Water and nitrogen management strategies influence grain filling and yield of winter wheat in the North China Plain

Optimizing water and nitrogen inputs during wheat’s critical developmental stages is vital for improving winter wheat yield potential and ensuring food security in the North China Plain, where water resources are increasingly constrained. A 3-year field experiment (2019–2022 winter wheat growing seasons) was conducted under a drip irrigation system to evaluate the effects of three water-saving irrigation regimes on winter wheat yield formation: DI, irrigation and split nitrogen application at jointing, booting, anthesis, and medium milk stages; T J , a single irrigation and nitrogen application at jointing; and T JA , irrigation at jointing and anthesis with a single nitrogen application at jointing. The results showed that DI significantly increased grain yield compared with T JA and T J , primarily by enhancing thousand-grain weight and grain number per unit area without reducing spike number. The increased thousand-grain weight was associated with a higher leaf area index, enhanced antioxidant enzyme activities, reduced malondialdehyde accumulation, and sustained higher photosynthetic capacity during mid-to-late grain filling. DI also improved both the rate and duration of grain filling, particularly during the fast and slow phases, and increased grain size and favorable grain morphology (grain length, width, thickness, roundness, and seed area), thereby contributing to greater final grain weight. These findings demonstrate that coordinated water and nitrogen management at key developmental stages promotes both grain number formation and grain weight realization, providing an effective agronomic strategy to enhance wheat yield potential and resilience in areas with limited water resources.