Patterns of crop-specific fertilizer-nitrogen losses and opportunities for sustainable mitigation: A quantitative overview of 15N-tracing studies

Understanding crop-specific fertilizer-nitrogen (N) loss patterns, driving factors, and mitigation potentials is vital for developing efficient mitigation strategies. However, analyses based on the gross magnitude of fertilizer-N losses within a growing season remain fragmented and inconclusive at a global scale. To address this gap, we conducted a global meta-analysis using 940 observations from 79 published 15N-tracing studies to assess the effects of natural factors, soil parameters, and N application rates on gross fertilizer-N losses in cereal-cropped soils. We found that China had the highest conventional fertilizer-N application and loss rates (230-255 and 75.9-114 kg N ha−1 season−1, respectively) and the lowest soil organic carbon (SOC) contents (10.6 g kg−1) among the countries examined. Mean annual precipitation, SOC content, and soil pH were key parameters affecting fertilizer-N losses in wheat-, maize-, and rice-cropped soils, respectively. Fertilizer-N application rates were positively correlated with N loss amounts, while higher SOC levels led to lower losses. Adopting optimized N application rates combined with improving SOC levels could potentially mitigate 34.8%-59.6% of N losses without compromising crop yields compared with conventional practices. This study underscores the critical role of SOC in reducing N losses and suggests that future research should focus on innovative strategies and efficient organic amendments for enhanced SOC sequestration.