Green manure rotation and application increase rice yield and soil carbon in the Yangtze River valley of China

The addition of organic matter via green manure rotation with rice is considered a smart agricultural practice to maintain soil productivity and support environmental sustainability. However, few studies have quantitatively assessed the impact of green manure rotation and application on the interactions between agronomic management practice, soil fertility, and crop production. In this study, 800 pairs of data from 108 studies conducted in the agricultural region of the Yangtze River, China were assessed, and random forest (RF) modeling was performed to evaluate the effect of green manure rotation and application on rice yield and soil properties. Compared to a winter fallow system, rotation and application of green manure significantly increased rice yield and soil organic carbon (SOC) by 8.1% and 8.4%, respectively. According to the RF models, rice type, green manure application rate and duration, mineral and organic nitrogen application rates, and initial SOC content and soil pH were identified as the main drivers for rice yield and SOC changes. Marginal benefit analysis revealed that green manure application rates for early rice in double cropping system and the rice in single cropping system were approximately 20 and 261 ha–1 (fresh weight), respectively. Further, the optimum green manure application rate was approximately 25 t ha–1 (fresh weight) for carbon sequestration. However, it should be noted that green manure application to soils with high SOC level might result in the soils becoming a net carbon source. Our study contributed scientific and quantitative indicators for achieving the greatest benefits in rice yield and increasing SOC upon application of green manure.