Rice-fish systems in China

by Yixian Guo

Rice-fish farming, an age-old practice in China, can be traced back more than 1 700 years, although recently it has been largely ignored. Integrated rice-fish farming in China is generally characterized by four basic components: (1) extensive use of land; (2) low input; (3) low yield; and (4) household consumption of rice-fish farming.

After the founding of the People's Republic of China, the government organized farmers and encouraged them to develop integrated rice-fish farming systems. As a result, hectarage under rice-fish farming reached 700 000 ha in 1959, but sharply declined in the 1960s and 1970s due to wide use of pesticides, reformation of cropping systems and unfavourable national economic policy during the «cultural revolution» period (1966-1976). During this period, acreage of rice-fish farming dropped from 40 000 ha to 320 ha in Guangdong province and a similar drop from 230 000 ha to 5 300 ha was documented in Hunan province. However, during the recent «reformation» and «opening» period, the government is again encouraging the adoption of rice-fish farmers.

With farmer initiative and assistance from the government, the adoption of rice-fish farming is rapidly expanding. It has traveled from Guangdong province in the south to Hei-Long-Jiang province in the north and has reached historical proportions with more than 1 million ha in 1986. Sichuan, Hunan, Guizihou and Fujian are the top four provinces in China.

Rice-fish systems are principally found in the areas of the Yangtze River basin and other parts of southern China, although some rice-fish can be seen in northern provinces. The traditional rice-fish systems presented here are found in both irrigated and rainfed areas. The improved designs are principally found in irrigated conditions. Most rice-fish farmers in China are «cooperative farmers» with small landholdings of 1 500 m² or less. Normal fishpond size is usually 1 000 m².

Ridged-field rice-azolla-fish model

Major component technologies of rice-fish systems in China are presented here.

1. Appropriate construction of paddy field

• The traditional paddy field layout has no trench or pond in the field and the water storage capacity is limited. Fish growth is more directly affected by rice crop management, and the result is a low and unstable yield.
• Here are some trench-pond integrated rice-fish designs.

Design A: trench-pit design
This is an improved design with a small, shallow pit (1-2 m²) in the center of the field. Crossing trenches are dug to connect the pit to all side trenches. Increased water storage capacity offers a better refuge for the fish. This design raises rice yield by 10 percent and 1-2 times as many fish can be raised as compared with the traditional design.

Design B: trench-pond design
This design is a further improvement with a larger, deeper pond at one end of the field. Crossing trenches are also dug to connect the pond to all sides. This design significantly increases the water storage capacity and provides a better environment for the fish. It raises and stabilizes the yield of both rice and fish.

Ridged-field rice-azolla-fish model

This design was originally developed for swampy areas with the objectives of improving soil properties and increasing rice yield. Later it was, stepwise, integrated with azolla and fish. Rice is planted on the ridge, azolla as a feed for fish as well as a biofertilizer, and green manure and fish are stocked in the trenches.

Production data of rice-fish-azolla system
(irrigated lowland)

1 Chinese mu = 0.67 ha

Azolla is a small aquatic fern (usually 1-5 cm large) which can grow on saturated or moist soils. It is capable of doubling its weight in 3-5 days. Azolla has symbiontic bacteria which fix atmospheric nitrogen and can fix 3-7 kg N/ha daily. It contains 4 percent nitrogen on a dry-weight basis and is an excellent source of nitrogen fertilizer.

2. Basal fertilizer application

Physical injury to fish caused by inorganic fertilizers used in rice production can be a constraint to rice-fish systems. Necessary measures should be taken to minimize fish injuries. One such measure is to increase the amount of basal fertilizer application during the land preparation stage to approximately 80 percent of the total nitrogen and 100 percent of the total phosphorous requirement.

3. Transplanting

Reduced rice plant population within the ridged-field paddy design caused by the construction of trenches and refuge ponds is one farmer constraint to the practice of rice-fish systems. Farmers can lose as much as 10 percent of their paddy when constructing trenches and refuge ponds for rice-fish systems. To minimize reduced plant population (and potentially decreasing crop yield), plant spacing can be intensified by lessening the recommended distances between hills while maintaining the row spacing (20-25 cm). Normal hill spacing of 15-20 cm between plants can be cut in half, thus doubling the plant population in the side-rows of the trench.

4. Fish stocking considerations in rice-fish systems

• Grass carp, common carp, Nile tilapia and crucian carp are four predominant species for polyculture rice-fish farming in China. One such system involves four species: grass carp (Ctenopharyngodon idellus), Tilapia sp., common carp (Cyprinus carpio) and crucian carp (Carassius auratus), with the first two species making up the majority. The recommended mix is a 25-45 percent composition of both grass carp and tilapia (a total combined composition of 70 percent) with a 15 percent mix of both common and crucian carp (remaining 30 per- cent) at stocking rate of 2-3 m². This mix of species can give an optimal yield of both rice and fish.
• When stocking fingerlings in the pond or paddy, a large difference in water temperature between the container used to transport the fish and the paddy can lead to fish loss and a poor survival rate. Therefore, it is recommended to mix water from the paddy with water in the container to slowly regulate the temperature differences and allow the fish to adjust to the water temperature field.

5. Top-dressing fertilizer application

Top-dressing fertilizer is applied at the panicle differentiation stage (about 28-30 days to heading). A shallow layer of standing water in paddy is necessary for fertilizer application, but can increase the possibilities of injuring the fish. However, two alternatives exist which can help minimize these limitations.

• Slowly drain the water from the paddy allowing the fingerlings to return to the refuge trench/pond. As the water in the ridges almost dried up, the top-dressing fertilization (broadcast) can be applied, thus avoiding injury to the fish as well as achieving fertilizer efficiency. Two to four days after the fertilizer is applied, the field is again flooded.
• Fertilizer application can be done by deep placement by hand or by using machinery. The fertilizer should be applied at a depth of 8-10 cm. Fertilizer efficiency and reduced risk to fish health are also attained. (Note: The paddy should also be drained for application of the deep-placement method).

6. Pest management

• Many weed varieties found in the rice paddy are good feeds for grass carp. Stocking fry at 2-3 pieces/m² (2-3 cm long) and fingerlings at 2-3 pieces/10 m² or (8-10 cm long) one month after transplanting can help control weeds, thus, reducing the need for other weed-control techniques. As the fingerlings grow, daily supplemental feeding with green grasses is necessary to avoid damage to the young rice plants by the fish. Grass is usually fed to the fish in the pond to avoid damage to the rice plants; while rice bran and other supplemental feeds can be directly fed to the fish in the paddy area.
• Fish eat insects, such as stemborer and leaffolder which move through the water among the rice plants and hoppers which catch them as they float on the water from the rice plant. Fish reduce need for pesticide. They also eat the pathogens (such as sheath blight disease) floating in water and on the bottom as well as disease-infected leaves. This not only reduces the pathogens but also improves plant's health. The use of fungicides can also be reduced. If pesticides must be applied, certain precautions should be taken. Traditional fields should be flooded with more water.
• Pesticide application

Similar to fertilizer application, damage to fish health can be incurred with the application of pesticides to the rice crop. However, using simple techniques such as slow field drainage, allowing the fish to return to the trench/pond, cautious application of the pesticide, an allowance for a brief waiting period and re-irrigation of the field after application can help ensure minimal losses due to pesticide poisoning.

In fields with trench/pond designs, the water should be drained into the trench or pond, thus driving the fish into the refuge area before the application of pesticides.

In traditional paddy field design, fish can be driven to one-half of the field and pesticide application can be done in the other half of the field. The same procedure can be repeated to the other half of the field on the following day.