The Effects of Different Tillage and Straw Return Practices on Soil Organic Carbon Dynamics from 1980 to 2022 in the Mollisol Region of Northeast China

Understanding how conservation practices involving tillage and straw return practices affect the soil organic carbon (SOC) in farmland is important for soil carbon sequestration and climate change mitigation. However, limited studies have been conducted to investigate and compare the magnitude and variability of the main conservation practices concentrated in grain-producing regions. In this study, we evaluated the SOC response to the main practices (e.g., no tillage, reduced tillage, deep tillage, and straw return) in the Mollisol region of Northeast China based on collected field data (871 observations) using a combination of meta-analysis and random forest (RF) methods. The results show that the SOC change rate significantly increased from 1980 to 2022, with an average annual increase rate of 0.19–14.92%. Straw return had maximum effects on SOC of 17.44% when the soil pH > 7.5 and 15.22% when the initial SOC < 10 g kg−1. The RF results indicate that the initial SOC is the most important factor for SOC, with relative importance values of 33.4%, 29.4%, 29.0%, and 34.1% for SOC under the four practices, respectively. These findings are essential for the implementation of conservation practices to improve carbon sequestration and grain production in eco-agricultural regions.