Annual greenhouse gas emissions from a rice paddy with different water-nitrogen management strategies in Central China

Current water-nitrogen (N) management strategies are necessary to be improved to increase crop productivity while reducing environmental costs. However, the effects of improved water-N management strategies on paddy CH4 and N2O emissions simultaneously generated during the growing and non-growing seasons have not been explored. Therefore, in this study, four water-N management practices—urea plus conventional irrigation (UREA+CI), urea plus alternate wetting-drying irrigation (UREA+AWD), controlled-release N fertilizer plus CI (CRNF+CI), and CRNF plus AWD (CRNF+AWD)—were evaluated in a 3-year field experiment following a randomized complete block design with three replications each. The results demonstrated that during rice growing seasons, CH4 emissions significantly decreased by 12.6–44.9% under UREA+AWD and by 17.2–32.1% under CRNF+CI, compared to UREA+CI, respectively, and CRNF+SWD showed the highest mitigation potential. N2O emissions were reduced in CRNF treatments (CRNF+CI and CRNF+AWD) but increased by replacing CI with AWD during rice growing seasons, suggesting the potential effects of water regimes on N2O emissions. Furthermore, AWD and CRNF reduced CH4 emissions during the land preparation period before the late rice growing season and the fallow period, whereas CRNF treatments triggered the release of N2O in the fallow period. Moreover, there were no significant differences in soil organic carbon sequestration rates among the treatments. The results indicated that AWD, CRNF and their combination significantly reduced annual net total greenhouse gas emissions without yield loss. Collectively, this study unravels the potential of alternative water-N management strategies to improve rice yields while minimizing GHG emissions in double rice cropping systems.