Effects of fertilizer addition on soil organic carbon content in Chinese farmland: a meta-analysis

Fertilization regimes have been widely practiced to increase soil organic carbon (SOC) in Chinese farmland, but the findings of various studies are often widely divergent. Therefore, a comprehensive review of the impacts of fertilization regimes on SOC is needed. In this study, a meta-analysis based on 57 peer-reviewed articles was conducted to examine the effects of fertilization regimes on SOC in China. On average, the inorganic fertilizer combined with organic fertilizer regime (NPKOF) represented the most effective approach, increasing SOC by 42.6%; this was followed by the organic fertilizer regime (OF, 41.6%) and the inorganic fertilizer regime (NPK, 15.8%). Further analysis suggested that the effects of fertilization regimes were more pronounced in areas with relatively lower clay content, higher aridity index, longer experimental duration or higher soil pH. We also highlight the importance of considering local environmental factors (e.g., climate and soil conditions) in identifying appropriate fertilization regimes for maintaining soil health, mitigating greenhouse gas emissions while ensuring crop productivity. In conclusion, although NPK addition can significantly enhance SOC content, the combined application of inorganic with organic fertilizer is very important in maintaining and improving the current SOC content across China, especially in arid regions (e.g., Northwest, lower MAP regions and higher aridity index).