Objectives We studied the effects of different amounts of green manure (Vicia sativa) incorporation under different N fertilization rates on wheat production and soil fertility in the system of planting Vicia sativa after wheat in Qinghai Plateau, aiming to propose an efficient combination of N fertilizer and green manure incorporation for wheat production.

Methods Filed experiments were carried out in 2023 and 2024 in Qinghai University. No N application (N0), conventional N application (N100%) and 30% nitrogen reduction (N70%) were designed as treatments. Under each N treatment, 50% (G1) and 100% (G2) of the harvested fresh green manure were returned to soil. The wheat yield and nitrogen uptake were measured. The soil chemical and microbial properties were measured for calculation of integrated fertility index (IFI). The overall benefits of different treatments were quantified using the entropy weight-TOPSIS model.

Results There were no significant differences in wheat yield, number of ears, grains per ear, thousand-grain weight, plant height, stem diameter, or ear length among the four treatments combining two nitrogen application rates and two green manure return rates (N70%G1, N70%G2, N100%G1, N100%G2). Compared to N100%, the N70% treatments significantly reduced above-ground N uptake in wheat, however, neither nitrogen harvest index nor nitrogen fertilizer use efficiency differed from N100% significantly. Between N70%G1 and N70%G2, no significant difference was detected in N harvest index and nitrogen fertilizer use efficiency, although the above-ground N uptake in N70%G1 was significantly lower than in N70%G2. In 2023, the nitrogen harvest index of N70%G1 was significantly higher than that of N70%G2. Relative to N0, the average soil bulk density in N70% treatments decreased by 5.20%, while the reduction in N100% was not significant. Soil moisture did not differ significantly among the two nitrogen application rate and two green manure return amount combining treatments. Microbial C/N ratios across treatments ranged from 10.23 to 11.09, consistently exceeding 10∶1, indicating a predominance of fungal microorganisms. Neither nitrogen application rate nor green manure return rate significantly influenced soil microbiomass carbon and microbiomass nitrogen contents. The integrated fertility index (IFI) for N70%G2 and N70%G1 treatments increased by 13.04% and 11.98%, respectively compared to N0; No significant differences were observed in total or net profits between the two nitrogen application rates and green manure return quantities. According to Entropy-weighted TOPSIS comprehensive evaluation, treatment N70%G1 achieved the highest composite score of 0.71, significantly outperforming other treatments.

Conclusions Under conditions of post-wheat green manure cultivation, incorporating half of the green manure into soil alongside with 30% of reduction of the conventional nitrogen fertilizer dosage yields the highest overall score, because the practice dose not alter wheat yield, thousand-grain weight, plant height, spike length, soil fertility and net profit significantly, compared to whole green manure incorporation combined with full nitrogen fertilizer. Therefore incorporating half of the green manure into the soil while reducing nitrogen application by 30% represents an optimal model for simultaneously achieving stable wheat yields and soil fertility enhancement and balancing ecological and economic benefits in eastern Qinghai’s agricultural region.