Spatiotemporal Effects of Soil and Water Conservation Measures on Soil Organic Carbon Enhancement in China: A Meta-Analysis

Soil erosion exacerbates soil organic carbon (SOC) loss, whereas soil and water conservation measures (SWCMs) mitigate SOC loss and promote SOC accumulation. Despite current research on the influence of SWCMs on SOC in different areas, a national synthesis of these studies to comprehensively understand the mechanism of change in SOC is still lacking. Therefore, We conducted a meta-analysis of 1015 SOC observations to clarify the spatiotemporal effects of SWCMs on SOC. The results revealed that in most regions in China, straw mulching and terraceing greatly enhanced SOC by 10.74%–22.63% and 17.94%–27.0%, respectively, compared with the initial baseline levels. Afforestation also showed exceptional efficacy with SOC increased by 109.80% in Southern Red Soil Region, significantly larger than other areas (34.58%–76.47%). This exceptional increase is attributed to a low initial SOC baseline and rapid biomass accumulation following afforestation. All tillage measures (straw mulching, straw returning, no-tillage, and contour tillage) induced maximal SOC gains (6.82%–75.77%) within 5–10 years from the baseline. For afforestation and grass planting, longer durations of 21–30 and 11–20 years were required for the best promotion effect, with SOC increased by 82.94%–110.01% and 11.29%–77.71%, respectively, over the initial values. Similarly, engineering measures like terracing (14.11%–60.96%) and fish-scale pits had optimal enhancement effects (79.86% on the Loess Plateau) on SOC storage in years 11–30 relative to the initial conditions. Further boosted regression tree analysis revealed that soil total nitrogen was the primary driver of SOC increases across all measures. These findings are essential for the implementation of ecological restoration projects to mitigate CO₂ in China.