Effects of two strains of thermophilic nitrogen-fixing bacteria on nitrogen loss mitigation in cow dung compost

Excavating nitrogen-fixing bacteria with high-temperature tolerance is essential for the efficient composting of animal dung. In this study, two strains of thermophilic nitrogen-fixing bacteria, NF1 (Bacillus subtilis) and NF2 (Azotobacter chroococcum), were added to cow dung compost both individually (NF1, NF2) and mixed together (NF3; mixing NF1 and NF2 at a ratio of 1:1). The results showed that NF1, NF2, and NF3 inoculants increased the total Kjeldahl nitrogen level by 38.43%-55.35%, prolonged the thermophilic period by 1-13 d, increased the seed germination index by 17.81%, and the emissions of NH3 and N2O were reduced by 25.11% and 42.75%, respectively. Microbial analysis showed that Firmicutes were the predominant bacteria at the thermophilic stage, whereas Chloroflexi, Proteobacteria, and Bacteroidetes were the predominant bacteria at the mature stage. These results confirmed that the addition of the isolated strains to cow dung composting improved the bacterial community structure and benefited nitrogen retention.