Effect of Different Nitrogen Rates and ApplicationTimes on Yield and Quality Criteria of Bread Wheat by Principal Component Analysis

This research was conducted at Bursa Uludag University, Faculty of Agriculture, during the 2022–2023 and 2023–2024 growing seasons to determine the effect of nitrogen applied at different times and doses on grain yield and quality in a bread wheat variety. The experiment was carried out using a split-plot design in randomized blocks with three replications. Fertilizer treatment times were assigned to the main plots (T1; T2; T3; T4; T5; T6; T7), and fertilizer doses were assigned to the subplots (N1: control, N2: 80 kg N, N3: 160 kg N, N4: 240 kg N ha−1). The characteristics examined included basic physiological indicators (SPAD meter values and flag leaf area), growth and vegetative characteristics (plant height and spike length), yield components (number of spikelets per spike, number of grains per spike, grain weight per spike), quality criteria (thousand-grain weight, hectoliter weight, and protein ratio), and grain yield characteristics. Analysis of variance (ANOVA) revealed statistically significant differences (p < 0.01) among treatment times, nitrogen doses, and their interactions for most of the characteristics examined in both seasons. The high nitrogen treatment (240 kg N ha−1) significantly increased physiological and agronomic parameters, including chlorophyll content (SPAD), flag leaf area, plant height, spike length, and the number of spikelets per spike. Average grain yield ranged from 3539 to 8039 kg ha−1 in the first year and 1167–4329 kg ha−1 in the second year, with the highest values recorded at the 240 kg N ha−1 treatment. Similarly, the protein ratio varied between 9.4 and 13.6% in 2022–2023 and 8.5–12.7% in 2023–2024, reaching its highest level at the 240 kg N ha−1 dose. In both growing seasons, the highest grain yield (8039 kg ha−1 and 4329 kg ha−1) and high protein ratio (13.6% and 12.4%) were obtained in plots where the 240 kg N ha−1 nitrogen dose was applied in three equal splits (1/3 at sowing, 1/3 at tillering, and 1/3 at heading; T7). Principal component analysis (PCA) successfully explained 73.6% of the total variation in the first season (PC1: 61.4%, PC2: 12.2%) and 77.1% in the second season (PC1: 67.2%, PC2: 9.9%), confirming that splitting nitrogen into three parts simultaneously optimizes both yield components and grain quality. Consequently, to maximize bread wheat yield and quality, a total treatment of 240 kg N ha−1 split equally into sowing, tillering, and heading stages is recommended instead of traditional two-split treatments.