Determining effect of fertilization on reactive nitrogen losses through nitrate leaching and key influencing factors in Chinese agricultural systems

Nitrate leaching is the main pathway of reactive nitrogen loss in Chinese agricultural systems, leading to groundwater contamination. However, the effect of fertilization on reactive nitrogen losses through nitrate leaching under various natural conditions and key influencing factors in Chinese agricultural systems remains unclear. Therefore, we conducted a comprehensive meta-analysis of 394 observations from 50 published articles to investigate how management practices, climatic conditions, and soil properties influence nitrate leaching from upland and paddy fields in China. Our results showed that nitrogen fertilizer application (NFP) significantly increased nitrate leaching in paddy and upland fields, with paddy fields exhibiting lower nitrate leaching than upland fields. In paddy fields, soil pH and NFP timing were the main drivers of nitrate leaching, while in upland fields, NFP rate and pH were the main driving factors. The NFP rate showed a significant positive correlation with nitrate leaching in both upland and paddy fields. Combining chemical fertilizer and organic manure applications was the effective method for mitigating nitrate leaching in paddy and upland fields. The structural equation modeling (SEM) revealed significant effects of soil properties on the nitrate leaching in paddy and upland fields during the crop growing season (P<0.05), with standard path coefficients of -0.46 and 0.07, respectively. NFP in soil with organic matter (SOM) >= 30 g kg(-1) and total nitrogen (TN) of 1-2 g kg(-1) declined the risk of nitrate leaching in paddy and upland fields. Additionally, NFP in regions with mean annual air temperature (MAT) >15 degree celsius helped mitigate the risk of nitrate leaching. Our findings provide valuable guidance for optimizing NFP in agricultural production to improve nitrogen use efficiency and reduce groundwater pollution.