Effects of mild alternate wetting and drying irrigation and rice straw application on N₂O emissions in rice cultivation

Abstract. The shortage of water resources and the decline in soil organic matter (SOM) are important limiting factors affecting the improvement of rice productivity, while alternate wetting and drying (AWD) irrigation and rice straw return are considered favorable mitigation measures. However, its impact on rice yield and greenhouse gas (GHG) emissions, especially nitrous oxide (N₂O) emissions, needs to be further clarified, which is essential for the development of agronomic measures for water savings, soil fertilization and GHG reduction. Therefore, we explored the effects of mild AWD irrigation combined with rice straw return on N₂O emissions and rice yield through rice pot experiments. This study showed that N₂O emissions were mainly affected by urea application and irrigation methods, and urea application was the main reason. Compared with continuous flooding (CF) irrigation, mild AWD irrigation increased cumulative N₂O emissions, with an average increase of 28.8 %. In addition, adding rice straw to mild AWD irrigation further stimulated N₂O emissions. Compared with CF irrigation, mild AWD irrigation increased the yield-scaled N₂O emissions, and the addition of rice straw further promoted the yield-scaled N₂O emissions under mild AWD irrigation but reduced the global warming potential (GWP) by 62.9 %. Under the condition of urea application, compared with CF irrigation, mild AWD irrigation reduced nitrogen uptake by rice in the soil and rice aboveground biomass without reducing rice yield. Therefore, mild AWD irrigation combined with rice straw return is a promising agronomic measure to ensure rice yield, reduce the greenhouse effect and maintain or improve soil fertility.