Optimizing organic fertilizer substitution for yield-carbon tradeoffs in staple crops across China

Agricultural soil plays a dual role in the terrestrial carbon cycle, acting both as an important carbon reservoir and a major source of greenhouse gas (GHG) emissions. Organic fertilizer substitution (OFS) is thought to be an effective management strategy to improve soil carbon(C) content and soil health, while at the same time maintaining crop productivity. However, the optimal ratio of OFS that can simultaneously enhance crop yield and reduce soil C losses remains unclear for sustainable agricultural soil management. Therefore, in this study we access the optimized ratio of OFS across China and quantify the responses of crop yield and net C balance to variations in OFS. We compiled a database of crop yield and net C balance—defined as changes in soil organic carbon (SOC) and greenhouse gas (GHG) emissions—for wheat, maize, and rice production in China. This database was used to develop a machine learning model to predict crop yield, GHG emissions, and net C balance for the three crops, which was subsequently upscaled using gridded environmental datasets representing the major crop production systems across China. The results showed that the optimal OFS ratio varied between 10% and 90%, with most values concentrated in the range of 20–40%. Under the optimal OFS ratio, crop yields increased at the national scale, with greater yield gains observed for maize and rice than for wheat. In addition, optimal OFS significantly enhanced the net C balance of the three major cropping systems across China, generating additional carbon sinks of 1081.81, 930.05, and 510.76 Tg CO₂-eq for maize, rice, and wheat, respectively, compared with business-as-usual (BAU) scenarios. Overall, our results indicate that OFS represents an optimal field management strategy that not only enhances agronomic productivity but also improves environmental performance.