Mixed cropping green manure can simultaneously improve the nutrient yield and quality of spring wheat grain under reduced chemical nitrogen supply

Mix-cropping green manure and reduced N improved nutrition production of wheat grain. Mix-cropping green manure (HCV) and reduced N increased nutrition and processing quality. HCV with reduced N by 20% enhanced N accumulation, remobilization, and assimilation. Ensuring the provision of adequate and nutritious food for humans through sustainable agricultural development poses a major challenge. Optimized nitrogen supply is one of the key factors to improve crop grain yield and quality. Green manure is often used to optimize nitrogen supply in crop production, but it is unclear whether green manure maintains grain yield and quality of spring wheat while reducing chemical nitrogen input. A split-plot field experiment of various varieties of green manure and mixed cropping green manure was established in an arid area since 2018. This study aimed to explore the feasibility of mixed common vetch and hairy vetch, which could simultaneously maintain high nutrition production and grain quality of spring wheat to reduce chemical nitrogen input and reveal the mechanism of nitrogen metabolism. We discussed the effects of green manure and reduced chemical nitrogen on nutrition yields, amino acid contents, vitamin B contents, mineral contents, and processing quality of spring wheat grain, as well as nitrogen accumulation, remobilization, and assimilation from 2020 to 2022. Our results showed that reduced chemical nitrogen input decreased nutrition production, but green manure could increase protein and starch yields of wheat grain. HCVN2 (mixed hairy vetch and common vetch under 20% nitrogen reduction) displayed higher protein and starch yields, which increased by 35.9 and 16.2% compared to fallow after wheat harvest and conventional nitrogen application (FN3). Meanwhile, reduced chemical nitrogen decreased wheat grain quality, but green manure improved wheat grain quality. HCVN2 had higher wheat grain quality, which improved by 13.2 and 10.0% in essential amino acid and non-essential amino acid contents, enhanced by 20.0 and 22.2% in vitamin B and zinc contents, and increased by 14.0 and 8.6% in falling number and wet gluten compared to FN3, respectively. HCVN2 could simultaneously improve the nutritional production and quality of wheat grain. This was attributed to significantly increasing nitrogen accumulation and distribution in grain, enhancing the contribution rate of leaf, stem-sheath, and cob-glume nitrogen to grain nitrogen, and promoting the activities of nitrate reductase and glutamine synthetase, respectively. Therefore, mixed sown green manure under reduced chemical nitrogen by 20% was promising for improving nutrition production and quality of spring wheat grain by promoting nitrogen accumulation, remobilization, and assimilation.