The Latest Guide to Rice Seedling-Stage Management Techniques and Methods
Seedbed Temperature Management
1. From sowing until the first leaf tip emerges, focus on heat preservation. Keep the temperature inside the shed at 28-30°C, with the optimum at 25-28°C; maintain 25°C at the 2-leaf stage and 20-22°C at the 3-leaf stage, with the minimum not lower than 10°C. Night temperatures are low, so measures such as turning on electric lights inside the greenhouse or burning rice husks should be taken to raise the temperature. For small-shed seedling raising, measures such as covering the outside of the shed with rice straw or cold-proof quilts should be taken to raise the temperature, ensuring the minimum temperature indicators required for each leaf age of the seedlings are reached, so that the rice seeds can grow and develop normally on the seedbed.
2. Seedbed ventilation management. After the rice seedlings emerge and turn green, the plastic film should be removed, preferably in the morning or evening, when the temperature difference inside and outside the shed is small and the seedlings adapt to the new environment quickly. If the film is removed at midday when the temperature is high, the aboveground seedlings transpire quickly while the roots absorb slowly, which easily causes physiological water loss in the seedlings. After removing the film, light ventilation can begin. When ventilation reaches the minimum temperature limit for each leaf age, the shed should be closed promptly. As leaf age increases, the ventilation hardening time should be extended accordingly, especially at the 2.5-leaf stage, when the temperature must not exceed 25°C; if it is higher than 25°C, ventilate to cool down to prevent early heading. After the 3-leaf stage, gradually increase ventilation so that the temperatures inside and outside the shed are nearly the same. If there is no frost at night, there is no need to cover with film; just wait for transplanting.
Seedbed Moisture Management
1. When the bottom water has been thoroughly watered, in principle try not to water before the 2-leaf stage. Afterwards, watering the seedbed should follow the three observations: first, observe whether there are dew drops on the leaf tips in the morning and evening; second, observe whether the newly unfolded leaves curl at midday when the temperature is high; third, observe whether the surface of the seedbed soil turns white. If the leaves do not exude water in the morning and evening, the newly unfolded leaves curl at midday, and the seedbed soil surface turns white, water thoroughly and fully in one go with water warmed by the morning sun, minimize the number of waterings, and do not irrigate the bed with cold water, which can cause cold-water seedling stiffness and affect the growth and development of the rice seedlings.
2. As far as possible, achieve dry raising for strong seedlings: water grows shoots, while dry conditions grow roots. To get good root binding in the seedlings, seedbed moisture must be controlled. Only under dry-raising conditions can the root system development of the seedlings be promoted. Especially 2-3 days before transplanting, it is best not to water, so that the seedling roots remain under dry raising. If the seedlings do not bind roots well before transplanting, apply root-promoting agent by drenching 1-2 days before transplanting, which can make rice seedlings produce more roots, more white roots, and longer roots, with good root binding.
Controlling Seedling Spindling, Dwarfing and Promoting Tillering
The key to cultivating strong seedlings is controlling spindling. Paclobutrazol has the effect of inhibiting seedling elongation and promoting tillering; it can increase the chlorophyll content of seedlings, enhance enzyme activity, facilitate metabolism, and strengthen drought and cold resistance. Practice has shown that spraying 15 days after emergence, using 0.2-0.3 grams of 15% paclobutrazol per square meter mixed with Jiumiao seaweed acid iodine, gives good dwarfing and tillering promotion results. Standards for strong seedlings: seedling age 30-35 days, leaf age 3-3.5 leaves, seedling height 12-14 cm, 9-11 roots per seedling, stem thickness 2.5-3 mm, dry weight of 100 plants 3-3.5 grams, and tillering rate above 30%.
Preventing Rice Seedling-Stage Damping-Off and Bacterial Wilt
Based on the alternating cold and hot weather conditions in late April, seedling-stage diseases are prone to occur.
1. Rice damping-off is mainly caused by multiple factors such as low temperature and high humidity, large temperature differences, alkaline soil, insufficient light, excessive sowing rate, and thin and weak seedlings. It seriously affects the improvement of rice seedling quality and rice yield per unit area, so comprehensive prevention and control measures based on prevention must be taken to prevent the occurrence and spread of rice damping-off.
2. Damping-off is a fungal disease and can be divided into three types according to the period of onset: bud rot, basal rot, and yellow blight. Bacterial wilt is a physiological disease, mostly occurring after the 3-leaf stage, with leaves turning green, no water droplets at the leaf tips, rolling, and the central leaf in a tube shape; in severe cases, the entire rice seedling dies.
3. Control methods
(1) Control of damping-off. Do a good job of seed and seedbed soil disinfection, control the temperature and humidity of the seedbed well, cultivate strong seedlings, and improve disease resistance of the seedlings. When damping-off occurs in seedlings, spray with Likukexing mixed with Jiumiao seaweed acid iodine, which can effectively control damping-off.
(2) Control of bacterial wilt. Reduce the sowing rate and advocate the use of isolation-layer seedling raising, which can increase ground temperature. During ventilation hardening, attention should be paid to blocking below the shed opening with woven fabric and similar materials to avoid strong wind directly causing bacterial wilt. When the disease is relatively severe, irrigate water onto the bed, and immediately drain the water after the leaves unfold. In severe cases, use Ruimiaoqing aqueous solution, spraying 1 milliliter per square meter, to cure it.
Before Transplanting, Achieve the “Three Carries” and Implement Health-Building Cultivation
Before transplanting, the “three carries” work for seedlings should be done well. The first is carrying soil, which can ensure transplanting quality and help seedlings quickly turn green and survive. The second is carrying fertilizer: apply 150 grams of diammonium phosphate per square meter of seedbed, then water to wash the seedlings, which can promote root development. The third is carrying pesticide: for every 100 square meters of seedbed, use 4 grams of Aimeile diluted with water to spray the seedbed to prevent leafminer, and at the same time spray 75% tricyclazole or Tianfengsu 1500-fold solution for health-building cultivation. Advocate early land preparation and early transplanting. Transplanting 1 day earlier can capture more than 20°C of active accumulated temperature, which helps rice mature before frost.