Integrated soil–water–nitrogen management enhances dryland wheat productivity through coordinated root–canopy regulation

Dryland wheat production on the Loess Plateau is limited by low soil fertility and asynchronous water and nitrogen (N) supply. However, it remains unclear how integrated soil–water–N management coordinates aboveground–belowground growth. A three–year field experiment (2022–2025) evaluated six treatments: no fertilization (CK), local farmers' practice (FP), slow–release fertilizer (SRF), N topdressing (TN), organic manure with N topdressing (M+TN), and organic manure with N topdressing and supplementary irrigation at regreening (M+TN+I). This study assessed the effects of different management practices on grain yield, water productivity, and N use efficiency, and clarified the root–canopy pathways supporting high–yielding dryland wheat. We found that M + TN + I produced the strongest and most stable yield response. Compared with the FP, M + TN + I increased three–year mean grain yield by 28%, plant N accumulation by 39%, root biomass in the 0–40 cm soil layer by 46%, and soil NO 3 − -N storage at anthesis by 64%, while reducing the root–to–shoot ratio by 11%. Structural equation modeling indicated that soil NO 3 − -N storage was positively associated with grain yield indirectly through root biomass in the 0–40 cm soil layer, leaf area index, and dry matter accumulation and remobilization. In contrast, SRF and TN produced weaker or less consistent yield responses, indicating that changing fertilizer release or N timing alone was insufficient to sustain N availability and root–canopy coordination under dryland moisture constraints. Overall, integrated soil–water–N management improved wheat productivity through the combined effects of increased organic N input, improved soil water and N availability, and enhanced root–canopy coordination. Therefore, M + TN + I provides a practical strategy for sustainable intensification of dryland wheat production.