Season-specific nitrogen management shapes soil microbial communities and crop productivity in wheat-maize rotation system.

Based on a long-term positioned field experiment in a wheat-maize double-cropping system, the regulatory mechanisms of nitrogen fertilizer legacy on soil-crop coordination and microbial functions remain unclear. A two-year field experiment was conducted with four treatments: CK: no N fertilizer applied during either wheat or maize seasons; W1M0: N carryover only during the winter wheat season; W0M1: N carryover only during the summer maize season; W1M1: N carryover during both wheat and maize seasons. Compared with the unfertilized control (CK), W1M0 and W0M1 increased average annual yields by 45.7% and 42.2%, respectively, while W1M1 increased by 58.6%. On average, W1M1 produced the highest yield (21.8 t ha-1), with W1M0 and W0M1 achieving 91.9% and 89.7% of W1M1 yield, respectively. fertilization increased the abundance of predicted chemoheterotrophic functions. W0M1 influenced predicted N-transformation functions and fungal guilds. Bacterial community composition responded more strongly than fungal communities. Soil-crop coupling coordination varied dynamically with growth stages and N management patterns. PLS-SEM revealed that soil nitrogen content from the preceding wheat season explained 97.5% of the variance in subsequent maize soil physicochemical properties, which was 2.65 times higher than the corresponding explanatory power of maize-season N (36.8%), indicating a stronger predictive legacy of wheat-season N application on soil-crop coordination. In conclusion, seasonal N coordination is more crucial than total N input. Leveraging the superior legacy effect of wheat-season N application provides a scientific basis for precise fertilization regulation in rotation systems.