A global meta-analysis of methane, nitrogen dioxide emission and soil organic carbon changes of grazing grassland soil under different grassland management

Exploring how methane(CH₄), nitrogen dioxide(N₂O) and soil organic carbon(SOC) content change under different grassland management is significant for mitigating global warming. We conduct a global meta-analysis to figure out the responses of CH₄, N₂O and SOC content to different management and Random Forest models are used to explore the most important driving factors of the changes. Our results show that grazing can cause SOC lose except in the climate zone Arid, which can increase the SOC content. The emission of CH₄ of grazing grassland increases under all grazing intensities and all climate zones. By comparison, the emission of N₂O decreases because of grazing activity except the light grazing intensity. As for fertilizer application, all types of fertilizers lead to more CH₄ and N₂O emission. Among all the fertilizers，cattle urine leads to the most soil N₂O emission and chemical fertilizer causes the most CH4 emission. When adding inhibitors, the mitigation effects are significant. They can decrease CH₄ and N₂O emission 35% and 25% respectively. As for the variables importance in grassland soil greenhouse gas emission, the results of Random Forest models show that the most three important variables in most models are initial SOC content, mean annual precipitation (MAP) and the mean annual temperature(MAT).This study highlights that moderate grazing is better for nature grazing grassland when considering the comprehensive mitigation effect and removing livestock excrement or adding inhibitors are effective ways to mitigate non-CO₂ greenhouse gas emission from soil.