Water-saving irrigation and delayed sowing increased the emission intensity of CH4 and N2O in the rice-wheat rotated field under nighttime warming

Climate change and water shortage are the two important driving factors for food insecurity. It is a common concern to ensure food security to cope with climate change by adopting the best management practices (e.g., irrigation methods and sowing date). A field simulation experiment was conducted to investigate the effects of management practices (water-saving irrigation and delayed sowing) on yield and greenhouse gas emissions (CH4 and N2O) in a rice-wheat rotated field under nighttime warming. A randomized complete block design with three factors and two levels was adopted in this study. The two levels of nighttime temperature were set as ambient temperature (CK, control) and nighttime warming (NW). The crop canopy was covered with aluminum foil film at night (19:00-6:00) to simulate nighttime warming. The two levels of irrigation in rice-growing season were set as conventional irrigation (F, intermittent flooding with 5-cm water layer) and water-saving irrigation (M, moistening without water layer). The two levels of sowing date of winter wheat were set as normal sowing date (NS) and delayed sowing date (DS). The results indicated that, compared with the control, nighttime warming or water-saving irrigation decreased rice biomass and yield by 14.69%-18.16% and 7.27%-9.14%, respectively, whereas delayed sowing increased wheat yield by 0.71%. Compared with the CH4 efflux with ambient temperature and flooding irrigation, CH4 efflux from rice field significantly declined with nighttime warming or water-saving irrigation but significantly increased with nighttime warming under water-saving irrigation. Under ambient temperature, compared with flooding irrigation, water-saving irrigation significantly reduced the cumulative CH4 emission by 79.46% but significantly promoted the cumulative N2O emission by 97.21%. Under nighttime warming, water-saving irrigation significantly increased the cumulative CH4 and N2O emissions by 39.98% and 45.62%, respectively, compared with flooding irrigation. Compared with the control, delayed sowing significantly reduced the cumulative N2O emission by 21.46%-53.77% in wheat field. The contribution of CH4 emissions from the rice field was dominant in all the treatments. Nighttime warming significantly decreased the greenhouse gas emission intensity (GHGI) in the rice-wheat rotated field with flooding irrigation and normal sowing but significantly increased GHGI in the field with water-saving irrigation and delayed sowing. Given the increased yield and environmental benefits, this study suggests that conventional irrigation (intermittent flooding) for rice and normal sowing for wheat are the effective practices for the rice-wheat rotated field to cope with global warming in the lower reaches of the Yangtze River.