Greenhouse gas emissions and mitigation in rice agriculture

Rice paddies supply half the global population with staple food, but also account for ~48% of greenhouse gas (GHG) emissions from croplands. In this Review, we outline the characteristics of GHG emissions (CH4 and N2O) from paddy soils, focusing on climate change effects and mitigation strategies. Global mean annual area-scaled and yield-scaled GHG emissions are ~7,870 kg CO2e ha−1 and 0.9 kg CO2e kg−1, respectively, with 94% from CH4. However, emissions vary markedly, primarily reflecting the impact of management practices. In particular, organic matter additions and continuous flooding of paddies both stimulate CH4 emissions, whereas fertilizer N application rate is the most important driver of N2O emissions. Although contemporary changes in emissions are uncertain, future elevated [CO2] and warming are projected to increase CH4 emissions by 4–40% and 15–23%, respectively. Yet, integrated agronomic management strategies — including cultivar, organic matter, water, tillage and nitrogen management — offer GHG mitigation potential. In particular, new rice variety selection, non-continuous flooding and straw removal strategies reduce GHG emissions by 24%, 44% and 46% on average, respectively. However, approaches need to be optimized on the basis of seasonal CH4 emission patterns, necessitating improved quantification and reduced uncertainty in regional and global GHG estimates, especially in low latitudes.