Soil Organic Carbon Stock Dynamics Under Different Conservation Practices from 1980‐2022 in the Mollisol Region of Northeast China: A Meta‐Analysis Combined with Random Forest Model

Soil organic carbon (SOC) stocks is one of the most important indicators of soil health and C sequestration. Understanding how conservation practices affect the SOC stocks in the agricultural soils is important for soil carbon sequestration and climate change mitigation. However, limited studies have been conducted to investigate the SOC dynamics under different conservation practices and their interactions with climatic variables, as well as the relative importance of each explainable factor. In this study, we evaluated the response of SOC stocks to different conservation measures (e.g., no-tillage, reduced tillage, deep tillage, and straw return) based on collected field data (871 observations) with a meta-analysis method. Additionally, we further investigated how SOC dynamics are affected by the conservation practices with various climatic variables and soil properties (e.g., soil pH, bulk density, depth, initial SOC, and texture) and duration period. The results show that the change rate of the SOC stock in the Mollisol region of Northeast China significantly increased from 1980 to 2022, with an average annual increase rate of 0.16-14.17%. The SOC stock change was significantly affected by the conservation practices. Moreover, the changes in SOC stock due to conservation practices were found to be greatly affected by various climatic variables, soil properties, and duration period. In addition, the initial SOC stock was identified as the most important factor for SOC stock, with the relative importance values of 33.4%, 29.4%, 29.0%, and 34.1%, respectively. Our findings provide some recommendations for enhancing SOC sequestration in agricultural regions by implementing conservation practices.