Co-application of leguminous and non-leguminous green manures enhances subsequent wheat yield stability in saline-alkali soils

The incorporation of green manure into cropping systems is recognized as an effective practice for improving environmental sustainability, particularly in irrigated agroecosystems such as the Hetao Irrigation District. However, the effect of green manure as a preceding crop in regulating subsequent wheat productivity and soil functioning in saline soils under limited nitrogen (N) inputs remains insufficiently understood. To address this gap, a 9-year field experiment was conducted to evaluate the effects of green manure types (non-leguminous feed rape (GMR), leguminous hairy vetch (GMV), and their combined application (GMRV) and N application rates (N150, 150 kg N per ha; N0, no N input) on multi-year spring wheat yield, soil ecosystem multifunctionality (EMF), and microbial resource limitation. The results showed that only green manure types had significant influence on subsequent yield and stability except for year. Compared with GMR, the GMRV treatment increased average yield by 17.2% under N150 and enhanced yield stability by 21.7% and 22.2% under N150 and N0, respectively. In addition, GMRV markedly enhanced soil organic carbon (SOC), enzyme activities, and EMF across both the wheat-growing and green manure seasons. Positive relationships were observed among SOC, total nitrogen (TN), EMF, and crop yield. Microbial communities were primarily constrained by C and N availability. GMRV reduced the microbial C limitation during the green manure season, while GMV alleviated the microbial C limitation at spring wheat season. In conclusion, the combined application of leguminous and non-leguminous green manure improved crop productivity and soil functioning by promoting SOC accumulation, nutrient availability, and ecosystem multifunctionality, while alleviating microbial resource constraints. This approach offers a promising pathway for reducing nitrogen fertilizer dependence in saline agroecosystems such as the Hetao Irrigation District.