Appropriate nitrogen (N) management system is essential for effective crop productivity and minimizing agricultural pollution. However, the underlying mechanistic understanding of how N fertilizer regulates crop yield via soil properties in soils with different fertilities remains unresolved. Here, we used a field experiment that spanned 3 cropping seasons to evaluate the grain yield (GY), aboveground biomass and N recovery efficiency (NRE) after treatment with five N fertilizer application rates (N0, N75, N112, N150, and N187) in soils with three levels of fertility. Our results indicated that the highest GY across low, moderate, and high fertility soils were 1.5 t hm^-2 (N150), 4.9 t hm^-2 (N187), and 5.4 t hm^-2 (N112), respectively. The highest aboveground biomass and NRE were observed at N150 for all three levels of soil fertility, while only the N uptake by aboveground biomass of low and high fertility soils decreased at N187, confirming that excessive N fertilization results in a further decline in crop N uptake. The relationship between GY, NRE and N fertilizer application rates fit the unary quadratic polynomial model. To achieve a balance between grain production and environmental benefits in N fertilizer, appropriate N fertilizer rates were determined to be 97.5 kg hm^-2, 140 kg hm^-2 and 131 kg hm^-2 for low, moderate and high fertility soils, respectively. Structural equation modeling suggested that GY was significant correlated with soil microbial biomass carbon (SMBC) and N directly in low fertility field, with SMBC directly in moderate fertility field, and via SOC and NO₃^–N in high fertility field. Therefore, a soil-based management strategy for N fertilizers could enhance food security while reducing agricultural N fertilizer inputs to mitigate environmental impacts.

Appropriate deep application of fertilizer is the key basis for improving nitrogen use efficiency (NUE). However, the effects of different deep application methods and fertilizer types on nutrient migration, NUE and biomass in wheat season are unclear. Therefore, in this study, a barrel planting test with multilayer fertilization (¹⁵N labeled urea (U) and coated urea (CU)) was conducted in a long-term positioning trial of winter wheat in the North China Plain (NCP). We quantified the migration of fertilizer N (N_dff) in soil–plant–atmosphere and its effects on wheat biomass and NUE based on surface (U_sur, CU_sur), layered-strip (U_str, CU_str) and layered-mix fertilization (U_mix, CU_mix) of U and CU. Compared with surface fertilization, the concentration of mineral N in root zone (0–40 cm) was increased by U_str and U_mix (8.6–50.3%), and the concentration of ammonium N was decreased by CU_str and CU_mix (49.6–76.0%), but there was no change in the nitrate N. The biomass and total N absorption of wheat tissues (straw and root) were increased by 12.3–38.9% under U_str and CU_str. Meanwhile, the distribution of N_dff in the 0–10 cm soil was decreased under U_str and CU_str, but it was increased in the 10–30 cm soil, thereby promoting the absorption of N_dff in wheat tissues by 12.3–28.7%. The rates of absorption and loss of N_dff were the highest (57.6–58.5%) and the lowest (4.5%) under U_str and CU_str, respectively, compared with other treatments. Consequently, layered-strip fertilization optimized the migration and utilization of N_dff within the soil–plant–atmosphere system. This approach equalized distribution, enhanced absorption and minimized losses of N_dff, resulting in an increase in NUE by 9.6–16.7%. Under the same treatment, CU was more suitable for crop nutrient requirements than U, which was more conducive to the improvement of NUE. Our findings will provide a scientific basis for the precise directional fertilization of winter wheat in the NCP.