Yield and nitrogen use efficiency in optimized oat-common vetch mixtures on the Qinghai–Tibet plateau

This study investigated the systemic effects of various nitrogen (N) regimes and phosphorus (P) additions on growth traits, N accumulation, and N fixation efficiency in mixed sowing systems of oat ( Avena sativa L.) and common vetch ( Vicia sativa L.) on the Qinghai-Tibet Plateau. Using a combination of field and pot experiments with a series of N-P co-application treatments, this study systematically measured the biomass, N accumulation, N fixation efficiency, and land equivalent ratio (LER) of two crop species in a mixed sowing system, and compared the results with monoculture treatments. Results indicated that N-enriched conditions significantly enhance biomass, and N accumulation in both species, with the A1V1 treatment (1:1 ratio) showing the highest aboveground biomass (1164 g·m -2 ) and an optimal Land Equivalent Ratio (LER) of 1.86. Phosphorus application improved N fixation and transfer, while moderate N-P co-application optimized N utilization within the system. Mixed sowing demonstrated superior N fertilizer utilization compared to monoculture, promoting sustainable agriculture by enhancing crop resilience and productivity. Adjustments in N-P addition based on specific soil conditions are essential to maximize benefits and avoid negative impacts on biological N fixation.