Deep tillage enhanced soil organic carbon sequestration in China: A meta-analysis

The increasing atmospheric carbon dioxide (CO2) causes serious environmental problems, soil organic carbon (SOC) sequestration is suggested as an efficient strategy to offset global CO2 emissions. Deep tillage (DT) can change soil properties and the input and loss of OC, and then influence SOC sequestration across the whole soil profile. However, the effect of DT on SOC sequestration relative to conventional tillage (CT) under different environmental factors and management practices is unclear in China. In this study, we evaluated the response of SOC stock to DT based on collected field data (447 observations) with a meta-analysis. DT significantly increased SOC stock by 7.36% over CT, with a greater increase for subsoiling (8.76%) than for deep ploughing (DP) (5.85%). Subsoiling enhanced SOC across the 0–40 cm soil layer and the greatest increase occurred at 0–10 cm layer (11.41%); DP enhanced SOC stock at 10–40 cm layer, but had no effect on SOC of 0–10 cm layer. DP and subsoiling did not affect SOC storage below 40 cm depth. According to subgroup analysis, the high rainfall, fine soil texture, residue retained, double cropping, and high rate of N fertilization greatly promoted SOC stock compared with the low rainfall, sandy texture, residue removal, monoculture, and low N fertilizer input under DT. DT significantly enhanced SOC storage under low initial SOC (<15 g kg−1), but did not affect SOC when the initial SOC exceeded 15 g kg−1 compared with CT. However, the experiment duration, initial SOC and bulk density (BD) did not significantly affect the response of SOC to DT. Overall, this study has supplied a reference for SOC management in mitigating climate change, and the specific environmental factors and management practice should be considered when utilizing DT to enhance SOC sequestration in different regions of China.