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.
AWD works well in lowland rice-growing regions where soils may be drained every week.
High rainfall could obstruct AWD. The field won’t be able to dry during the rice-growing season if rainfall is more than the amount of water lost to evapotranspiration and seepage.
Farmers need to be in charge of their crops’ irrigation and have the assurance that they will have access to water once the fields have drained. Because there is no guarantee of water supply when fields need to be re-flooded, AWD is not advised for rainfed rice.
After rice fields are flooded, the anaerobic breakdown of organic matter results in the production of methane in wet or “paddy” rice soil. The creation of methane (CH4), which occurs under anaerobic conditions, is stopped by allowing the field to drain, so limiting the overall amount of CH4 emitted throughout the growing season.
Impact on Production
AWD not only saves water but also increases grain yield. Sufficient oxygen is supplied to the rice system which increases soil organic matter and hence the soil fertility which helps to realize enhanced yields.
Impact on Water Usage
In Alternate wetting and drying, since no continuous standing water is maintained during crop growth, the number of irrigation events is reduced. There is a net saving of water by 35%. AWD can save up to 660 liters of water per kg of paddy. The farmers are benefitted in water-scarce situations and the reduction in water for irrigation helps to utilize fresh water for other uses. Reduced withdrawal of groundwater also saves diesel consumption for water pumps.
Impact on Soil
The drying phase helps root growth and its sustainability for water transport to rice plants even under low soil moisture conditions. Also, the drying and wetting of soils alternately release phosphorus by physical and biological processes. AWD reduces the occurrence of lodging and helps plants grow better tillers, thereby increasing soil stability. This also reduces harvesting costs with the adoption of mechanical harvesting techniques.
Impact on Climate
Rice cultivation is a major source of methane emissions. AWD reduces the global warming potential of methane and nitrous oxide emissions by 45-90% compared to continuously flooded cultivation. The standing water blocks oxygen from penetrating the soil and promotes the growth of methane-producing bacteria. Shorter flooding intervals reduce methane emissions by 95%.
Impact on Plant Protection
Alternate wetting and drying also reduces the infestation of pests and diseases compared to the traditional methods of cultivation. AWD enhances root depth and density making paddy more drought and disease-resistant. With improved soil aeration and increased water and nutrient intake, crop growth is regulated.
Impact on Farmers
Alternate wetting and drying irrigation practices increase the net profit of farmers by lowering water costs, and pumping costs. It enables better tilling with enhanced crop yields. Farmers can balance irrigation by knowing the water level status and also achieve reduced methane emissions.