Soil carbon sequestration and aggregate stability improvement by tillage methods in China's Loess Plateau

Long-term mono-conservation tillage may not meet the needs to improve soil organic carbon (SOC) sequestration and soil structure stability. A 12-year field experiment was conducted in Northwest China to explore the mechanisms of tillage for improving SOC sequestration, humic substances and soil structure. Rotational tillage, no-tillage and subsoiling increased wheat yield, maize yield and crop residue C by 3%-15%, 8%-15% and 4%-15%, respectively. Meanwhile, rotational tillage, no-tillage and subsoiling increased the conversion rate of crop residue C, resulting in 25%-73% higher SOC sequestration than plowing. Fulvic acid, humic acid and SOC were increased by no-tillage at 0-0.1 m depth, by subsoiling at 0-0.1 m and 0.2-0.4 m depths and by rotational tillage at 0-0.4 m depths. Humic acid and fulvic acid improved soil aggregation. No-tillage increased mean weight diameter (MWD) at 0-0.1 m depth. Rotational tillage and subsoiling improved aggregate stability at 0-0.4 m depths. Due to higher aggregate stability, rotational tillage, no-tillage and subsoiling increased SOC concentrations within macroaggregate and microaggregate, contributing to SOC sequestration. No-tillage rotated with subsoiling had the highest crop yield, SOC stock and MWD, which was the optimal practice in Northwest China.