Paddy ponding water management to reduce methane emission based on observations of methane fluxes and soil redox potential in the Red River Delta, Vietnam^*

Abstract Reducing methane (CH 4 ) emissions from paddy fields that contribute to the greenhouse effect has been addressed recently through the application of the alternate wetting and drying irrigation method. However, in poorly drained areas, such as the Red River Delta in Vietnam, the soil cannot be dried immediately, and so CH 4 can continue to be produced unintentionally. Therefore, the purpose of this case study was to identify the optimal ponding water management schedule to reduce CH 4 emissions by using the measured data of ponding depth, soil redox potential (Eh), and CH 4 fluxes from field experiments and to show its effects on CH 4 emission and water conservation. Observations in the winter–spring cropping season showed that the non‐flooding period of 3–8 days suppressed CH 4 emission, and the continuous flooding period of 14–22 days caused CH 4 re‐emission. Information regarding the non‐flooding period to be maintained and the flooding period to be avoided to suppress CH 4 emission was not obtained for the summer–autumn cropping season due to abundant rainfall. The proposed schedule could suppress CH 4 emission by 27%–85% and increase the amount of conserved water by up to 18% compared with traditional flooding protocols, but it may increase irrigation water due to the frequency and the amount of re‐flooding.