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

Abstract

The addition of organic matter via green manure rotations in paddy rice has previously been proposed as a smart agricultural practice to maintain soil productivity and support environmental sustainability. However, to date, only a few studies have assessed quantitatively the impact of green manure application on the interactions between agronomic management practices, soil fertility, and crop production. In this study, 800 pairs of data from 108 studies, conducted in the Yangtze River agricultural region of China were assessed, and a meta-analysis was carried out to evaluate and quantify the effect of green manure application on rice yield and soil properties. Firstly, compared to a winter fallow system, amendment with green manure significantly increased paddy rice yield and soil organic carbon (SOC) by 8.1% and 8.4%, respectively. Secondly, analysis using a Random Forest model revealed that paddy rice type, green manure application rate and duration, mineral and organic N fertilizer rate, and initial SOC and pH were identified as the main drivers for paddy rice yield and SOC change. Finally, Marginal Benefit Analysis (MBA) revealed that green manure application rates for production in early rice of double cropping rice (ER) and single rice (SR) were approximately of 20 and 26 t ha-1 respectively. and further, for carbon sequestration, that the optimal rate was ~25 t ha-1. It should, however, be noted that green manure application to soils with already high SOC level might result in the soil becoming a net C source. The study supported the scientific and quantitative indicators for achieving the best benefits of paddy rice yield and SOC increase after green manure application.