Optimized Split Nitrogen Topdressing Under Micro-Sprinkler Fertigation Improves Wheat Yield and Quality via Grain Filling and Nitrogen Translocation

This study aims to elucidate the effects of split-topdressed nitrogen (N) via micro-sprinkling fertigation on grain filling and N translocation and overcome the bottleneck in the synchronous enhancement of yield-quality under traditional border irrigation with broadcast N application. Using Gaoyou 2018 (strong gluten) and Heng 4399 (medium gluten), four treatments were established: conventional border irrigation with N at jointing (I1), micro-sprinkler irrigation with N at jointing (I2), micro-sprinkler irrigation with N at jointing and anthesis (1:1; I3), and micro-sprinkler irrigation with N at jointing, anthesis, and 12 days after anthesis (DAA) (5:3:2; I4). Results showed that I4 achieved the highest grain yield (10,578.6 kg·ha−1; +9.6% average), primarily attributed to significantly increased thousand-kernel weight (TKW; +1.7–4.2 g). I4 accelerated mid-to-late filling, extended the active filling period, and increased final grain mass by 1.5–4.6 g. I4 promoted post-anthesis N uptake and its remobilization to grains, improving nitrogen uptake efficiency (NUpE). I4 elevated grain protein content (gliadin-to-glutenin ratio +6.0%), improved gluten characteristics, and enhanced bread-baking quality, with these advantages being more pronounced in the strong-gluten cultivar. Overall, I4 synergistically enhances grain yield and quality by optimizing grain filling and N translocation. This study provides a theoretical basis for mitigating N leaching and ammonia volatilization while implementing high-yielding, high-quality cultivation practices.