Effect of Fertilization on Methane and Nitrous Oxide Emissions and Global Warming Potential on Agricultural Land in China: A Meta-Analysis

Anthropogenic greenhouse gas (GHG) emissions from croplands are primarily attributed to nitrogen (N) fertilization in agricultural production. However, the interactive effects of various agricultural management practices, climatic conditions, soil properties, and fertilization on non-CO2 GHG emissions (specifically methane (CH4) and nitrous oxide (N2O)) and gross global warming potential (GGWP) have been scarcely discussed. In this study, we conducted a meta-analysis of 326 agricultural treatments in China from 76 literature sources to elucidate the relationship between the response ratio (RR) of GGWP (GGWP RR), CH4 (CH4 RR), and N2O emissions (N2O RR) and various explanatory variables using redundancy analysis. Generally, nitrogen fertilizer application increased the N2O and CH4 emissions and GGWP by 120.0%, 32.5%, and 107.9%, respectively. We found that the GGWP RR was closely related to the rate of organic fertilizer application and initial bulk density, while it showed a negative association with the initial total soil nitrogen content. We found that CH4-RR was positively associated with the rate of synthetic fertilizer application, and N2O-RR exhibited a positive association with initial soil organic carbon and annual mean precipitation. Notably, the total fertilizer application rate had the most significant impact on both the GGWP RR and the N2O RR, while mean annual precipitation contributed the most to CH4-RR. Furthermore, a sensitivity analysis using a machine learning model suggested that the GGWP RR was more sensitive to synthetic fertilizer than to straw application, and reducing synthetic fertilizer by 30% from the current condition is likely to be the most effective way to alleviate the effect of fertilization on GGWP.