A global meta-analysis of greenhouse gas emissions and carbon and nitrogen losses during livestock manure composting: Influencing factors and mitigation strategies

The management of manure composting contributes to alleviate the global greenhouse effect. To improve our understanding of this process, we conducted a meta-analysis of 371 observations from 87 published studies in 11 countries. The results showed that the difference in nitrogen content in feces significantly affected the greenhouse gas (GHG) emissions and nutrient losses of subsequent composting, with NH3-N, CO2-C, and CH4-C losses all increasing with its rise. Windrow pile composting (especially compared to trough composting) had lower GHG emissions and nutrient loss. C/N ratio, aeration rate, and pH value significantly affected NH3 emission, and a decrease in the latter two can reduce it by 31.8 % and 42.5 %, respectively. Decreasing the moisture content or increasing the turning frequency could decrease CH4 by 31.8 % and 62.6 %, respectively. The addition of biochar or superphosphate had a synergistic emission reduction. The emission reduction of N2O and CH4 by biochar was more prominent (44 % and 43.6 %), while superphosphate on NH3 (38.0 %) was better. And the latter was more suitable if added in 10-20 % of dry weight. Dicyandiamide was the only chemical additive (59.4 %) with better N2O emission reduction performance. Microbial agents with different functions had certain effects on NH3-N emission reduction, while the mature compost had a certain effect on N2O-N emissions (67.0 %). In general, N2O had the highest contribution to the greenhouse effect during composting (74.22 %).