Optimization strategies for mitigating nitrogen loss in the aerobic composting of pig manure and microbial changes revealed by metagenomic analysis

In this research, comprehensive optimization strategies for mitigating nitrogen loss in pig manure compost was screened out and nitrogen cycle microbial changes revealed by metagenomic technology. Results showed the optimum combination of process conditions as C/N ratio of 25, turning frequency of twice/day, addition of biochar and inoculation with nitrogen retaining microbial agent. The nitrogen loss rate of the optimized group was 14.67%, which was 45.33% significantly lower than that of the traditional group. NH3, N2O, and NO emission significantly decreased by 42.74%, 48.93%, and 69.95%. Metagenomic analysis revealed that process optimization could change the microbial community, functional genes and metabolism pathways of the nitrogen cycling in the composting process. Nitrogen loss was mainly mitigated by increasing the enzyme activities in nitrogen assimilation (increased by 11.80%), nitrification (increased by 39.35%), and nitrogen fixation pathways (increased by 74.72%) and reducing the enzyme activities in denitrification pathways (decreased by 35.20%). The findings provided reference markers for further exploration of compost nitrogen loss. This comprehensive optimization strategies method for mitigating nitrogen loss was recommended in aerobic composting of pig manure.