Rice and shrimp symbiotic technology
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**Crayfish Breeding in Rice Fields: A Sustainable Agricultural Model**
The practice of raising freshwater crayfish in rice fields is an innovative agricultural model that combines rice cultivation with aquaculture. This system takes advantage of the shallow water environment in rice paddies, supplemented by human management, to grow both rice and shrimp together. The principle behind this symbiotic approach is mutual benefit, where waste from one process becomes a resource for another, creating a balanced ecosystem that is environmentally friendly. In practical terms, this method is often referred to as "rice farming in rice fields, and shrimp farming in rice."
**Field Construction**
1. **Selection of Paddy Fields**
- **Water Source**: The water supply must be abundant, clean, and easy to manage through irrigation and drainage systems. Adequate infrastructure for water control is essential.
- **Soil Quality**: The soil should be fertile, ideally composed of clay or loam, which retains moisture and nutrients well.
- **Area**: A minimum of 10 acres is recommended, though larger areas are more efficient. The ideal size allows for better water circulation and easier management.
2. **Excavation of Ditches**
- A circular ditch is typically dug around the paddy field. For larger fields, additional ditches in the shape of “tian†(heaven), “chuan†(stream), or “well†can be added.
- The ring ditch should be about 3 meters away from the edge, with a top width of 4–6 meters, a bottom width of 1–1.5 meters, and a depth of 1.2–1.5 meters.
- Field ditches are narrower, around 1.5 meters wide and 0.5–0.8 meters deep. These ditches occupy roughly 20% of the total field area.
3. **Ridge Reinforcement**
- Earth from the ditches is used to build raised ridges, which should be 1.2–1.5 meters high and at least 3 meters wide. The ridges must be compacted tightly to prevent leaks or cracks.
4. **Escape Prevention Facilities**
- One common method involves installing high-density plastic boards, 55 cm tall, buried 15–20 cm into the ridge and secured every 75–100 cm. Corners should be rounded to prevent crabs from climbing.
- Another option is using a combination of mesh and hard plastic film. A dense mesh 1.2–1.5 meters high is placed around the field, with a 25–30 cm wide plastic strip sewn on top, 10 cm above the mesh.
- Inlet and outlet pipes should have double-layer fine nets to prevent escape and contamination. An overflow outlet with a net filter is also necessary to avoid damage during heavy rains.
5. **Preparation Before Stocking**
- Before introducing crayfish, the ditches are cleaned and disinfected using substances like rotenone, tea alum, quicklime, or bleaching powder to eliminate predators and parasites.
- Aquatic plants such as Hydrilla verticillata, Vallisneria, and water peanuts are planted in the ditches, while floating plants like water hyacinth and duckweed are placed on the surface.
- Organic fertilizers like chicken or pig manure are applied one week before planting to enrich the water and support natural food sources for the crayfish.
**Rice Cultivation Techniques**
1. **Rice Variety Selection**
- Single-season rice varieties with small leaf angles, strong disease resistance, and good lodging resistance are preferred. Popular choices include Xie You series and other high-yield strains.
2. **Base Fertilization**
- Apply 200–300 kg of farmyard manure per acre, along with 10–15 kg of urea. Mix thoroughly with a plow to ensure even distribution.
3. **Seedling Transplanting**
- Transplanting usually begins in mid-June. A combination of strip and side planting methods is used. A spacing of 30 cm x 5 cm is recommended to promote air circulation and reduce overcrowding.
**Crayfish Stocking**
1. **Preparation Before Stocking**
- Clean the ditches 10–15 days before stocking, remove debris, and treat them with lime or other disinfectants to kill unwanted fish and pathogens.
- Fill the field with 30–50 cm of water 7–10 days before stocking, and apply livestock manure to enrich the water. Plant aquatic plants in half of the ditch area to create a favorable habitat.
2. **Planting Aquatic Plants**
- Submerged plants like Hydrilla verticillata and Ceratophyllum deliciosum are placed in the ditches, while floating plants cover the surface. The coverage should be limited to 40–50% of the ditch area to maintain water flow.
3. **Stocking Time**
- Early stocking is encouraged to maximize growth periods and utilize natural food sources. Ideal times are late August to September or early March of the following year.
4. **Stocking Density**
- Stock 20–25 kg of broodstock per mu, with a male-to-female ratio of 3:1. Juvenile shrimps can be stocked at 0.8–1 million per acre. Broodstock should be kept in outer ditches during winter and released when the rice turns green.
5. **Stocking Procedures**
- Choose cool, cloudy days for stocking. Distribute seedlings evenly around the ditches to avoid over-concentration. Ensure consistent quality and size of the stock.
**Water Level Management**
- Water levels should be adjusted based on rice growth stages. Initially, keep the water shallow (around 10 cm), then gradually increase it to 20–25 cm as rice grows. Maintain shallow irrigation during tillering and deeper water after that to support both crops.
**Feeding Management**
- Natural feed like Cladocera, copepods, and snails are cultivated through base fertilization. Artificial feeds should be split 40% animal-based and 60% plant-based. Feed in the morning, afternoon, and evening, adjusting amounts based on consumption rates.
**Fertilization Practices**
- Use decomposed manure and base fertilizers to support rice growth without harming crayfish. Avoid chemical fertilizers that could reduce oxygen levels. Apply 300 kg of manure, 20 kg urea, 20 kg superphosphate, and 5 kg potassium sulfate per acre.
**Pest Control**
- Minimize pesticide use. If necessary, choose low-toxicity options and spray in the morning or afternoon. Avoid direct application into water and consider drying the field temporarily to reduce exposure.
**Field Drying**
- Dry the field lightly before harvest, keeping water levels in ditches at 13–17 cm. Avoid long drying periods to prevent stress on the crayfish.
**Disease Prevention**
- Focus on prevention rather than treatment. Remove predators like snakes and birds, and install scarecrows if needed. Avoid feeding ducks in the ditches to reduce losses.
**Additional Management**
- Regular field inspections are crucial. Monitor water quality, check for leaks, and maintain ditches. Keep records of all activities and address issues promptly.
**Harvesting**
- Rice is harvested first, followed by raising water levels to encourage crayfish movement. Shrimp are typically caught between April and September using traps.
This integrated approach not only maximizes land use but also promotes ecological balance, making it a sustainable and profitable farming method.