Key Technical Points for Cultivating Strong Seedlings in Rice Tray Nursing for Machine Transplanting

Economic Daily News: Raising small strong seedlings of tray-nursed machine-transplanted rice is an important part of achieving high quality and high yield in machine-transplanted rice. The specific technical points are introduced as follows:

Tray Soil Preparation

Select loam soil that is fertile, free of stubble, gravel, weeds, and free of contamination to seedlings, with a pH value of 4.5-5.5. If such acidic soil is not available, sulfuric acid or nitro humic acid can be used to adjust the acidity. To prevent damping-off and other seedling-stage diseases, apply 50-60 grams of dexon per cubic meter of tray soil. To fertilize the tray soil, add 200-400 grams each of pure nitrogen, pure phosphorus, and pure potassium per cubic meter of tray soil, mix thoroughly and sun-dry, then sieve through a sieve with an aperture of 4-6 millimeters. Each mu of net seedling bed area requires 20 cubic meters of dry fine nutrient soil.

Seed Treatment

Select varieties with high purity, removed awns and branch stalks, a germination rate above 90%, strong germination vigor, and a panicle-grain combined type. For wheat-stubble rice, early-maturing medium japonica, medium-maturing medium japonica, or medium indica are more suitable. Sun the seeds on a sunny day for 2-3 days, use the mud slurry or salt water seed selection method to remove empty and shriveled grains. Dilute 25% prochloraz emulsifiable concentrate 2000-3000 times, soak the seeds for 48-60 hours, then rinse with clean water, and germinate until the seeds break through the hull and show white, then they can be sown.

Seedling Bed Requirements

The seedling bed should be close to the main field to facilitate transporting seedlings and improve work efficiency. The ratio of net seedling bed to main field is about 1:160. The soil should be fertile, with convenient drainage and irrigation, and ground levelness with a height difference not exceeding 3 cm. The bed surface width is 1.4 m, the ditch width is 0.25-0.3 m, and the softness and firmness should be such that feet do not sink and the surface does not turn white. Place 2 trays of 1.2 m width horizontally on each bed surface, leaving 10 cm on each side of the bed. When placing trays, ensure the trays are flat and adhere to the mud, with no gaps between trays. Set up a frame over the bed surface and cover with film.

Mechanical Sowing

Mechanical sowing can complete soil loading, water spraying, seed scattering, and soil covering in one pass, with high sowing efficiency and good sowing quality. Before sowing, appropriately air-dry the pre-germinated seeds or place them in a gauze bag and spin them in an electric spin dryer for 1-2 minutes, until they are suitable for sowing without sticking to the hands. The bottom soil in the sowing tray should be 2 cm thick, and the covering soil should be 0.5-1 cm. The tray soil should be sprayed with water to a moist state. Sow about 0.2 kg of germinated grains per tray, scattering the seeds evenly.

Seedling Bed Management

Before the 1-leaf 1-heart stage, keep the tray surface soil moist, with the temperature controlled at 30°C. At this time, if seedling leaves lift the soil, spray washing can be used. After 1.5 leaves, control the daytime temperature at 20-25°C, and the nighttime temperature at about 15°C, with the ditch water preferably not exceeding the tray surface. After 2.0 leaves, allow the bed temperature to gradually approach natural temperature. Drain the ditch water 2-3 days before transplanting to promote root binding of the seedlings, facilitating seedling lifting and machine transplanting.

Scientific Fertilization

At the 1-leaf 1-heart stage of the seedlings, apply 0.5-1 gram of urea per tray (tray inner diameter 58 cm × 28 cm). 3-4 days before the seedlings leave the bed, apply 1.2-1.5 grams of urea per tray, which benefits the normal growth and development needs of rice and facilitates rapid greening and establishment after machine transplanting.

Disease and Pest Control

At the same time as applying the departure fertilizer, spray each mu of seedling bed with 75 grams of 20% tricyclazole wettable powder plus 100 mg of 50% methamidophos emulsifiable concentrate or 200 mg of 18% dimehypo aqueous solution, mixed with 50 kg of water, to prevent rice blast, rice thrips, and other diseases and pests from being brought into the main field.

Timely Machine Transplanting

When the seedlings have 2.5-3.5 leaves and a seedling height of 12-15 cm, machine transplanting should be carried out promptly. After exceeding 3.5 leaves, seedling quality begins to decline, and the seedling stagnation period after transplanting is long, which is not conducive to early development.