Higher rice grain yield and lower methane emission achieved by alternate wetting and drying in central Vietnam

Rice is the main staple food for more than half of the world's population, but rice cultivation is a significant source of atmospheric methane (CH4). Alternate wetting and drying (AWD) reduces CH4 emission from paddy field, but the effect on rice yield remains unclear. Organic soil amendment increases grain yield but simultaneously increases CH4 emission. Therefore, the combination of AWD and organic amendment may compensate for each other's shortcomings. The objective of this study was to assess whether AWD and organic amendment can increase rice yield while mitigating CH4 emission. The experiments were conducted in a farmer's paddy field in Thua Thien Hue province, Vietnam, during five consecutive rice growing seasons in 2019-2021. Two water management practices, continuous flooding (CF) and AWD, with (+O) or without (-O) the application of a commercially available organic fertilizer were examined under normal cultivation conditions. Compared with CF, AWD significantly reduced CH4 emission by 34 %, increased nitrous oxide (N2O) by 46 %, and increased grain yield by 4.4 %. The +O treatment significantly increased the yield by 3.7 % relative to-O. Relative to CF-O by season, AWD+O significantly increased the yield. The integrated global warming potential of CH4 and N2O emissions was decreased by 33 % and irrigation water use was reduced by 33 % in AWD plots relative to that in CF plots. These results indicate that AWD by itself has the potential to increase rice yield as well as reduce CH4 emission, and the combination of AWD with organic amendment would ensure yield increase.