Insight into mitigation mechanisms of N₂O emission by biochar during agricultural waste composting

The effects and mitigation mechanisms of biochar added at different composting stages on N₂O emission were investigated. Four treatments were set as follows: CK: control, B_B10%: +10 % biochar at beginning of composting, B_B5%&T5%: +5% biochar at beginning and + 5 % biochar after thermophilic stage of composting, B_T10%: +10 % after thermophilic stage of composting. Results showed that treatment B_B10%, B_B5%&T5%, and B_T10% reduced total N₂O emissions by 55 %, 37 %, and 36 %, respectively. N₂O emission was closely related to most physicochemical properties, while it was only related to amoA gene and hydroxylamine oxidoreductase. Different addition strategies of biochar changed the contributions of physicochemical properties, functional genes and enzymes to N₂O emission. Organic matter and C/N contributed 23.7 % and 27.6 % of variations in functional gene abundances (P < 0.05), respectively. pH and C/N (P < 0.05) contributed 37.3 % and 17.3 % of variations in functional enzyme activities. These findings provided valuable insights into mitigating N₂O emissions during composting.