Mitigation of carbon and nitrogen losses during pig manure composting: A meta-analysis

Composting is a reliable way to recycle manure for use on croplands in sustainable agriculture. Poor management of the composting process can result in a decrease in the final compost quality and negative environmental impacts. Optimization technologies during composting have varied effects on the mitigation of carbon (C) and nitrogen (N) losses. To determine the feasibility and effectiveness of mitigation options, a meta-analysis was performed based on 68 studies in which C and/or N losses were investigated during pig manure composting. The results indicated that 48.7% of the total C (TC) was lost with 34.8% as CO₂-C and 0.9% as CH₄-C, and 27.5% of the total N (TN) was lost with 17.1% as NH₃-N and 1.5% as N₂O-N. The composting method and bulking agent type obviously influenced the C and N losses. CO₂-C and CH₄-C emission was significantly influenced by the initial C/N ratio and moisture, respectively. At the same time, NH₃-N and N₂O-N emissions were remarkably affected by the initial pH and composting duration, respectively. The results of the meta-analysis showed that TC and TN losses were reduced by 12.4% and 27.5%, respectively. Controlling feedstock, including the C/N ratio and moisture, could be regarded as N conservation technology. Controlling aeration, including turning frequency and ventilation rate, would be reliable in reducing greenhouse gas emissions. Applying additives, especially biochar and superphosphate, was found to be an effective method for synergistically mitigating C and N losses. Therefore, the production of high-quality compost products and minimization of environmental pollution will be achieved by a combination of adjusting the initial substrate properties, controlling the composting process conditions and applying additives.