Optimized sowing rate and fertilization regulate photosynthetic characteristics, grain yield and quality of winter wheat

The Loess Plateau is a principal dryland winter wheat production region in China, where unreasonable sowing rate and fertilization management limit yield and quality. A two-factor split-plot experiment was conducted during 2019–2021 with three sowing rates (150 kg ha −1 , 180 kg ha −1 , 210 kg ha −1 ) and three fertilization type (CK, OPT, OPT-N). Increasing sowing rate to 210 kg ha −1 significantly improved population tiller, secondary root number, and canopy structure. OPT reduced N input by > 50% but maintained plant growth and delayed leaf senescence. The 180 kg ha −1 rate enhanced canopy light interception at anthesis, while 210 kg ha −1 better sustained post-anthesis chlorophyll content, net photosynthetic rate, and stomatal conductance. Compared with OPT, OPT-N markedly restricted root growth, photosynthesis, and matter accumulation. 210 kg ha −1 + OPT significantly increased 1000-grain weight by 5–11%, grain yield by 1.7–3.7%, total starch by 1.91–5.22%, and flour processing quality. The interaction significantly regulated growth, photosynthesis, yield, and quality. This study demonstrates that 210 kg ha −1 + OPT realizes synchronous improvements in yield, quality, and resource efficiency under reduced N input, providing a green cultivation model for dryland wheat.