Managing the yield-quality trade-off through nitrogen management in modern winter wheat grown on Andisols

Balancing grain yield with end-use quality continues to be a challenge in high-yield wheat systems, as larger grain volumes tend to dilute protein content and diminish flour quality. Late nitrogen (N) application has been proposed to improve grain protein concentration and dough rheological quality without compromising yield; however, its effectiveness in high-organic-matter Andisols with strong N-buffering capacity remains poorly understood. Field experiments conducted over two growing seasons evaluated two winter wheat cultivars under increasing N rates (0-300 kg N ha -1 ) applied as conventional split fertilization, a modified split at equivalent total N, and late N supplementation at booting. Grain yield and yield components, flag-leaf photosynthetic activity during grain filling, and dough rheological properties were measured. Grain yield responded quadratically to N supply, plateauing at approximately 200-250 kg N ha -1 , with no significant differences in optimal N requirements among fertilization strategies. In contrast, grain protein concentration, wet gluten content, and alveograph parameters, including dough strength (W) and the P/L ratio. continued to improve beyond the yield plateau. Higher N availability during grain filling sustained net CO 2 assimilation and PSII maximum quantum yield (Fᵥ/F m ), indicating delayed flag-leaf senescence and cultivar-specific physiological responses. In highly mineralizing Andisols, grain yield becomes sink-limited at optimal N supply, while dough rheological quality remains source-driven and closely connected to post-anthesis physiological activity. These results indicate that yield and quality respond through partially decoupled mechanisms and should be considered as complementary yet distinct goals when developing N fertilization strategies for high-yielding wheat systems on volcanic soils. • Grain yield plateaued at 200-250 kg N ha -1 across fertilization strategies • Grain protein and dough rheology increased beyond the yield plateau • High post-anthesis N sustained photosynthetic activity during grain filling • Grain quality remained source-driven while yield was sink-limited