Strategy for nitrogen fertilizer substitution: Co-composting of agricultural waste to regulate vegetable quality and rhizosphere microorganisms.

Agricultural waste compost is being used as an alternative to traditional chemical fertilizers as an effective way to achieve sustainable agricultural development. In this study, a mixed compost derived from human faeces, livestock manure, and crop residues was used as a proportional replacement for traditional chemical fertilizers, and the mechanisms of its effects on pakchoi quality and soil rhizosphere microorganisms were systematically explored. The results showed that co-composting of agricultural waste effectively reduced the required amount of nitrogen fertilizer, with the combination of 40 % mixed compost + 60 % chemical fertilizer application (T60) yielding the highest pakchoi biomass and quality, notably increasing the fresh weight by 138.91 % and reaching a peak vitamin C content of 13.80 mg·100 g. In addition, the application of compost as a chemical fertilizer substitute changed the composition of the soil microbial community, with a greater impact on bacteria than fungi. Composting could improve the growth and quality indices of pakchoi by increasing rhizobacterial alpha diversity. Proteobacteria and Ascomycota are important microbial families that affect the growth and quality indicators of pakchoi, respectively. Functional analysis showed that the compost mainly regulated the growth and quality of pakchoi by upregulating the relative abundance of functional genes related to carbohydrate metabolism, lipid metabolism, and exogenous biodegradation and metabolism, as well as by increasing the abundance of symbiotic and saprotrophic fungi while decreasing that of pathotrophic fungi. This research can provide a foundation and theoretical support for the resource utilization of agricultural waste and the reduction of traditional chemical fertilizers.