Spatial divergence of nitrogen fate in China's wheat systems: a meta-analysis and machine-learning roadmap for region-specific management

Optimizing crop productivity while mitigating pollution requires a system-wide understanding of nitrogen (N) fertilizer fate and its loss pathways. However, regional variability in N fate and its linkage to yield response in China’s wheat systems remains poorly quantified. We collected 4077 observations to analyze the effects of N fertilizer management, climate, and soil properties on wheat yield, N fate, and reactive nitrogen (Nr) losses using meta-analysis and machine learning. At the national scale, wheat yield increased by 65.40% with N fertilization, with applied N partitioned into 41.56% uptake, 29.66% residual, and 38.81% losses. The Nr losses comprised NH 3 (9.35%), N 2 O (0.73%), NO (0.38%), leaching (7.38%), and runoff (4.68%). At the regional scale, N uptake exhibited an increasing trend from north to south, whereas N residual and N loss gradually decreased. NH 3 volatilization accounted for 91.76% of total N loss in northern China (NC). In central China (CC), NH 3 constituted 53.45% of the losses, with N leaching accounting for 41.38%. By contrast, southern China (SC) showed a more even distribution of losses across pathways. N application rate was the key determinant of N fate, whereas pH, mean annual precipitation, mean annual temperature, and bulk density had the greatest influence on Nr losses. Nationally, N uptake was the dominant driver of yield response, accounting for 54.06% of the variation. Regionally, uptake remained the key factor in CC (37.83%), whereas NC (27.33% uptake; 16.09% loss) and SC (15.20% uptake; 12.37% loss) showed substantial sensitivity to N loss. N residual had minimal impact in most regions but was significant in CC (11.66%). Enhancing nitrogen uptake is the top priority in increasing wheat yield across different regions of China, while the role of fertilizer N loss and residual regionally varied. Accordingly, N management should prioritize loss reduction in NC and SC, and residual management in CC. • Applied N partitions as 41.56% plant uptake, 29.66% soil residual, and 38.81% environmental loss in China’s wheat systems. • N uptake increases from north to south, while soil residual and environmental loss progressively decrease along this gradient. • Northern China loss dominates as NH 3 , Central features NH 3 and N leaching, and Southern shows balanced loss. • N rate governs overall fate, while regional climate and soil properties control specific loss pathways. • Regional nitrogen efficiency disparities directly affect yield stability, forming the basis for tailored management.