Briefly describe the water requirement of rice at different growth stages.

(1) Greening period: During the rice greening period, the paddy field will maintain a certain water layer, create a relatively stable temperature and humidity environment for the seedlings, promote the early emergence of new roots and accelerate the greening. Because of the low temperature, the seedlings planted in the early days should be irrigated with shallow water during the day and deep water at night, and the seedlings should be properly irrigated with deep water to protect the cold when the cold wave comes. In case of rainy weather, shallow water or wet irrigation should be used during greening. (2) Tillering stage: The field water condition suitable for rice tillering is that the soil water content is highly saturated to shallow water to promote the early growth and rapid development of tillering. With the deepening of water layer, tillering will be inhibited. In production, the method of draining dry land is often used to inhibit ineffective tillering.

(3) Young panicle development period: The panicle development process of rice is the key period of water demand for rice life and physiology. In addition, the leakage of rice field increased after drying and rehydration, so it is generally appropriate to use water layer irrigation in this period, and the flooding depth should not exceed 10C, m, and the time to maintain deep water layer should not be too long.

(4) Heading and flowering stage: the sensitivity of heading and flowering stage to water shortage in rice fields is second only to booting stage. Water layer irrigation is generally needed. In areas where high temperature hazards are frequent during heading and flowering of mid-season rice, maintaining the water layer in rice field can obviously reduce the impact of high temperature.

(5) Water cut-off at the late filling stage will affect the absorption and transportation of rice plants and increase the number of grains. The most suitable moisture in this period is intermittent irrigation, which makes the paddy field in an alternating state of waterlogging and falling into the water.