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Alternate wetting and drying (AWD) is a management practice in irrigated lowland rice that saves water and reduces greenhouse gas (GHG) emissions while maintaining yields. The practice of AWD is defined by the periodic drying and re-flooding of the rice field.

While AWD requires a specific water regime (see The practice of AWD on the farm, below), the practice of allowing the water table to drop below the soil surface at one or multiple points during cultivation is not new. AWD and other single- or multiple- drying practices have been used for several decades as water-saving practices. About 40% of rice farmers in China practice some form of water management and short intervals of non-flooded conditions are common among rice farmers in northwestern India and in Japan (more than 80%). AWD-like practices have continued to spread.

A large potential exists for GHG reductions from rice paddies through the use of systematically introduced AWD, optimized for GHG mitigation. At present, AWD is widely accepted as the most promising practice for reducing GHG emissions from irrigated rice for its large methane reductions and multiple benefits.