Paddy–Upland Rotation Improves Rice Growth and Reduces Greenhouse Gas Emissions in Winter Paddy Fields

From May 2019 to May 2022, a field experiment was conducted to clarify the effects of paddy–upland rotations on rice yield and greenhouse gas emissions in winter paddy fields. Four types of rotation pattern, rice–oilseed rape, rice–radish, rice–faba bean, and rice–fallow (flooded), were investigated and the N2O, CH4, and CO2 emissions in situ and rice yield were determined. The results showed that the paddy–upland rotation mode required fertilization during the winter cropping season. Compared with the rice–fallow (flooded) mode, the flux rate and annual cumulative emissions of N2O were significantly higher in the paddy–upland rotation modes. The rice–radish mode had the highest flux rate and annual cumulative emissions of N2O. When the soil in each paddy–upland rotation mode was exposed to air in winter, the soil redox potential increased and reducing substances were oxidized. Compared with the rice–fallow (flooded) mode, the flux rate and annual cumulative emissions of CH4 significantly decreased in the paddy–upland rotation modes, with the rice–radish mode producing the lowest flux rate and annual cumulative emissions of CH4. Fertilization and crop planting were conducted in winter, and the soil moisture was low. Compared with the rice–fallow (flooded) mode, the flux rate of CO2 of the paddy–upland rotation modes increased significantly. The flux rate of CO2 in the rice–oilseed rape mode was the highest. Furthermore, the N2O and CH4 emissions produced during the rice season and annually were significantly positively correlated with those in the winter season, indicating that the winter season had a significant effect on greenhouse gas emissions from winter paddy fields. Because of the significantly higher annual cumulative emissions of CH4 and the significantly lower rice yield in the rice–fallow (flooded) mode than in the paddy–upland rotation modes, this mode’s global warming potential (GWP) and greenhouse gas intensity (GHGI) during the rice season are significantly higher than those of the paddy–upland rotation modes.