The effective water management practice for mitigating greenhouse gas emissions and maintaining rice yield in central Japan

Water management practices such as flooding, intermittent drainage (ID), and midseason drainage are important factors for greenhouse gas emissions from paddy fields and rice yields. We measured the direct emissions of methane (CH4) and nitrous oxide (N2O) simultaneously with indirect emissions of carbon dioxide (CO2), CH4, and N2O from drainage pipes in central Japan. These emissions were measured under three types of water management practices: ID, continuous flooding (CF) except midseason drainage, and a compound (CP) treatment with a combination of flooding, midseason drainage, and ID. Cumulative total direct emission of CH4 and N2O in terms of CO2 equivalents was lowest in CP, being 47.1% lower than the highest emission in CF. Cumulative total indirect CO2 equivalent emission of CH4 and N2O was also lowest in CP. More than 90% of gas emissions were direct emission in all treatments. Rice yield was highest for CP, with yields in CF and ID being 7.8% and 43.8% lower, respectively. However, there was little difference in rice quality between treatments. Early drainage in the ID treatment appeared to contribute to lower yield components of numbers of panicles and spikelets per panicle. It also may have promoted nitrification and denitrification, and thus caused the increased direct and indirect N2O emissions. The enhanced nitrification and denitrification may have contributed to significant nitrogen losses in the early vegetative growth stages that would negatively affect the determination of the panicle and spikelet yield components. Therefore, the CP treatment may be an effective water management practice for mitigating greenhouse gas emission and maintaining rice yield in central Japan.