Spatiotemporal characteristics and reduction approaches of methane emissions from rice fields in China

Rice is the main staple crop in China and methane (CH₄) is the second most important greenhouse gas worldwide. Therefore, it is important to reduce CH₄ emissions from paddy fields. Based on national statistical data and literature collection, we calculated and analyzed the spatial and temporal characteristics of CH₄ emissions at the rice sown-area scale and yield scale in China from 2001 to 2018 and further summarized the key processes and main influencing factors of CH₄ emissions. The results of this study showed that the total sown area of rice and area-scaled CH₄ emissions from rice fields in China showed an overall trend of first decreasing, then increasing, then decreasing again from 2001 to 2018; however, yield-scaled CH₄ emissions in all regions showed a decreasing trend. CH₄ emissions from rice fields mainly included three processes of production, oxidation, and transport, which were mainly influenced by rice varieties, soil characteristics, climatic conditions, and agronomic measures. Owing to the influence of rice sown areas, area-scaled CH₄ emissions from paddy fields in China were high in the southeast and low in the northwest, and yield-scaled CH₄ emissions were high in the south and low in the north. Based on the above findings, this study suggested reducing CH₄ emissions by applying a new rice cultivar, cropping mode, and products with high yield and low CH₄ emissions. Given the regional characteristics of CH₄ emissions in China, this study first proposed the selection of rice cultivars with high yield and low CH₄ emissions and the application of aerobic dry tillage and water-control irrigation in the southern plain region, biochar and lime in the southern hilly region, and aerobic dry tillage and partially alternative urea with ammonium sulfate in the northern rice cropping region. Finally, some suggestions were put forward related to science, technology and policy innovations for CH₄ emission reduction to provide important references for achieving the win-win target of high yield and low CH₄ emissions.