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1. Institute of Fisheries, Chengdu Academy of Agriculture and Forestry Sciences, Wenjiang 611130, China; 2. Chengdu Seed Management Station, Chengdu 610041, China

1 Introduction

The integrated planting and breeding of paddy fields makes docking and integrated innovation of rice cultivation techniques and aquaculture techniques, in which rice and aquatic animals can get benefits from each other, greatly reducing the rice pests and diseases, using less or even no fertilizers or pesticides, greatly reducing the agricultural non-point source pollution, thus achieving the "multiple use of water, multiple harvests in one field, grain and fishing win-win, ecological and high efficient use." It not only stabilizes the "rice bag", but also enriches the "vegetable basket", which is in favor of planting and breeding cycles and agricultural sustainable development, and it is a new carrier to accelerate the transformation of agricultural development mode.

In Chengdu, there are seven kinds of integrated planting and breeding patterns in paddy fields, namely, rice-turtle, rice-shrimp, rice-loach, rice-fish, rice-crab, rice-duck-fish and rice-frog. In the whole city, the total area of paddy fields for integrated planting and breeding reached up to 3 713.3 ha in 2016, bringing about an average income increase of over 37 500 yuan/ha, and the city realized a total income increase of 140 million yuan for paddy fields from integrated planting and breeding. In this paper, the rice cultivation techniques in paddy field under rice-fish intergrowth model in Chengdu are summarized as follows.

1 Selectinggoodpaddyfieldsforfishing

The selected paddy fields for fishing should have abundant water, stable yields despite drought or excessive rain, fresh and non-polluted water sources, complete field irrigation and drainage channels, fertile soil, water and fertilizer retention capacity.

2 Usingappropriatericevarieties

The rice varieties should have fertilizer tolerance, stout sturdy stalks, resistances to lodging, strong tillering ability, strong stress resistances with rice quality achieving national second level in China, such as Chuanyou 6203, Yixiangyou 2115[1].

3 Soakingdisinfection

Before sowing, the seeds should be dried in sunny days, and then disinfected for 6-8 h by soaking in the 2 500-3 000 times diluted 25% prochloraz (Shibaike) emulsifiable concentrate (EC) + 1 500 times diluted 3% metalaxyl hymexazol (Guangkuling) aqueous solution. After cleaning and drying, the seeds are coated using "drought-foster nurse" (0.5 kg for 2.0 kg of seeds), so as to improve the seed germination rate and enhance seedling disease resistance[2].

4 Timelysowing, andnurturingstrongseedlings

In Chengdu area, the seeds should be sown in late March or early April, and the seedlings age should be 30 d for transplanting. It should adhere to the principle of thin sowing and evenly transplanting with the appropriate seeding rate of 150.0-187.5 kg/ha. Before sowing, it should apply with enough base fertilizers. Generally, 750 kg/ha of compound fertilizer is applied as the base fertilizer, and 90-120 kg/ha of urea is applied for topdressing at 4-5 d before transplanting. The fertilizers are applied with pesticides. Before transplanting, the seedlings have 2-3 tillers[3].

5 Reasonablecloseplanting

The seedlings should be transplanted from the end of April to the end of May. If conditions permit, the transplanting should be completed as early as possible to increase the intergrowth period for field fish and field duck in the paddy field. For the breeding of aquatic animals with small sizes such as fish, shrimp, crab and loach, wide row and short space between plants is adopted with the transplanting specifications of 16.7 cm × 33.3 cm; in the case of breeding the animals with large sizes such as soft-shelled turtles, ducks, wide and narrow row spacing is adopted with the specifications of 16.7 cm × (20.0 cm + 40.0 cm). The seedlings are planted in east-west direction, which is favorable for the growth of Oryzias latipes and increasing the permeability. In the mean time, the planting density on both sides of the fish ditch should be increased to give full play to the marginal advantage. Generally, there are 135 000-150 000 holes/ha, and each hole is planted with 5-7 rice seedlings to ensure that there are 900 000-1 200 000 basic seedlings per hectare. The high yield seedling frame should be well built[4].

6 Reasonablefertilization

Fertilization of paddy fields for fish farming should adhere to the principle of "organic fertilizer-oriented, inorganic fertilizer-assisted heavy basal fertilizers and light topdressing", and the total amount of fertilization should be reduced by more than 30% as compared with that of conventional paddy rice. The application of basal fertilizer for the paddy field should be considered according to soil fertility, and the general application of organic fertilizer is 4 500-6 000 kg/ha or composting manure of 6 000-9 000 kg/ha. Topdressing is conducted according to the fertilization in early stage and the seedlings growth conditions in the paddy fields, and compound fertilizer is the best one as topdressing. Attention should be paid to the fertilization methods. Urea of 45-65 kg/ha is used as the fertilization for head sprouting, and no application for the seedlings with green leaves. Before and after the field drying, potash of 150-225 kg/ha can be applied to strengthen the stalks and grains, prevent rice lodging.

7 Scientificwatermanagement

It should properly handle the direct contradiction between rice and fish, and adjust the water level timely according to the characteristics of rice at different growth stages. At the early growth stage of rice seedlings, the water in the paddy field should be low for transplanting and fresh for striking roots. After that, the water depth should be controlled at 6-8 cm to promote rice tillering. Continuous sunny days are preferred for paddy field drying, and the water level should maintain at 10 cm lower than the ridge surface. After field drying, the water level can be deepened to 15-18 cm, to satisfy the needs for the activity and growth of field fish. At 10-15 d before rice harvest, the field water level should be lowered, and the best depth is the water level in the fish ditch is 10 cm lower than the filed water level to make the fish live in the fish ditch, so as to carry out rice machinery harvesting.

8 Scientificpreventionandcontrolofpestsanddiseases

Pest control should adhere to the principle of "prevention-oriented comprehensive control", set trap light and sex attractants reasonably and adopt green control measures to prevent and control rice pests and diseases. If pesticides are indeed needed, the biological pesticides which are fitted, high-efficient, low toxic and low residual are preferred, highly toxic pesticides on fish species are strictly prohibited[5]. As for the formulations of pesticides, aqueous solution or oil solution of pesticides should be preferred, while no or little powder is advocated, and the paddy field for fish breeding should use no herbicides. During the pesticide application, the water depth can be deepened, and water inflow and outflow are conducted at the same time to reduce the concentration of pesticides in water. Aqueous solution (emulsion) pesticides should be used after dew drying. When spraying the pesticides, nozzles should be horizontal or up to make the pesticides spray to the rice seedlings to the greatest extent and reduce the chance of falling in the water. Do not spray pesticides before raining or thunderstorm, otherwise pesticides will be washed into the fields by rainwater, which will not only result in poor control but also lead to fish poisoning.

9 Riceharvest

At 10-15 d before rice harvesting, the water level in the fish ditch has already 10 cm lower than the field surface, which is convenient for the mechanical harvest of rice. After harvesting rice, if the field fish have reached the market specifications, they should be timely caught for sales; if they fail to meet the listing requirements, the breeding can continue by deepening the water level in the paddy fields. The households with supporting ponds can transfer the fish into pond for continuous breeding, or can combine with the low-lying winter free fields to extend the time to market aquatic products, which can come into the market avoiding the peak hour[6].

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