Three key stages to grasp in rice film seedling raising
Based on many years of practical experience, I believe that three key stages should be noted in the technique of raising rice seedlings under film: the closed stage, the hardening stage and the film-removal stage.
The first stage: the closed stage, that is, from sowing to the one-leaf-one-heart stage. During this period the film must be tightly closed to create conditions of high temperature and high humidity inside the film and promote the rice seeds to root quickly and establish seedlings. The temperature inside the film should be controlled at 30-35°C. If it exceeds 35°C, promptly open both ends of the film at noon for ventilation and cooling to prevent the seedlings from being “scorched”; cover the film again around four in the afternoon to maintain a suitable temperature. If it is below 30°C, keep the film sealed all day and fill the side ditches outside the film with water at noon to preserve or raise the temperature and prevent the seedlings from being damaged by cold. The relative humidity inside the film is best kept at 85-95%.
The second stage: the hardening stage, that is, from one-leaf-one-heart to two-leaf-one-heart. Use 4-5 days for hardening, adopting the gradual method of “open both ends - open windows at the front and back (left and right) - uncover one side - uncover by day and cover at night - finally uncover completely” to harden the seedlings, gradually adapting them from the environment inside the film to the climate outside. At the same time, take care to keep the seedbed moist to prevent the seedlings from wilting or even dying due to physiological water loss.
The third stage: the film-removal stage, that is, from two-leaf-one-heart to the three-leaf stage. Through hardening, the seedlings have already adapted to the natural climate environment; when they grow to about 10 cm and the temperature stabilizes above 13°C, irrigate and completely remove the film. Irrigation should generally be just enough to keep the seedbed moist, which helps cultivate strong seedlings (if low or high temperatures suddenly occur, flooding irrigation may be used so that the seedlings are not burned by high temperatures or damaged by low temperatures).