Analysis of the Effects of Nitrogen Fertilizer on Wheat Yield and Quality Under Late-Sowing Conditions

Climate change and cropping-system adjustments have caused widespread delayed sowing, limiting wheat growth and yield. Although optimized nitrogen management can partially mitigate late-sowing stress, the optimal nitrogen rate and basal–topdressing ratio for late-sown high-quality wheat remain undefined, limiting the development of targeted cultivation strategies. To solve the above scientific problems and clarify the regulatory effects of nitrogen fertilizer application regimes on the yield and quality of late-sown wheat, a two-year fixed-field experiment was carried out in this study. The late-sowing-tolerant wheat cultivar Yangmai 25 was used as the material. With a sowing date of 25 November (delayed by 20 days compared to the optimal sowing period), a split-plot field experiment was carried out with two factors: nitrogen application rate (225 and 300 kg N·ha−1) assigned to the main plots, and basal–topdressing ratio among the basal-, tillering-, and jointing-stage fertilizer applications (7:1:2, 5:1:4, and 3:3:4) arranged in the sub-plots. The results showed that both the nitrogen application rate and basal–topdressing ratio comparison had highly significant effects on the grain yield of Yangmai 25. Under the same basal–topdressing ratio, increasing the nitrogen application rate from 225 to 300 kg·ha−1 improved the spike number and grains per spike, but reduced the 1000-grain weight and grain yield. Under the same nitrogen application rate, increasing the topdressing proportion improved the grain number per spike, 1000-grain weight, and yield, while the spike number decreased. Specifically, the 3:3:4 management strategy resulted in an average yield increase of 3.11% and 8.94% over two years compared to the 5:1:4 and 7:1:2 strategies, respectively. Both the nitrogen application rate and basal–topdressing ratio had highly significant effects on quality indicators, such as protein content, wet gluten content, sedimentation value, dough formation time, sodium carbonate solvent retention capacity (SRC), sucrose SRC, and other quality indicators, but had minimal impact on grain hardness, water absorption, and water SRC. Under the same nitrogen application rate, the basal–topdressing ratio of 3:3:4 significantly increased grain protein content, wet gluten content, sedimentation value, dough development time, and dough stability time compared to the 7:1:2 treatment. In addition, under the experimental conditions of this study, the 225 kg·ha−1 nitrogen application rate combined with the 3:3:4 basal–topdressing ratio achieved better comprehensive performance in the yield and quality of Yangmai 25 compared with that of the 300 kg·ha−1 treatment. Further experiments are required to determine the optimal nitrogen application rate for this cultivar under late-sowing conditions.