Abstract:

Balancing soil carbon sequestration with crop productivity is a pivotal challenge in sustainable agriculture.Leguminous green manure incorporation offers a potential pathway, yet the mechanisms underlying its synergywith reduced nitrogen fertilization in achieving co-benefits for soil carbon sequestration (SCS) and yield stabilityrequire further elucidation. A field experiment was conducted from 2023 to 2025 in an oasis irrigated area ofNorthwest China to evaluate five nitrogen application rates (100 % (N100, traditional nitrogen application),90 % (N90), 80 % (N80), 70 % (N70), and 60 % (N60)) under leguminous green manure incorporation on maizeyield, soil organic carbon storage (SOCs), and the underlying mechanisms. The results indicated that the N80treatment effectively maintained maize grain yield while significantly enhancing soil organic carbon storage.This synergistic effect was attributed to the improvement of soil aggregate stability and the enhancement of soilorganic carbon chemical stability, which was specifically manifested in the N80 treatment exhibiting the highestaromaticity index and the lowest proportion of labile functional groups. Specifically, the N80 treatmentincreased the proportion of macro-aggregates (>2 mm) and mean weight diameter (MWD), geometric meandiameter (GMD), and the proportion of aggregates > 0.25 mm (DRo.25). Concurrently, scanning electron mi-croscopy observations indicated that the N80 treatment promoted the formation of abundant honeycomb-likepores and ridge-shaped surface structures in the soil. These unique microstructures effectively enhanced theaccumulation of organic carbon within aggregates. Fourier transform infrared spectroscopy (FTIR) revealed thatthe N80 treatment enhanced the aromaticity index (Aromatic C/Aliphatic C) of SOC and reduced the proportionof labile functional groups (specifically, O-H/N-H and C-O groups indicative of polysaccharides and amides).Structural equation modeling confirmed that green manure incorporation with 20 % nitrogen reduction primarily facilitated SOC sequestration by improving aggregate stability and optimizing organic carbon composi-tion. Regression analysis based on a multi-objective comprehensive evaluation model revealed that a nitrogenreduction of 18.74 % is optimal for systems with green manure incorporation. In conclusion, reducing nitrogenapplication by 20 % combined with leguminous green manure incorporation is an optimal management strategyfor synergistically enhancing SOC sequestration, improving soil structure, and securing crop yield in oasisagroecosystems.