Sowing date and seeding rate are key agronomic measures for regulating yield formation and quality accumulation in winter wheat, especially in the context of global warming, which has led to delayed sowing becoming the norm. Clearly identifying optimal combinations of sowing date and seeding rate under late-sowing conditions is crucial for achieving coordinated improvement in both high yield and quality. Therefore, this study used the strong-gluten wheat cultivar ‘Shaannong 33’ and conducted a two-factor split-plot field experiment in the southern North China Plain (Nanyang, Henan) during 2019–2021. Three sowing dates (early sowing: 27 October; intermediate sowing: 31 October–2 November; late sowing: 6–8 November) and four seeding rates (180 × 104, 240 × 104, 300 × 104, and 360 × 104 plants ha−1) were tested to systematically analyze the effects of sowing date and seeding rate on wheat yield and its components, grain processing quality, and starch physicochemical properties. The results showed that sowing from late October to early November (approximately 25 October to 2 November in 2019–2020 and 25 October to 31 October in 2020–2021) combined with a seeding rate of 240–300 × 104 plants ha−1 maintained yield at a comparably high level across both growing seasons while improving processing quality indicators such as protein content, wet gluten content, and dough stability time for the strong-gluten cultivar ‘Shaannong 33’. However, the optimal sowing window varied between years: in 2019–2020, both D1 (27 October) and D2 (2 November) produced comparable yields, whereas in 2020–2021, D2 (31 October) was superior for both yield and quality. This inter-annual variability highlights the influence of climatic conditions on the optimal sowing window. Further delaying the sowing date to after 6 November led to decreases in yield and quality parameters; however, increasing the seeding rate to 360 × 104 plants ha−1 partially compensated for yield loss. In addition, late sowing significantly increased amylopectin content, swelling power, and pasting indicators such as peak viscosity and final viscosity while decreasing amylose content and pasting temperature, which is beneficial for improving cooking and eating quality. Correlation analysis indicated that the amylose/amylopectin ratio was the core factor determining starch pasting properties, while protein content showed a significant negative correlation with starch pasting indicators, reflecting the resource competition effect between grain protein and starch. Yield differences between the two years were mainly driven by changes in spike number per unit area, while inter-annual climate fluctuations (especially precipitation and temperature) significantly affected spike formation capacity. Overall, sowing date and seeding rate have a synergistic regulatory effect on yield and quality of late-sown wheat for the strong-gluten cultivar ‘Shaannong 33’. It is recommended to adopt a sowing date of 25–31 October with the seeding rate controlled at 240–300 × 104 plants ha−1 to achieve synergistic improvement of yield and quality under late-sowing conditions in the southern North China Plain for this cultivar.
Li et al. (Mon,) studied this question.