Importance of water regime during the non-rice growing period in winter in regional variation of CH4 emissions from rice fields during following rice growing period in China

Rice fields are either continuously flooded or drained in China in the winter (non-rice growth season). Due to great spatial variation of precipitation and temperature, there is a spatial variation of soil moisture in the fields under drained conditions during the winter season. The effect of water regime in winter on CH4 emissions during the following rice growing period and their regional variation were investigated. Soil moisture in the winter was simulated by DNDC model with daily precipitation and temperature as model inputs. Under the same management during the rice growing period, CH4 emissions was higher from rice fields flooded, compared to those from fields drained during winter. CH4 emission from rice fields correlated significantly with simulated soil moisture and with mean precipitation of the preceding winter season. Spatial variation of precipitation in winter and corresponding variations of soil moisture regimes control the regional and annual variation of CH4 emissions from rice fields in China. Keeping soils drained as much as possible during winter seems to be a feasible option to reduce CH4 emissions during the following rice growing seasons.