Mitigated nitrous oxide and ammonia emissions in the composting of tail vegetables by co-application of biochar and complex microbial agents: performance and microbial mechanisms

Introduction Aerobic composting is a mainstream strategy for harmless disposal and resource recycling of massive tail vegetables generated in the global vegetable industry. However, substantial emissions of nitrous oxide (N 2 O) and ammonia (NH 3 ), the dominant nitrogenous gaseous pollutants during composting, cause severe nitrogen loss, compromised compost fertilizer quality, and aggravated atmospheric pollution. To date, most nitrogen mitigation measures in composting are applied as single strategies, and the synergistic effect and underlying microbial mechanism of combined biochar and functional complex microbial agents on controlling N2O and NH3 emissions remain largely unclear. Methods In this study, four treatments were established to explore the effects of different amendments on nitrogen dynamics during tail vegetable composting: additive-free control (CK), single biochar amendment (BC), single inoculation with a homemade ammonia-oxidizing and cellulose-degrading complex microbial agent (M), and co-application of biochar and the microbial agent (BCM). Results The results showed that BCM exerted a prominent synergistic effect, achieving the maximum reduction in cumulative NH 3 (78.76%) and N 2 O (28.66%) emissions, with the highest inorganic nitrogen retention in the final compost across all treatments. Microbial analysis revealed that BCM significantly enriched key nitrifying Ureibacillus and nitrogen-fixing Paenibacillus, enhanced the complexity and stability of the microbial co-occurrence network, and identified keystone species with dual lignocellulose degradation and nitrogen transformation functions. Redundancy analysis confirmed pH as the key driver shaping nitrogen-transforming bacterial communities. Discussion This study provides a promising technical approach to mitigate full-process compost nitrogen loss and improve product quality, with important implications for sustainable vegetable waste management.