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 NH-N, CO-C, and CH-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 NH 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 CH by 31.8 % and 62.6 %, respectively. The addition of biochar or superphosphate had a synergistic emission reduction. The emission reduction of NO and CH by biochar was more prominent (44 % and 43.6 %), while superphosphate on NH (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 NO emission reduction performance. Microbial agents with different functions had certain effects on NH-N emission reduction, while the mature compost had a certain effect on NO-N emissions (67.0 %). In general, NO had the highest contribution to the greenhouse effect during composting (74.22 %).