Effects of Irrigation Regime and Rice Variety on Greenhouse Gas Emissions and Grain Yields from Paddy Fields in Central China

Increasing irrigation water scarcity is threatening global rice production and sustainability. Accordingly, the cultivation of drought-resistant rice varieties has been strongly advocated to reduce the consumption of irrigation water. However, it remains unclear how the cultivation of drought-resistant rice affects greenhouse gas emissions. Here, a two-year field experiment was conducted to elucidate the effects of irrigation regimes (AWD, alternate wetting and drying; CF, continuous flooding) and rice varieties (drought-resistant rice 7Y88 and 7Y370, and conventional rice HHZ) on the grain yields and greenhouse gas (methane [CH4] and nitrous oxide [N2O]) emissions from paddy fields. The experiment was performed in a split-plot design with three replications. The results showed that AWD significantly reduced water inputs and grain yields compared with CF in both rice growing seasons. On average, 7Y88 and 7Y370 significantly enhanced the water use efficiency by 37.6% and 51.5%, and the grain yields by 33.9% and 47.0% relative to HHZ, respectively. A trade-off between CH4 and N2O emissions was observed under irrigation regimes. Compared with CF, AWD significantly reduced cumulative CH4 emissions by 64.9%, while increased cumulative N2O emissions by 160.0%, and decreased the grain yield by 11.6% on average. AWD also significantly reduced the global warming potential (GWP) and greenhouse gas intensity (GHGI) by 42.2% and 31.6%, respectively. Significant differences (p < 0.05) in GHG emissions, GWP and GHGI were observed between drought-resistant rice varieties and HHZ. The rice variety 7Y370 resulted in the lowest CH4 and N2O emissions, GWP and GHGI among all varieties under both irrigation regimes. These results indicate that the rice variety 7Y370 can be recommended to simultaneously mitigate GWP and maintain grain yields.