Influence of different microbial inoculants on nitrogen retention and diazotroph community succession during cotton straw composting

Inoculation with microorganisms is an effective method for promoting compost maturity and quality. This study investigated the effects of different microbial inoculants on compost maturity, nitrogen retention, and the diazotroph community during cotton straw composting. Results revealed that inoculation improved organic matter degradation and compost maturity, increasing the total nitrogen masses by 6.6–33.0% and the total nitrogen by 84.6–112.1%. Particularly, the microbial inoculants containing Anoxybacillus rupiensis, Paenibacillus illinoisensis, and Bacillus velezensis (1:1:1, T1 treatment) exhibited the highest total nitrogen masses and total nitrogen content. Furthermore, inoculation enhanced nitrogenase activity and nifH abundance, and markedly influenced the succession of the diazotroph community, increasing their sensitivity to environmental variables during composting. Furthermore, the total nitrogen, C/N ratios, and moisture content significantly affected the diazotroph community. Results from a network analysis indicated that inoculation affected the co-occurrence patterns among the diazotroph species and increased complexity between diazotrophs. In conclusion, this study provided three promising microbial inoculants for high-quality compost production and a reference for promoting nitrogen retention in cotton straw composting.