pesticide
broke down quickly in the fish and the ricefields, these purification measures could
speed up the elimination of pesticides from the fish.
Distribution of Fenitrothion
Residual fenitrothion was detected in fish in ricefields in 12 cities and counties in
Sichuan Province. Middle-season rice is normally treated with 560-750 g/ha (50%
EC 800 dilution) sprayed from one to three times through the season. Three
hundred samples of rice and fish were obtained through out Sichuan. The residue
level in rice grains was 0-0.027 ppm, the residue level was from trace to
0.077 ppm in rice bran, and the level was 0-0.037 ppm in fish. The concentration
of fenitrothion was higher in the viscera than in the meat of the fish (Table 9).
Summary
Fenitrothion is a pesticide with high efficacy, low residues, and low toxicity.
Contamination should not occur in the aquatic ecosystem of the ricefield when
fenitrothion is used. Fenitrothion could be promoted to increase outputs of rice and
fish.
The residual standard for fenitrothion in rice grains has been set at 0.2 ppm in
China. There is no standard for the maximum residue in fish, but in Japan it is
0.05 ppm. If the pesticide is applied as recommended and not close to the harvest
time for the rice and fish, the residues should be well below acceptable levels.
Fenitrothion should not produce lasting accumulations in rice and fish because its
degradation rate is fast (LH50 2 days). If the concentration of toxic pollutants is
controlled in the water, there should be no long-term contamination of fish.
Part IV:
Economic Effects
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Economic Analysis of Rice-Fish Culture
Lin Xuegui, Zhang Linxiu, and He Gutting68
Rice-fish culture has received much attention since the 1980s. Rice-fish farming
methods have increased both rice yields and economic benefits. The area devoted
to rice-fish culture has expanded rapidly from 345 000 ha in 1982 to 558000 ha
in 1984, an increased of 62%. The yield of fish products has also increased from
24000 tonnes 56300 tonnes, an increase of 135%. Fish culture in ricefields has
become an important component of freshwater fish production.
To evaluate rice-fish culture, its economic benefits must be compared with singlecrop rice production. Moreover, comparisons between rice yields in rice-fish
culture and in single-crop ricefields are needed to estimate the effects of rice-fish
coexistence on rice yields. Twelve farm households in Hong'an and Hanchuan
Counties, Hubei Province, were interviewed in June 1988. Among these
households, four planted only rice and were used as the control. The other
households adopted various types of rice-fish culture. The study used cost-benefit
analysis to assess the various economic criteria of rice-fish culture.
Comparison with Single-Crop Rice Production
Survey data were collected from four farm households in Hong'an County, Hubei
Province. The households practiced two farming types: rice-fish and single-crop
rice. Although the two groups of households had similar conditions (e.g., scale of
production, soil fertility, and production technologies) both the production value
and economic benefits of the rice-fish households were higher (Table 1).
Yield Increase
In addition to the 253.5 kg/ha of production of fresh fish, rice yields with rice-fish
culture were 7.8% higher. Rice and fish together produced a total product value
that was 41% higher than from rice alone. In terms of protein output, rice-fish
culture was 26.8% higher. Of the increase in protein, more than 70% was
accounted for by fish protein (Table 2).
Relative Economic Benefit
Whether rice-fish culture can substitute for single-crop rice production depends on
its relative economic benefit. Various resource productivity criteria (e.g., land pro-
68
Institute of Agricultural Economics, Chinese Academy of Agricultural
Sciences, Beijing.
248
RICE-FISH CULTURE IN CHINA
Table 1. Basic characteristics of sample households.
Rice-Fish Culture
Single-Crop Rice
2
2
Education level of householder
middle school
middle school
Average area of ricefield (ha)
0.2
0.2
middle
middle
Seeds (kg)
12.5
12.5
Fertilizer (CNY)
13.2
12.7
Animal labour (days)
3.5
3.5
manual
manual
Sample size (no.)
Soil fertility of ricefield (Grade)
Farm tools (type)
Table 2. Outputs of different farming types.
Farming Type
Yield (kg/ha)
Value Product (CNY/ha)
Rice
Fish
Rice
Fish
Total
Protein Yield
(kg/ha)
Rice-fish
8250.0
253.5
2970.0
912.0
3882.0
394.5
Single-crop rice
7650.0
-
2754.0
-
2754.0
310.5
Increase
600.0
253.5
216.0
912.0
1128.0
84.0
7.8
—
41.0
13.4
Percentage
increase
7.8
-
ductivity, labour productivity, and capital productivity) were used to measure the
relative economic benefit of rice-fish culture. The analysis showed that net income
per unit input, net return to labour, and benefit-cost ratio were significantly higher
for rice-fish culture (Table 3).
When extending new agricultural technologies, changes in socioeconomic factors
(e.g., market institutions and new farming practices) can affect efficiency. The risk
and uncertainty associated with of agricultural production mean that the economic
benefits of new technologies must reach a certain level. Many countries use two
indicators (the increment in economic benefit and marginal benefit-cost ratio of
new technology) and set their critical values at 30% and 2, respectively. In China,
these two values are 18-22% and 1.2-1.5, respectively. The results of our analysis
indicate that these two indicators for rice-fish culture are 45% and 2.5,
respectively.
ECONOMIC EFFECTS
249
Table 3. Economic benefits of different farming types.
Rice-Fish
Culture
Single-Crop
Rice
2185.50
1506.90
+45.0
10.06
8.93
+12.6
Net return to material inputs
(CNY)
3.15
3.28
-4.0
Benefit-cost ratio
2.29
2.20
—
Farming Type
Net benefit (CNY/ha)
Net return to labour
(CNY/person-day)
Percentage
Difference
The economic benefits of rice-fish culture were related to:
•
•
The increase in rice yields and the saving in labour and material
inputs. Compared with single-crop rice production, rice yields in
rice-fish culture were 7.8% higher, labour input were 19.4%
lower, and material costs were 7% lower because of savings in the
control of plant diseases and pests.
The increase in net benefits because of fish production
(CNY286.5/ha).
Different Patterns of Rice-Fish Culture
After the system of rice-fish culture is adopted, further increases in economic
benefit can be realized by improving the combinations of rice and fish and by
designing and choosing different kinds of component technologies.
In Hanchuan County, Hubei Province, three different patterns of fish culture are
used: breeding fingerling in ricefields, breeding adult fish in ricefields, and
breeding both fingerling and adult fish in ricefields.
To determine the best pattern of rice-fish culture, the economic benefits of the
different patterns of rice-fish culture were compared using relative indicators of
economic benefit (Table 4). The values of both indicators (increment in net benefit
and marginal benefit-cost ratio) exceed the lowest limit (critical value) for
spreading new technology. It is difficult to determine which method is the best just
by studying these two indicators. There are trade-offs between them. Based on the
net benefit, mixed culture was the best pattern. Based on marginal benefit-cost
ratio, breeding fingerlings is the best pattern. Therefore, it is necessary to consider
some other indicators. It is generally agreed that the criterion of economic
assessment for new technologies should be the maximum value of economic
results. To modify the criteria, three indicators (net profit/area, output value/input
costs, and net profit/input costs) were used. These three indicators valued mixed
culture the highest (CNY259.43, CNY3.76, and CNY2.76, respectively). The net
250
RICE-FISH CULTURE IN CHINA
Table 4. Economic benefits of different rice-fish combinations.
Fingerling
Breeding
Adult Fish
Breeding
Mixed
Breeding
Single-Crop
Rice
Increment in net benefit
CNY/ha
%
Marginal benefit-cost ratio
1180.65
2051.70
2217.75
-
70.5
123
132
-
5.26
4.93
5.11
2854.20
3725.40
3891.45
—
Net benefit per unit
CNY/ha
%
171
223
233
1673.70
100
Value product per unit of cost
CNY/CNY
%
3.48
3.68
119
126
3.76
129
2.90
100
Net benefit per unit of cost
CNY/CNY
%
2.49
2.68
130
146
2.76
144
1.92
100
Cost per unit of value product
CNY/CNY
0.27
0.27
80
%
80
0.27
78
0.34
100
Table 5. Component technologies of different rice-fish combinations.
Double
Rice-Fish Culture
(Group A)
Double
Rice-Fish Culture
(Group B)
2
2
Average farm size (ha)
0.21
0.15
Area of rice (ha)
0.19
0.13
Area of fish (ha)
0.02
0.02
Fertilizer
223.4
116.6
Seeds
35.2
24.2
Pesticides
32.0
22.0
Fingerling
65.6
41.4
Feed
144.0
48.4
Others
25.6
17j5
Sample size
Inputs (CNY)
ECONOMIC EFFECTS
251
Table 6. Economic analysis of component technologies.
Double
Rice-Fish
(Group A)
Double
Rice-Fish
(Group B)
Group A/
Group B
Difference
Rice
1272.0
1020.0
252.0
Fish
1192.5
822.0
370.5
Rice
720.0
780.0
-60.0
Fish
810.0
690.0
120.0
3994.5
3312.0
682.5
16620.0
15150.0
1470.0
Value of product (CNY)
5983.5
5454.0
529.5
Fish
Value of product (CNY)
1710.0
732.0
979.5
Total
Value of product (CNY)
7693.5
6186.0
1507.5
3699.0
2874.0
825.0
Inputs (CNY/ha)
Materials
Labour
Total
Outputs
Rice
Yield (kg)
Net benefit (CNY/ha)
profit was 1.3 times that of single-crop rice production, 4.5% higher than adult
fish culture, and 36.3% higher than fmgerling culture.
Factors Affecting Economic Benefits
In rice-fish culture, there are differences in methods of using the ricefield, patterns
of rice-fish culture, combinations of inputs, combinations of fish, and ways of
breeding. All these differences can affect the economic benefits of rice-fish
culture.
Tables 5 and 6 present data from Hanchuan County, Hubei Province. The inputs
and outputs of two types of rice-fish culture were studied. The net benefit of group
A was CNY825/ha higher than group B. The net benefits of rice increased by 41 %
and the net benefit from fish increased by 59%.
The benefit-cost ratio of group A was 3.9% higher than group B. The higher
economic benefits of group A were mainly due to the effects of higher inputs and
the combination of different kinds of fish species.
252
RICE-FISH CULTURE IN CHINA
Conclusion
Rice-fish culture is one way to increase the economic benefits from ricefields and
develop freshwater fisheries. Rice-fish culture increases rice output. The average
value of products can be increased by 41 %, the rice yield by 7.8%, and the protein
output by 26.8%. The increase in protein output is mainly animal (fish) protein.
When deciding whether to extend new agriculture technology, the economic
evaluation usually requires that the increment in economic benefits and the
marginal benefit-cost ratio must be more than 18-22% and 1.2-1.5, respectively.
These two indicators in rice-fish culture were over the critical value. Compared
with single-crop rice production, net profits from rice-fish culture were 45%
higher, the rate of return to labour was 12.6% higher, and the benefit-cost ratio
was 4% higher. The main reasons for higher economic benefits from rice-fish
culture were:
•
•
Increase in rice yields and saving on labour and material inputs.
Increases in net profits from fish production.
Once rice-fish culture has been adapted, further increases in economic benefits can
be realized. The net benefits from rice production combined with adult fish and
fingerling production was 4.5% higher than from the combination of rice and adult
fish, and 36.3% higher than from the rice-fingerling combination. Research to
improve the component technologies may further increase economic benefits.
The ecological benefits of rice-fish culture were related to weeding, elimination
of insect pests and diseases, preserving and increasing the fertility of the soil,
environmental stability, and improving environmental conditions.
These results indicate that rice-fish culture provides technical, economic, social,
and ecological benefits. In addition to technical knowledge, several conditions must
be met to implement rice-fish culture:
•
•
•
•
The field must have a good irrigation and drainage system to ensure
that there is no water logging during the rainy season and that the
field does not dry out during droughts.
Field ridges and fish ditches must be created to meet the different
water requirements of rice and fish.
High efficiency, low toxicity pesticides must be selected to avoid
toxic effects on fish.
A resource plan must be implemented to use resources rationally,
increase rice yields, and optimize economic benefits.
Economic Research on Rice-Fish Farming
Jiang Ci Mao and Dai Ge69
Since 1978, rice-fish culture has developed very rapidly in China. The area under
production has continued to expand, and aquatic production has increased each
year. In some provinces, rice-fish production accounts for the largest percentage
of freshwater fisheries production (Table 1).
The development of rice-fish farming differs from place to place. In China,
rice-fish culture accounted for 2% of freshwater aquatic production in 1982. In
1983 and 1984, the proportion was 2.5% and 3.1% respectively. In Sichuan,
rice-fish culture now accounts for 7.6% of freshwater aquatic production.
Rice-fish culture is important part of fisheries production in Sichuan, Guizhou,
Hunan, and Jiangxi. In 1949, production from rice-fish culture accounted for
15.5% of the aquatic production of these four provinces. By 1984, this figure was
21.6%. In Guizhou, rice-fish culture represents 75% of total aquatic production.
In these provinces, rice-fish farming is common in the hilly and mountainous
areas. For example, in Sichuan and Guizhou, about 75% of the production comes
from these areas; whereas, in Quin Dong Nan, Guizhou, 85% of aquatic
production is supplied by rice-fish farming.
Ricefields are a suitable place for the culture of fry and fingerlings. In Hunan
Province, 0.44 billion fish were breed in 38 430 ha of ricefields and ponds. These
fry and fingerlings can be used to promote fish production in ponds, reservoirs,
and lakes.
Economics of Rice-Fish Fanning
A survey of 23.8 ha of rice-fish fields was conducted in Jiangxi Province in 1984.
The average input cost was CNY660/ha and the average net profit from breeding
and selling fish was CNY4590/ha. The cost-return ratio was 7.9. Similar surveys
were undertaken in Hunan and Guizhou. In Hunan, a survey of 7.3 ha of ricefields
in 1984 showed that the cost-return ratio was 16.0; whereas, in Guizhou, 222.4 ha
were surveyed and the ratio was 7.8. For China as a whole, the maximum cost of
the rice-fish farming is about 20% of the value of production (input: output ratio
1:5). From these calculations, it can be seen that rice-fish farming provides a good
return on investment.
69
Aquatic Bureau of Sichuan Province, Chengdu, Sichuan Province.
254
RICE-FISH CULTURE IN CHINA
Table 1. Fish production from ricefields (as percentage of total fish production) in China
and several provinces (1983 and 1984).
1983
1984
China
2.54
3.11
Jiangsu
—
0.18
Zhejiang
0.77
1.28
Anhui
0.55
1.12
Fujian
3.90
5.39
Jiangxi
1.90
3.40
Hunan
4.31
5.76
Guangdong
0.21
0.45
Guangxi
3.82
4.59
Sichuan
22.29
25.16
Guizhou
79.25
71.08
4.93
7.53
Yunan
Table 2. Production value of rice-fish culture in Chengdu, Sichuan Province (1984).
Rice
Fish
Ratio TV
Type of Area TV* to Rice
Ricefield (ha)
kg/ha CNY/ha kg/ha CNY/ha (CNY/ha) Only (%)
Plains
2-season
field
206
7895
2053
373
1119
3172
54.5
Hills
Winter
ricefield
80
7670
1994
688
3945
5534
177.5
' TV total value.
Techniques and Management
Common carp, crucian carp, grass carp, and nile tilapia are raised in ricefields.
The integration of fish and rice provides several benefits (e.g., pest control,
fertilizer, and reduced need for pesticide). In general, rice-fish culture is a simple
technique that is easy to popularize because there is little risk.
Farmers in economically developed areas are not as interested in rice-fish culture
because they have relatively high incomes from other means. But for farmers in
remote areas, the situation is quite different. In these areas, farmers have few
income sources other than crop production. Therefore, rice-fish culture is
ECONOMIC EFFECTS
255
attractive because of its low cost and good return. It is one of the best ways for
remote areas to improve their economic development.
Rice-fish culture can also be easily popularized in the areas adjacent to cities and
towns. Areas adjacent to cities and towns have the advantages of access to
information and speed of market feedback. The site of production and the market
are close together and the selling price of the fish is relatively high. Therefore, the
return on investment is higher than in remote areas.
Rice-Fish Farming and Agriculture
Rice and fish are mutually beneficial. Fish can accelerate the growth and increase
the production of rice. A large-scale survey of rice-fish culture indicated that rice
production was increased by 5-15%. Rice-fish culture, beyond doubt, can promote
agricultural production and development.
Economics
Before rice-fish culture was introduced in Sichuan, the average rice yield was
about 6000 kg/ha and the income was CNY1755/ha. However, when fish were
raised in ricefields, the increase in income was CNY150/ha from rice and
CNY750/ha from fish. In some areas, the income from selling fish was even higher
(Table 2). The production value of rice-fish farming is much higher than rice
production alone. Especially in hilly areas, there are many winter ricefields that
have deep water storage and hold water for a relatively long time. Under these
conditions, the value of rice-fish culture is about three times rice production alone.
Compared with the cost of rice production, which is about 30-50% or even 60%
of the value of rice production, the cost offish grown in ricefields is relatively low
(about 20% of the value of production). The economic benefit of rice growing is
not as high as fish culture. At present, the unit yield of rice is stable. It is difficult
to raise the economic benefit of the ricefield by increasing rice yield. However,
improved benefits and production values can be achieved by raising fish in
ricefields. Generally, from rice-fish culture the net income will be about
CNY600/ha. A maximum net income of about CNY1 500/ha is possible and is the
goal of many farmers (Table 3).
Fish bring changes to rice cultivation and help achieve remarkable economic
benefit. These changes mainly decrease inputs into rice cultivation. The fish eat
weeds that compete with rice for fertilizer. The fish also help control plant diseases
and insect pests and, therefore, reduce the need for pesticides and the amount of
labour needed for weeding. Studies in Sichuan, Hunan, Guizhou, and Jiangxi
showed that raising fish in ricefields saved about 8-12 days of labour.
Rice-fish culture improves labour productivity. Labour productivity is a measure
of the total products produced in a certain period. Labour productivity reflects the
Table 3. Economic benefits from different forms of fish culture in Sichuan in 1984.
to
Cft
ON
Average Inputs
per ha
Area
(x 1 OOP ha)
Raising
Days
Rice only
46.7
-
Rice-fish
4.8
65
Avg. Fish
Harvest
(kg/ha)
Avg. Rice
Harvest
(kg/ha)
Total Income
(fish +rice)
Labour
(1 day)
Net
Invest.
(CNY)
Avg.
Income
(CNY/ha)
-
4883
1689
240
450
639
113
5250
1913
285
480
720
Income
Ratio
(%)a
Hunan
3J
O
m
i
•^
u>
I
O
113
c
f—
c
33
m
Rotation fish 0.5 200 600 6750 3534 311 750 2001 313 Z
O
and rice
I
Intercrop, rice 0.7 35 Raising fry 5250 2484 285 858 998 156
and fish
Sichuan
Rice only
8.2
Rice-fish
0.3
-
-
5273
2109
240
675
1434
-
70-90
83
5438
2472
300
837
1635
114
Rotation fish 0.2 200-240 128 5513 2588 315 930 1658 116
and rice
Fish culture in
half-dry fields
0.08
90-100
879
8513
6026
375
1320
4706
328
Fish culture
(ponds+canals)
0.08
90-100
885
7575
6216
27
1335
4881
340
* Net income from fish culture in ricefields as a percentage of income from planting only rice. Labour in Hunan is CNY2.5/day. Net income of
Qingcheng in Sichuan includes labour price.
Z
>
Table 4. Labour productivity of rice-fish culture in Hunan and Sichuan (1984).
Labour
(days/ha)
Labour Productivity
(Production
Value/Labour Day)
(CNY)
Labour Productivity
of Ricefish Culture
per Pure Rice
Planting (%)
1689
240
7.04
—
4.8
1913
285
6.71
95.3
0.5
3534
311
11.38
161.7
Area
(x 1 OOP ha)
Average Output
(Fish + Rice)
(CNY/ha)
Rice only
46.7
Fish in ricefields
Rotation of fish and rice
Form of
culture
Hunan
Intercropping of rice and fish 0.7 2484 285 8.71 123.6
Sichuan
Rice only
8.2
2109
240
8.78
-
Fish in ricefields
0.3
2472
300
8.24
94.7
Fish culture in half-dry ricefields
0.08
6026
375
16.07
184.7
m
O
O
Z
O
Z
O
m
-n
-n
m
O
H
C/)
N>
<J\
-J
258
RICE-FISH CULTURE IN CHINA
Table 5. Survey of rice-fish culture in Sichuan and Jiangxi in 1984.
Total Production
of Fish + Rice
(CNY/ha)
Fish Production
Value
(CNY/ha)
Increase Because
of Fish Culture
(%)
Chengdu Plains
3172
1119
35.3
Hills
5534
3945
71.3
7779
5253
67.5
Sichuan
Jiangxi
level of fish-raising in ricefields. Low-level rice-fish farming has lower labour
productivity than rice farming. When the ricefield is used to cultivate fry and
fingerling the labour input is increased a little. Much higher labour productivity
can be achieved by adopting new technical improvements (Table 4).
Land and Water Resources
China is a large country with a large population and a scarcity of agriculture land.
Agricultural production occupies an important place in the national economy;
therefore, comprehensive use of land and improvements in grain production are
important. Rice-fish culture has many advantages: increases in grain yield,
production of freshwater fish, an increase in the production capacity of arable land,
increased economic returns, and a higher land-utilization ratio (Table 5).
Rice alone cannot make full use of the materials and energy in the ricefield.
Rice-fish culture can greatly increase the use of fertilizer and energy, and
transform these materials into human food. Water is a precious natural resource.
Rice-fish culture makes more comprehensive use of available aquatic resources.
The efficiency of water use is increased because more than one use is made of the
water.
Ecology and Economics of Rice-Fish Culture
Quing Daozhu and Gao Jusheng70
The hilly district in the south of Hunan Province is one of the birthplaces of fishrearing in mountain ponds and in ricefields. The area devoted to rice-fish culture
was 30000 ha in 1987. In Qiyan County alone there were 10000 ha. Rice yields
range from 7500 to 13500 kg/ha, yields of fresh fish from 450 to 750 kg/ha, and
output values from CNY6000 to CNY10500/ha. The economic and ecological
effects of rice-fish culture are remarkable. Research on high-yield technology
systems and the ecological and economic effects of rice-fish culture has been
conducted since 1985.
Materials and Methods
Grass carp, silver carp, common carp, variegated carp, and crucian carp were
tested. Summer fingerlings (3-5 cm long) were reared in the rice nursery of late
rice for 20-30 days. They were stocked in the ricefields at the end of May or the
beginning of June. Different rice varieties were grown each year: early rice
(Zhuxi 26) and late rice (V64) in 1985, early rice (Zhuxi 26) and late rice (79-16,
a strain with disease resistance) in 1986, and early rice (V49) and late rice (V64)
in 1987. The size of the transplanted rice varied according to rice cultivars. The
other planting conditions were: hill spacing 13 cm x 20 cm, 7-8 seedlings per hill,
and 375000 hills/ha for common rice, and hill spacing 17 cm x 20 cm,
2-4 seedlings per hill (including tiller), and 300000 hills/ha for hybrid rice.
The experiments were conducted in a gleyed ricefield in Guangshanping Village
in Quiyang County and in a ricefield with a green manure crop on the farm of the
Hangyan Red Loam Experimental Station. The experiment included four treatments
(no reph'cations): ridge culture with tillage (RCT) in the gleyed ricefield (control,
0.03 ha), ridge culture with no tillage (RCNT) in the gleyed ricefield (0.03 ha),
fish-rearing and ridge culture with no tillage (FRCNT) in the gleyed ricefield
(0.12 ha), winter crop or green manure crop plus fish and early rice with ridge
culture and tillage plus fish and late rice with no tillage (W-FRT-FRNT) (0.11 ha).
About 7-10 days before the rice seedlings were transplanted, 1.2-m wide ridges
were made. The furrows were 30 cm wide and 20 cm deep (the main ridge furrow
was 40 cm wide and 30 cm deep). The fish pit was 3 m x 3 m. Decomposed pig
and cow manure (1500 kg) was applied to the surface of soil before ridging. Urea
70
Hengyan Red Loam Experimental Station, Chinese Academy of
Agricultural Sciences, Hengyan, Hunan Province.
260
RICE-FISH CULTURE IN CHINA
Table 1. The number of weeds per square metre with two rice-fish culture methods
using early rice cultivar Weiyou 49 (1987).
Species of Weed"
RCNT*
1
2
3
4
5
6
7
22.0
3.5
0.3
-
few
few
many
FRCNT 5.0 - - - 00
"Weeds: 1 Monochoria vaginalis, 2Echinochloa crusgalli, 3 Scripus maritimus, 4 Ammannia
baccifera, 5 Eleocharis acicularis, 6 Potamogetonfranchetii, and 7 Azolla pinnata.
k
RCNT ridge culture with no tillage, FRCNT fish-rearing and ridge culture with no tillage.
(150 kg/ha), calcium superphosphate (450 kg/ha), and potassium chloride
(150 kg/ha) were applied on the surface of the ridge before the rice seedlings were
transplanted. In addition, 112.5 kg/ha of urea were broadcast.
Analysis of Experimental Results
Effect on Rice Growth
Rice-fish culture is a high-yield technology that makes good use of available
resources and provides ecological benefits. To compare the effects on rice growth
of different methods of planting and rearing, observations were made on the
dynamics of rice tillering. There were no great difference in the number of rice
stems (including tillers) in the early stage among RCT, RCNT, and FRCNT. The
differences increased in the middle-late stage. The numbers of rice stems
(including tillers) in the peak tillering stage were: 8 million/ha in the field with
RCT, 6 million/ha with RCNT, and 5 million/ha with FRCNT. However, the
difference in effective panicles became smaller at maturity. In the ACT field, the
rice grew quickly and there were more tillers, but there were also more ineffective
tillers and the percentage of ear-bearing tillers was low. In this field, there were
5.5 million ear-bearing tillers per hectare and the rate of ear bearing was 69.2%,
with RCNT there were 4.7 million ear-bearing tillers per hectare and the rate of
ear bearing was 78.1 %, and with FRCNT there were 4.1 million ear-bearing tillers
per hectare and the rate of ear bearing was 81.2%. The number of ineffective
tillers was lower but the rate of ear bearing was higher in the rice-fish fields
because the small tillers at the base of the rice plant were eaten by the fish.
Weeds, Diseases, and Pests
During the vegetative cycle of the rice, there were almost no weeds with rice-fish
culture because the weeds became the natural food of the fish. There were
15 species of weeds in ricefields with RCT and RCNT. Monochoria vaginalis (21.8
and 22.0 plants/m2) and barnyard grass (Echinochlea crugalli) (4.0 and 3.5
plants/m2) were the most common weeds (Table 1).
ECONOMIC EFFECTS
261
Table 2. Relationship between the incidence of rice diseases and insect pests and rice-fish
culture in fields of the early rice cultivar Weiyou 49 (1987).*
Rice Sheath
Blight Disease
(%)
Rice Leafroller
(No./lOO hills)
RCT
2.1
5.71
RCNT
3.9
4.25
FRCNT
6.3
4.08
" Data were obtained during the rice booting stage (21 June). RCT ridge culture with tillage,
RCNT ridge culture with no tillage, FRCNT fish-rearing and ridge culture with no tillage.
Table 3. The influence of different forms of rice-fish culture on the economic properties
and yield of the early rice cultivar Weiyou 46 (1987).
RCT
RCNT
FRCNT
Effective panicles (1000/ha)
372
322
292
Grains (no./panicle)
103.5
106.4
137.2
Setting percentage
71.6
72.4
64
Weight of 1000 grains (g)
26.8
26.5
27
Yield (kg/ha)
8194
8058
7454
' RCTridgeculture withtillage,RCNTridgeculture with notillage,FRCNTfish-rearingand
ridge culture with no tillage.
Table 4. Economic benefits offish-culture and rice ridge culture.
Year
Annual
Rice
Yield
(kg/ha)
Field with winter crop 1985 9774
or green manure
Annual Percentage
Rice
Fish
Total
Total
Value"
Income
Income
Income
(CNY/ha) (CNY/ha) (CNY/ha) from Fish
3909
813
4723
17.2
1987
11282
4513
2650
7159
37.0
Gleyed ricefield
1985
12869
5147
2258
7405
30.5
Field (winter)
1986
11162
4465
1664
6129
27.2
1987
13124
5249
3611
8860
40.8
Winter-water
field
* Price of rice CNY40/100 kg; fish at market price each year.
262
RICE-FISH CULTURE IN CHINA
The results were different for insect pests and rice diseases. The incidence of
sheath blight disease was 6.3% in the rice-fish fields compared with 3.9%
2.1% in the field with RCNT and RCT, respectively. The number of
leafrollers in the rice-fish fields was 4.1 heads per 100 hills compared with 5.7
4.3, respectively, in the fields with RCT and RCNT (Table 2).
rice
and
rice
and
Fish rearing reduced the amount of pesticides and the frequency of spraying. As
a result, beneficial organisms were increased. For example, there were 380 000 red
mites per hectare in the rice-fish fields compared with 65 500-86 000 in ricefields
without fish. There were also nearly twice as many frogs.
Soil Fertility
Ridges help raise the soil temperature of the cultivated layer, which promotes the
conversion of potential nutrients. Fish in the ricefields fertilize the soil with their
excrement. Analysis of soil samples taken from the cultivated layer after rice and
fish were harvested indicated that organic matter content was 4.11%, total nitrogen
0.21%, total phosphorous 0.09%, alkali-hydrolyzable nitrogen 152.72 ppm, and
content of available phosphorus 9.85 ppm. The same measures of soil samples
from fields without fish were slightly less: 4.0%, 0.2%. 0.08%, 127 ppm, and
4.5 ppm, respectively. Soil nutrients were higher in rice-fish fields than in riceonly fields.
Rice Yield
Fish culture lowered rice yields. The number of effective panicles was highest in
the field with RCT and lowest with FRCNT. Rice yields were 8 195 kg/ha with
RCT, 8058 kg/ha with RCNT, and 7454 kg/ha with FRCNT (Table 3).
An analysis of 13 samples taken between 1984 and 1986 showed that the difference
in rice yield between RCT and RCNT was not significant. The rice yield from
ridge culture was not significantly different between RCT and RCNT, but both
were higher than the yield from the rice-fish field. However, in the gleyed field,
zero tillage not only saved labour, but shifted the time of transplanting to earlier
in the season. The adoption of no tillage also greatly reduces mechanical damage
to fish and enhance their survival. This promotes higher yields of both rice and fish
and increases the total value of the output.
Economic Benefits
When developing a plan for field engineering and cultivation technologies, the
basic principle is that rice is the main crop and fish is the secondary one. The
establishment of a good ecosystem makes full use of space, land, and water in the
ricefield and to greatly raises the biomass and total value of the output of the
ricefield with little extra more input or cost.
From 1985 to 1987, the experiment on fish-farming and ridge culture of rice with
no tillage produced 9774-13 124 kg/ha of rice (both early and late rice). The value
263
ECONOMIC EFFECTS
Table 5. Cost and survival rates of fish reared in 0.6 ha of ricefields (1985-1987).
No. of
Fish
Stocked
No. of
Fish
Harvested
Survival
Rate
(%)
Cost of
Fish
(CNY)
Income
from
Net
Percentage
Fish
Income of Each
(CNY) (CNY)
Species
Grass carp
16000
4928
30.8
49.0
854.2
805.2
65.5
Silver carp
2460
522
21.2
10.7
157.6
146.9
12.0
Common
carp
2650
1025
38.7
24.6
150.4
125.8
10.2
300
160
53.3
3.5
31.6
28.1
2.3
42500
6920
16.3
26.9
149.5
122.6
10.0
114120
24210
21.2
204.9
2398.5
2193.8
-
Crucian
carp
Other
Average/ha
Table 6. Economic effects of rice-fish culture.
Cultivating Method"
Rice
Value of
Fish
Increased
Early Late
Yield
Rice
Income
Income
Rice Rice Winter (kg/ha) (CNY/ha) (CNY/ha)
(%)
Gleyed field 1985
(control)
T
T
12192
4877
-
-
ZT
ZT WWF
11637
4655
-
-4.8
Green manure 1985
or winter crop
T
ZT
GM
9774
3909
813
-3.3
1987
ZT
ZT
Barley
11282
4513
2647
31.9
1985
T
ZT
WWF
12519
5008
2258
32.9
1986
ZT
ZT
Fish
11162
4465
1664
20.4
1987
ZT
ZT
Fish
13124
5249
3769
45.9
1987
Gleyed
field
WWF
" T tillage, ZT zero tillage, WWF winter-water fields, GM green manure.
of the rice was CNY3 909-5 349/ha and the value of the fish was
CNY813-3610/ha. Total income increased by 17-41%, a significant economic
benefit. Among different types of ricefields, rice yields and fish income differed
greatly. In the fields of winter rice or winter green manure, water deficits during
growth of late rice affected both rice and fish. As a result, rice yields were only
9774-11282 kg/ha, which was 12-14% lower than from the winter-water fields.
264
RICE-FISH CULTURE IN CHINA
The income derived from fish in the winter-rice or green-manure field was
CNY813-2650/ha and the fish income in the gleyed ricefield was CNY2258/ha
(Table 4).
The best choices for rice-fish fields are winter-water gleyed fields that have plenty
of water, but are easy to drain. Under these conditions, good growth of both fish
and rice are ensured.
Polyculture
There are many types of rice-fish farming. Most farmers still use the traditional
method of a level field to rear small-size common carp fry in natural water. As a
result, fish output is low, commonly 150-300 kg/ha from one-season ricefields.
Because the price of common carp is only CNY2-3/kg, fish income is also low.
Some farmers also maintain 3-4 cm of water in the field for a long time for the
sake of fish. This affects the growth and development of the rice and leads to a
reduction of rice yields and only slightly higher income from the fish.
A complete set of technological measures were applied in these experiments: the
rice was planted on ridges, early rice (middle-late maturing variety) was selected,
plant spacing was reduced, and tillage was increased in late ricefields. Problems
of long-term submergence of the ricefield after the fish were reared were avoided.
Moreover, polyculture of 3-5 varieties of fish raised the survival rate and increased
the income generated from the fish (Table 5).
With polyculture, the value of grass carp contributed 65.5% of total fish income.
The survival rates for the different species were: variegated carp 53.3%, common
carp 38.7%, silver carp 21.2%, and other fish (e.g., crucian carp) 16.3%. From
1985 to 1987, the experimental area for fish farming in ricefields was 0.56 ha and
the average income from fish was CNY2 194/ha.
The main ecological models for rice-fish culture in ricefields are
rice-fish-duckweed and rice-fish. Rice-fish with ridge culture and no tillage was
compared with RCT and RCNT. For the rice-fish system, two types of fields
(winter ricefields and winter-water gleyed ricefields) were used (Table 6). The field
with RCT had an output value of CNY4 876/ha, which was 4.8% higher than with
no tillage. In the green-manure crop or winter-crop field with rice-fish, the output
value was 31.9% higher than with RCT. In the gleyed field with FRCNT, there
was an increase of 20-46% compared with RCT. There are clear the economic
benefits to fish-rearing and ridge culture of rice with no tillage.
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