Effect of organizational paddy water management by a water user group on methane and nitrous oxide emissions and rice yield in the Red River Delta, Vietnam

To mitigate the emissions of greenhouse gases from paddy fields and solve water shortage problems, sustainable and eco-friendly water management systems for rice cultivation urgently need to be constructed. Alternate wetting and drying (AWD) water management is effective and saves water. However, practical examples of AWD at the district or on-farm level are limited. We aimed to investigate the feasibility of AWD in experimental block units (conventional, weak-dry, and strong-dry) in paddy fields of about 44 ha in the Red River Delta area of Vietnam by examining the effects of intermittent irrigation (i.e., AWD) on the ponding depth, CH4 and N2O emissions, and rice yield in blocked experimental plots. Intermittent irrigation was expected to be achieved through the operation of irrigation pumps and sluice gates of water division works by the water management organization (water user group) of the district. However, the ponding depth was not controlled as initially planned because of frequent rainfall and low rate of decrease of the ponding depth in the study area. It was, however, confirmed that the period during which the ponding depth decreased below the soil surface was mostly (but not always) longer in the dry-type blocks. CH4 emissions decreased with an increase in drying period and this reduction was large in the summer-autumn season. There appeared to be no relationship between N2O emissions and water management. Rice yield decreased due to extreme drying in the summer-autumn season but was not affected by drying in the winter-spring season. This study demonstrated that CH4 emissions can be reduced and rice yield can be maintained by achieving a maximum drying index (i.e., ratio of the period during which the ponding depth is below the soil surface) of 0.6 in the summer-autumn season in the paddy fields of the target area.