Alternate Wetting and Drying

1. A perforated field water tube is installed so the water level below the soil surface can be observed
2. The paddy is flooded as usual, then irrigation is withheld and the field allowed to dry
3. The water level in the tube falls as water is used and drains away
4. When the level drops to a defined safe threshold, the field is re-flooded
5. The wet–dry cycle is repeated through the season, with continuous flooding kept around sensitive stages such as flowering

Continuous flooding keeps paddy soils saturated and largely without oxygen, which favours the microbes that produce methane and means water is continually lost to seepage, percolation, and evaporation. By letting the soil dry and aerate periodically, AWD reduces the volume of irrigation water applied and interrupts the conditions that generate methane, which is why it is promoted as a climate-smart rice practice.

AWD is described as "safe" when the field is re-flooded before the water level falls far enough to stress the crop, and when continuous flooding is maintained during the most sensitive growth stages. Local soil, drainage, water control, and salinity conditions all determine whether AWD is appropriate and how the thresholds should be set.

Adopting AWD requires reliable control over when water enters and leaves the field, a way to monitor the water level, and management attention to timing. Where those conditions are met, it is one of the more widely researched water-saving practices for irrigated rice; where they are not, continuous flooding may remain more practical.