Solid digestate biochar amendment on pig manure composting: Nitrogen cycle and balance.

Effect of solid digestate biochar (DB) on nitrogen cycle and balance was evaluated during composting by adding DB into mixtures of pig manure and Lycium chinensis branch filings. Results indicated that DB addition improved composting microenvironment and increased the total N content of the final product. Furthermore, N balance calculation indicated that the NH and NO emissions accounted for 72.14%-81.39% and 0.49%-2.37% of the total N loss without DB addition, respectively. After using DB, the N reductions in the form of NH and NO reduced from 10.78% to < 5.73% and from 0.34% to < 0.041% of total N, respectively. Addition of DB affected N fixation with 92.32%-93.67% of total N fixed in the compost than that of the T1 treatment (85.63%). DB amendment enhanced the aerobic bacterial communities and hindered anaerobic bacterial growth, thus benefiting the NH and NO emission mitigation and N conservation.