Raising Crab in Paddy Field: ecological Regulation is the key

Raising crabs in rice fields is an ecological breeding model that has sprung up in recent years. Raising crabs in rice fields can not only remove weeds in rice fields, make rice fields have sufficient light, but also prevent rice pests and reduce the use of pesticides and fertilizers, which not only ensures the high-quality ecology of rice, but also ensures the quality and safety of river crabs, and realizes the win-win situation of planting and breeding. The technique of raising crab in rice field is simple and the benefit of raising crab is good. Today, I will introduce to you a set of techniques for raising crabs in rice fields for farmers' reference.

1. Rice field facilities construction   

Raising crabs in rice fields can yield more than 450 kg of rice and 10 kg of crabs per mu. Crab-raised rice fields are required to choose mid-maturing late japonica or hybrid japonica fields with sufficient water source, good water quality, convenient drainage and irrigation, strong water retention and fertile soil, or retting fields that are not dehydrated all the year round. The ridge around the crab paddy field should be strengthened, which is 66 centimeters high and the soil should be compacted to prevent water leakage from escaping crabs. The Fudui River is excavated around the field, and the ridge of the river is 2cm. The river is 3 meters wide and 1.5 meters deep, with a slope ratio of 1 ∶ 2. Crab trenches should be dug in the middle of larger fields, with a width and depth of 50 cm, which can be shaped like "day", "field", "encirclement" and so on, accounting for 10% to 15% of the total area.  

In order to raise crabs in rice fields, it is necessary to build fence anti-escape facilities and inlet and outlet anti-escape facilities. One is to build a calcium plastic board anti-escape wall. The calcium-plastic board with strong anti-oxygen ability can be selected along the fence around the field block, the board is buried in the soil 10 to 20 centimeters, about 50 centimeters higher than the ground, the outside is supported by wooden piles, and the two calcium-plastic plates are tightly connected with fine wire, and the four corners are made into a circular arc. This kind of anti-escape wall has the advantages of convenient transportation and installation, low cost and good effect, and can be used for 2 to 3 years.

Second, Luchaibo and plastic film (or linoleum) structure anti-escape wall. The quality is better, 80cm 100cm wide Reed foil is buried under the soil around the field block about 5cm, the outside is fixed with a wooden pile every 2m, the wooden pile is fixed into the soil more than 15cm, the inside is fixed on the firewood foil with thin iron wire, the film (or linoleum) is embedded in 2cm, and 48 cm is unearthed, the whole escape wall end can be tilted inward. The cost of this kind of anti-escape wall is very low, but it is not very wind-resistant, so it should be repaired and replaced in time, and its service life is generally only 1-2 years. It can also directly fix the wooden pile fence with double-layer film or linoleum to prevent escape, and its effect is poor.   

The third is the setting of the inlet and outlet. According to the migratory habits of crabs, in order to facilitate crab fishing, the intake is best located in the northwest or west of the field, and the outlet is located in the southeast or east. The foundation of the inlet and outlet should be tamped. After laying a layer of flat brick, the cement pipe with a diameter of 40 cm is installed and made of cement sand and gravel. There should be no gap between them, and the inlet had better be curved. The inlet and drain should be sealed with polyethylene mesh, and a bamboo grid should be built and covered with a net to prevent crabs from escaping from the inlet and drain.   

2.   of paddy field water quality regulation.

The suitable rice varieties are Shanyou 63, Nanyou 6, Liuyou 1, Wuyujing 3, Yanjing 187 and Yanjing 235.  

It is necessary to apply sufficient basic fertilizer to raise crab in rice field before seedling transplanting. Organic fertilizer is better than cake fertilizer, which has long time effect and good effect. Generally, 250 kilograms of human feces and urine and 150 kilograms of cake fertilizer can be applied per mu, and inorganic fertilizers can also be used in areas lacking organic fertilizer. the total application rate is suitable to basically ensure the growth needs of rice during the whole growth period.  

Two or three days before transplanting, a high-efficiency pesticide was applied to the seedlings to prevent the spread and spread of rice diseases and insect pests. Transplanting in shallow water and planting with wide rows and dense plants are usually used to give full play to marginal advantages and improve rice yield. Within a week after the seedlings are planted, especially before the seedlings turn green, it is necessary to reduce the entry of crabs into the seedling field as far as possible so as not to affect the survival of the seedlings.

Water quality regulation the dissolved oxygen in the rice field water of crab culture generally needs to be kept above 5 mg per liter and the pH value is 7.5-8.5. The water level in the field was about 20 cm when the seedlings were transplanted into the field, and then gradually increased to 60 cm with the increase of water temperature and the growth of seedlings. The water should be changed every 7-15 days after May, and every 2-3 days in the high temperature season, about 20 cm each time. When changing water, it should be noted that the water temperature difference inside and outside the field should not exceed 3 ℃ ~ 5 ℃, and avoid changing water during the crab latent rest and the best feeding period.  

Rice field management crab paddy fields usually only apply topdressing twice in the whole year, with about 2.5 kilograms of urea per mu each time.

3. Seedling stocking specification  

About a month before clearing the field and disinfecting seedlings, drain the water in the Fudui River and crab ditch, expose it for a few days, then release water 5cm to 10cm, melt it with 75kg of quicklime per mu and sprinkle it all over the pond without cooling. Before releasing the crab, you should also temporarily raise the fish to test the water to see if the medicine has completely disappeared.

From February to April, when the water temperature reaches 5 ℃ ~ 10 ℃, choose a sunny day and put the crabs into the Fudui River. To cultivate young crabs in rice fields, crab seedlings are usually released into Fudui River from May to June (rice fields are not suitable for mixed culture of fish and crabs).

Specification and density of rice fields to grow crabs is generally appropriate to breed 150 crabs per kilogram. The stocking density should be controlled flexibly according to the situation of the paddy field, and it is appropriate to put 2.5 kilograms per mu. It is best to breed crab species of the same specification in the same field. When crab species of different specifications are mixed, feed must be very adequate. It is also possible to raise a small amount of silver carp and bighead carp in fields where it is difficult to regulate water quality. generally, about 1 kilogram of silver carp and bighead carp larvae are released in Fudui River per mu. It is appropriate to put about 250 grams of bigeye larvae per mu to cultivate young crabs in rice fields.   

4. Daily feeding management   

In the field where the young crabs are fed with bait, fertilize the water first and then release the seedlings. After the crabs are put into the field, they are fed with soy milk or egg yolk once or twice a day and sprinkled evenly. After a week, gradually change to paste feed, such as bean cake paste, vegetable cake paste, wheat bran paste, pumpkin paste, sweet potato paste and some animal viscera chopped paste, and feed a sufficient amount of aquatic plants, and add appropriate amount of molting to the feed during molting.  

According to the 50 grams of crab species, the fields cultivated for adult crabs are put 50 grams and 100 kilograms of live snails into the repile ditch to let them lay eggs and breed for crabs to eat, and properly feed some soaked or cooked wheat, corn and other plant bait, and add some green duckweed. The period from July to October is the peak period for crab growth. The feed should be adequate, nutritious, fresh and pollution-free, and sufficient animal and plant bait should be fed, such as snail meat, clam meat, silkworm pupa, fish and shrimp, animal carcasses, slaughtering leftovers and aquatic plants, wheat, cereals, cakes and so on. Before and after crab molting, molting element should be added to the feed, and some calcium-rich baits such as eggshell powder, bone powder and shrimp shell powder can also be fed appropriately. After November, the water temperature decreases gradually, so the amount of bait can be reduced. The daily feeding amount should be flexibly controlled according to the water temperature and the crab's food intake on the previous day, which is generally 5% or 10% of the crab's body weight. The baiting times are 2 times a day, feeding 1x3 at 6: 8 am and 2 at 6 pm. It is better to feed on the shallow water slope of the ditch river. Feeding should be "timing, positioning, quality, quantitative".   

Daily management is mainly field inspection, once a day in the morning and evening, to check whether the escape prevention facilities are damaged, whether the drainage channel is leaking, to observe the crab's feeding, molting and growth, and to remove suitable and rotten residual bait in time.   

At present, the disease prevention and control of crab in rice field is less, generally focusing on prevention. 2000 international units of malachite green solution is used to bathe the crab during stocking. During the breeding period, 15,25kg quicklime per mu was sprinkled once a month in the Fudui River and crab ditch, and regularly mixed with oxytetracycline in the bait. There are water rats, water snakes, frogs and water birds that do great harm to crab farming in rice fields. Many methods can be used to remove them, such as putting rat poison, placing rat cages, rat traps, "scarecrows" and artificial hunting and killing.