Research on the characteristics and driving factors of ammonia and greenhouse gas emissions during the application of livestock slurry

With the large-scale development of China's livestock and poultry breeding industry, the resource utilization of slurry has become a key link in the green transformation of agriculture. However, due to the lack of reasonable application methods during its return to the field, it is often accompanied by serious problems of ammonia volatilization (NH₃) and greenhouse gas emissions (N₂O, CH₄), which restrict the green and sustainable development of the industry. Due to limited sample size and regional background differences, existing studies often find it difficult to comprehensively analyze the complex mechanisms of gas emissions, resulting in insufficient generalizability of research conclusions. Therefore, this study aims to clarify the emission characteristics and driving factors of different types of livestock slurry application processes by integrating and reanalyzing gas emission related data. Based on 1057 experimental data from 103 global literature from 1989 to 2025, a meta-analysis was conducted using the SHAP value model to systematically quantify the effects of manure characteristics, natural factors, and application management on NH₃, N₂O, and CH₄ emission factors. The results showed that the type of slurry had a significant impact on N₂O emission factors, with the highest concentration of dry wet separated manure water (2.4%) and the lowest concentration of dry wet separated biogas slurry (0.5%); There is no significant difference in the emission factors of NH₃ and CH₄ among the overall types of slurry, but there are differences among different livestock and poultry. The main manifestation is that cattle slurry (such as dry wet separation biogas slurry NH₃ emission factor of 34.7%) has a more significant impact on NH₃ and N₂O emissions, while pig slurry has a more significant impact on CH₄ emissions (dry wet separation manure water CH₄ emission factor of 5.1%); By exploring the key driving factors of gas emissions during the application of slurry, it was found that the emission factors of NH₃, N₂O, and CH₄ emissions are dominated by different factors and have antagonistic effects, especially in terms of application management. The main manifestation is that the application method and nitrogen application rate have a positive effect on NH₃ emissions, while having a negative effect on N₂O and CH₄; From the response results of various gas emission factors to the characteristics of slurry, natural factors, and application management, it can also be seen that different factors, especially slurry characteristics and application management, have opposite effects on the emissions of NH₃ and N₂O. In terms of slurry characteristics, the NH₃ emission factor shows a trend of first increasing and then decreasing with changes in various indicators, while N₂O emission shows the opposite trend. In terms of application methods, compared to surface application (37.5%) and band spreading (17.7%), surface incorporation (10%) and injection application (13.8%) can significantly reduce NH₃ emission factors, but at the same time significantly increase N₂O emissions. By sorting and analyzing the gas data under the coupling conditions of slurry type and application method, a collaborative emission reduction strategy is proposed: When applying livestock slurry-urine mixtures, dry-wet separated manure water, and biogas slurry, the band spreading method exhibits significant advantages in emission reduction while also effectively controlling N₂O and CH₄ emissions. This study provides a scientific basis for the efficient return of slurry to the field and the development of emission reduction strategies, which helps promote the green and low-carbon development of agriculture.