Beneficial effects of bacterial agent/bentonite on nitrogen transformation and microbial community dynamics during aerobic composting of pig manure

This study investigated the effects of adding a bacterial agent (B) and bentonite (BT) on nitrogen transformation, nitrogen functional genes, and the microbial community dynamics during the aerobic composting of pig manure, as well as their contributions to NH3 and N2O emissions. Treatments B, BT, and BT+B reduced the NH3 emissions by 31.34%, 18.82%, and 23.67%, respectively, and the N2O emissions by 53.16%, 72.56%, and 63.41%. N2O and NH3 emissions were strongly related to the functional genes. Adding bacterial agent promoted the ammonia oxidation process to reduce NH3 emissions, whereas the influence of bentonite on nitrogen conversion was mostly related to nirS and nirK in denitrification processes. Nitrification and denitrification were dominated by different functional microorganisms in various stages of composting, where Proteobacteria comprised the most important denitrifying microorganisms. Thus, the additives reduced NH3 and N2O emissions by regulating nitrification and denitrification processes, and adding both was highly advantageous.