Greenhouse gas emissions and water-carbon cost-adjusted yield of drought-tolerant rice under varying irrigation amounts in the Jianghan Plain of China

Water management plays a crucial role in achieving carbon mitigation, yield stability, and water conservation in rice production. To explore the effects of irrigation amount on greenhouse gas emissions, yield, and economic benefits, this study examined drought-tolerant rice paddies in the Jianghan Plain under five irrigation amounts. Over two consecutive rice-growing seasons, the dynamics of CO2, CH4, and N2O emissions, as well as soil physicochemical properties, were systematically monitored. Global warming potential (GWP) and greenhouse gas intensity (GHGI) were calculated for estimating the greenhouse effect. Yield benefits were further evaluated by incorporating water and carbon related cost corrections, thereby the optimal irrigation range was identified. The main findings are as follows: irrigation primarily influences the paddy field environment by regulating soil moisture and redox potential (Eh) conditions, thereby driving microbial processes related to greenhouse gas emissions. Higher irrigation amounts promote CH4 emissions while suppressing N2O emissions, whereas lower irrigation amounts reduce CH4 emissions but increase N2O emissions, indicating a clear trade-off between the two. Fitting results show that rice yield first increases and then decreases with increasing irrigation amount, GWP increases with increasing irrigation, and GHGI overall shows a decreasing-then-increasing trend, indicating that moderate irrigation is more conducive to achieving both high yield and emission reduction. Comprehensive analysis indicates that, under the conditions of this study, 410–650 mm is a relatively suitable irrigation range; maximizing rice yield while minimizing irrigation amounts and improving net yield benefits after accounting for water consumption and carbon emissions.