A quantitative synthesis of carbon and nitrogen losses during animal and poultry manure composting: drivers, pathways, and mitigation

Animal and poultry manure can be recycled through aerobic composting, but reported carbon (C) and nitrogen (N) losses are quite high. A global-scale study is needed to explore the main factors driving C and N losses and the technologies used to mitigate them. This study includes 117 peer-reviewed research articles, encompassing 492 treatments, for a meta-analysis. Overall, 45% of initial total carbon (TC) and 28% of initial total nitrogen (TN) were lost during composting. For N, NH₃-N volatilization was the dominant pathway, accounting for 16%, while N₂O-N accounted for 1.2% of initial TN. CO₂-C was the dominant pathway for C loss, accounting for 34%, and CH₄-C contributed 0.7% of initial TC. Furthermore, only NH₃-N-based emissions were significantly influenced by both composting method and scale. Moreover, applying chemical, physical, and microbial additives during composting reduced CH₄, CO₂, NH₃, and N₂O by 49%, 6.8%, 27.6%, and 30%, respectively. Compost piles covered with membranes and organic materials effectively reduced CH₄ and N₂O emissions, whereas negative-pressure aeration significantly reduced ammonia volatilization. In brief, low-emission manure composting requires integrated regulation of feedstock composition, C/N ratio, moisture content, and maximum temperature, along with targeted additive application. Furthermore, future composting studies should focus on applying mixed additives as mitigation strategies to reduce greenhouse gas (GHG) emissions and ammonia volatilization, as meta-analysis results show that these are effective in reducing nitrogen and carbon losses during aerobic composting.