**3.3 Alternate wetting and drying**

Alternating wetting and drying are the periodic drying and re-oil flooding of the rice field. Compared with mid-season drainage, the time interval between wet and dry conditions seems too short to promote the transition from aerobic soil conditions to anaerobic soil conditions [19]. Alternating wetting and drying can significantly reduce CH4 emissions, but the N2O emissions of this system vary greatly. Drainage and the resulting aerobic soil conditions will oxidize CH4 and avoid CH4 production. Song and Fujiyama [20] reported that compared with traditional flooded rice, alternating wetting and drying may reduce CH4 emissions by 73%. Yagi et al. [21] proposed that optimal irrigation according to the physiological characteristics of crops at different growth stages can limit the frequency of alternating wet and dry conditions, thereby reducing the production and emission of N2O. However, further research is needed in this practice to solve the problem of offsetting N2O emissions.
