Green Manure Species Regulate Carbon Inputs and Soil Organic Carbon Sequestration in a Dryland Winter Wheat System on the Loess Plateau of China

ABSTRACT

Green manure (GM) crops are increasingly promoted as a strategy to enhance soil organic carbon (SOC) sequestration and sustain crop productivity in dryland agroecosystems. However, species‐specific effects of GM on long‐term SOC dynamics and stabilization remain poorly quantified in semiarid cropping systems. A five‐year field experiment was conducted on the Loess Plateau of China to evaluate the effects of two GM species, black bean ( Phaseolus vulgaris L.) and rapeseed ( Brassica napus L.), integrated into a winter wheat rotation. Treatments included black bean‐winter wheat (BW), rapeseed‐winter wheat (RW) and fallow‐winter wheat (FW), with FW serving as the control. Results showed that both GM species significantly increased SOC stocks relative to fallow, with increases of 9.5% for BW and 8.7% for RW after 5 years. To elucidate the mechanisms underlying SOC accumulation, a nylon‐bag decomposition experiment was conducted to quantify biomass decomposition and carbon (C) release patterns. Black bean residues decomposed rapidly during the early stages, whereas rapeseed residues exhibited greater cumulative decomposition over time, indicating contrasting residue turnover dynamics between species. Model simulations of SOC dynamics estimated an annual SOC decomposition rate of approximately 2% and a crop‐derived C retention coefficient of 39%. Long‐term projections suggested that SOC stocks would stabilize at higher equilibrium levels under BW (47.75 Mg C ha ⁻¹ ) compared with RW (38.52 Mg C ha ⁻¹ ). Overall, GM species differed markedly in their contributions to SOC sequestration and residue turnover in semiarid conditions. Black beans promote greater long‐term SOC stabilization, whereas rapeseed residues decompose more rapidly. These results highlight the importance of GM species selection for SOC sequestration and soil fertility management in dryland agroecosystems. Our findings demonstrate that GM species vary substantially in their capacity to convert residue‐derived C into stable SOC pools, indicating that residue quality and decomposition dynamics are key determinants of long‐term C stock in dryland agricultural systems.