Rice seedling raising is key: good seedlings mean half the rice is already grown, and strong seedlings lead to high yields.

Seedling-stage management for machine transplanting is key. Cultivating robust seedlings suitable for machine transplanting is the key to the success of promoting mechanized rice transplanting. "Good seedlings mean half the rice is grown, and strong seedlings lead to high yields." The quality of the seedlings plays an important role in the number of panicles, number of grains and grain weight in the later growth stages of rice. The basic requirements of mechanized transplanting for seedlings are overall uniformity and individual robustness, requiring that "a tray of seedlings has no tall and short ones, and a handful of seedlings has no thick and thin ones."

High temperature and high humidity promote uniform emergence.

Germinated rice seeds, after sowing, need to go through a period of high temperature and high humidity for seedling establishment to ensure uniform emergence. Therefore, according to the different seedling-raising methods and crop rotations, corresponding measures to increase temperature and retain moisture should be taken to ensure safe and uniform emergence. At the same time, the seedling field should have a level-water gap opened well to avoid rainfall flooding the seedling bed, which causes sealed seeds and rotten sprouts.

Sealing with film and covering with straw for seedling establishment. Sealing with film and covering with straw for seedling establishment is suitable for raising seedlings of wheat-stubble rice when the temperature is relatively high. It includes three types: double-film seedling raising, manual sowing in soft trays, and machine sowing with direct tray removal. During the seedling establishment period, two points should be noted: first, control the thickness of the straw cover, keeping it uniform to avoid burning seedlings from high temperatures at noon on sunny days. Second, promptly remove accumulated water on the covering film after rain, to avoid water accumulation on the film surface and, together with the added weight of the soaked straw cover, local pressure causing a "plaster-like" effect, resulting in sealed seeds and rotten sprouts and affecting full stand.

Arch shed seedling establishment. Arch shed seedling establishment is suitable for early spring seedling raising when the temperature is relatively low and for areas prone to late spring cold. With this method, after the young shoots emerge above the soil surface, the surface temperature inside the shed at noon on sunny days should be controlled below 35°C to prevent high temperatures from scorching the young seedlings.

The period from sowing to emergence is generally the stage when the shed film is kept sealed, mainly for heat preservation and moisture retention. Only when the temperature inside the film exceeds 35°C should the two ends of the seedling bed be opened at noon for ventilation and cooling, and then promptly sealed again. During this period, if the bed soil turns white and the seedling leaves curl, "running horse water" should be irrigated to retain moisture.

Harden seedlings in time.

Remove the film to harden seedlings. The film covering time should not be too long. The time for removing the film depends on the temperature at the time. Generally, the film is removed to harden seedlings when the seedlings have emerged about 2 cm and the incomplete leaf to the first leaf has unfolded (3-5 days after transplanting). If the covering time is too long, exposure to strong sunlight and high temperatures can easily scorch the young seedlings. Principles for removing the film: remove in the evening on sunny days, in the morning on cloudy days, before light rain, and after heavy rain. If a cold wave with low temperature occurs, it is advisable to postpone film removal and to remove it by day and cover it at night.

Hardening seedlings in arch sheds. After the seedlings turn green, determine the time to dismantle the shed according to temperature conditions. The shed can be dismantled only when the minimum temperature is stable above 15°C; otherwise, the method of removing by day and covering at night can be used for management, and the tray soil (or bed soil) should be kept moist.

Scientific water management.

Moisture management. That is, adopt intermittent irrigation, mainly keeping moist, to achieve the goals of regulating air with water, regulating fertilizer with water, regulating temperature with water, and protecting seedlings with water.

Key operation points: when removing the film, irrigate level ditch water, then add water again after it naturally drains dry, and repeat this process. If seedling leaves curl at noon on sunny days, irrigate thin water to protect the seedlings; on rainy days, drain the ditch water in the seedling field. If early spring seedlings encounter a strong cold air invasion, irrigate waist-high water to protect the seedlings; after it warms up and the temperature stabilizes, change the water to protect the seedlings, preventing root damage from low temperatures and seedling rot and death caused by excessive temperature differences. After the temperature returns to normal, drain and aerate in time to improve root activity of the seedlings. Control water to harden seedlings 3-5 days before transplanting.

Water-control management. This is basically similar to the water management technique for conventional dry seedling raising in fertile beds, that is, irrigate enough water once when removing the film (level ditch water), and drain after the bed soil is thoroughly soaked (spraying to supplement water may also be used). At the same time, clear the seedling ditches and keep the water system unobstructed to ensure there is no standing water in the seedling field on rainy days, preventing dry-raised seedlings from being flooded and losing the advantages of dry raising. Afterward, if the seedling leaves curl at noon, spray water manually once in the evening or early the next morning, just enough to moisten the soil. If the leaves do not curl, do not supplement water. The water used for supplementation must be clean, otherwise it can easily cause seedling death.

Make good use of "weaning fertilizer."

The application of weaning fertilizer should be carried out according to local conditions based on the fertility of the bed soil, seedling age and temperature. It is generally applied at the one-leaf-one-heart stage (7-8 days after sowing). For each mu of seedling pond field, use 500 kg of decomposed manure liquid mixed with 1000 kg of water, or 5 kg of urea (about 2 grams of urea per tray) mixed with 500 kg of water, and apply it in the evening when the seedling leaves are exuding water. If the bed soil is fertile, it may not be applied. In wheat-stubble fields, to prevent the seedlings from growing too tall, the fertilizer amount can be appropriately reduced.

Coping with late spring cold during the seedling stage.

Deep water protects seedlings, regulating temperature with water and regulating air with water. When low temperature and a cold wave occur, irrigate deep water to the seedling fork to protect the seedlings, but be careful not to submerge the seedling heart. After the cold wave, if the weather suddenly clears, do not immediately drain the water to dry the field, to avoid causing bacterial wilt, seedling rot and seedling death. The main danger of late spring cold lies in the sudden clearing of weather and the abrupt rise in temperature, which causes physiological dehydration of the seedlings. A deep water layer can alleviate drastic changes in the seedling bed temperature.

Promptly splash-apply Dexon. Before low temperatures arrive or after a cold wave, 100-150 grams of Dexon per mu of seedling field can be diluted into a 1000-fold solution and splash-applied to prevent seedling rot and death. After prolonged cloudy, rainy and low-temperature weather, Zhuangyangbao should be sprayed in time to prevent the occurrence of damping-off disease.

Arch shed freeze protection. If the temperature drop is large and lasts a long time, where conditions permit, the above two measures can be combined with building an arch shed to preserve heat and prevent freezing.

Avoid topdressing too early. After low temperatures, the stress resistance of the seedlings is relatively poor. If chemical fertilizer is applied too early, for the weakly growing seedlings it is like adding frost to snow and accelerates seedling rot and death. Therefore, topdressing should be carried out 3-4 days after the low temperature ends.