Abstract: Rice production consumes large amount of water resource and is an important greenhouse gas (GHG) source. Water management in paddy fields is the key factor controlling GHGemission. As an important agricultural practice for water saving and GHG emissions reduction, alternate wetting and drying (AWD) irrigation has been commonly applied in many Asian countries, such as China, Philippines, Vietnam, and India. We analyzed the effects of AWD irrigation on GHG emissions mitigation and other ecological efficiency, including water saving potential and rice yields. AWD significantly decreased methane (CH₄) emission and increased nitrous oxide (N₂O) emission. The global warming potential (GWP) mitigation was dependent on the increases of N₂O emission. Coupling with fertilizer management, such as optimizing the fertilizer type and application method, AWD is conducive to the CH₄ and N₂O mitigation. Rice yield was affected by the water stress threshold of AWD. Mild water stress (field was re-flooded when soil water potential dropped to -15±5 kPa) could reduce irrigation water inputs and maintain rice yield, while severe water stress (field was re-flooded when soil water potential dropped to -30±5 kPa) significantly reduced yield. AWD improved soil aeration and microbial activities, with positive impacts on decomposition of soil organic matter. Encouraging farmers to develop watersaving and efficient agriculture scientifically would be beneficial to cost reduction and income increase.

Key words: water management, alternate wetting and drying irrigation, rice production, greenhouse gas emissions mitigation, water stress threshold.