Effects of soil water content and rice straw incorporation in the fallow season on CH4 emissions during fallow and the following rice-cropping seasons

Methane (CH4) emissions from paddy fields are believed to contribute to the greenhouse effect. Yet, in the literature, only a few reports are available on the effects of soil moisture regime and straw application in the non-rice-growing season separately on CH4 emissions during the rice-growing season. The objective of this study was to investigate CH4 emissions during the winter fallow and the following rice-growing season as affected by soil moisture regime and rice straw application during the fallow season. The experiment was designed to have 10 treatments, that is, five soil water contents (18%, 38%, 59%, and 79% of soil water-holding capacity [SWHC] and flooding; hereafter, W18, W38, W59, W79, and W100) and two rice straw application rates (0.91 and 4.55 g kg(-1) dry soil; hereafter, Sl and Sh) during the fallow season. Both W100 and W79 showed obvious CH4 emissions during the fallow season, contributing 5.3% and 5.9% (Sl) and 34.8% and 27.8% (Sh), respectively, to their gross CH4 emissions, which increased significantly with the rising soil water content in the fallow season, except for W18. Rice straw application significantly affected gross CH4 emissions, but its effect was strongly influenced by soil moisture. The CH4 emissions per unit weight of rice straw applied of W38 and W59 were 9% and 16%, respectively, as much as that of W100. The findings demonstrate that keeping the soil water content in the range of 38-59% SWHC in the fallow season is important for a reduction in CH4 emissions.