Effects of different nitrogen application rates on photosynthetic characteristics and grain filling in wheat cultivar ‘Zhengmai 1860’

This study aimed to investigate the optimal nitrogen (N) application rate for the high-yield and high-quality cultivation of wheat and to enhance the N fertilizer use efficiency. The wheat cultivar ‘Zhengmai 1860’ was planted with four N application treatments: 0 (N0), 90 (N1), 180 (N2), and 240 kg·hm⁻² (N3). The effects of different N application rates on the photosynthetic characteristics, grain filling process, and yield components of wheat were analyzed. The results demonstrated that N application significantly influenced the photosynthetic characteristics, grain filling process, and yield formation of ‘Zhengmai 1860’. Appropriate N application significantly enhanced the efficiency of light energy capture and conversion by increasing the SPAD value and the activity of photosystem Ⅱ (PSⅡ) (F_v/F_m, maximal photochemical efficiency of PSⅡ; F_v/F₀, potential activity of PSⅡ; etc), thereby providing sufficient assimilates for grain filling. The two-year average data showed that compared with the N0 treatment, the N2 treatment increased the SPAD value, F_m (maximum fluorescence), F_v/F_m, and F_v/F₀ by 16.82%, 6.01%, 1.59%, and 10.08%, respectively. Moreover, the N2 treatment increased the maximum grain filling rate (V_max), the time to reach maximum grain filling rate (T_max), and the duration of grain filling (T) of ‘Zhengmai 1860’ by 11.16%, 4.81%, and 5.68%, respectively, compared with the N0 treatment, further promoting the increase in grain yield. Additionally, the durations of the gradual increase stage, rapid increase stage, and slow increase stage of grain filling (T₁, T₂, and T₃) and their corresponding average filling rates (V₁, V₂, and V₃) were all the highest under the N2 treatment. The N2 treatment resulted in the highest grain yield and 1 000-grain weight, with the grain yield 41.15%, 14.05%, and 11.42% higher than that under the N0, N1, and N3 treatments, respectively. The study indicated that a N application rate of 180 kg∙hm⁻² on the alluvial soil in the Huang-Huai Region was the optimal for ‘Zhengmai 1860’ to achieve the coordinated optimization of photosynthesis, grain filling, and yield under the experimental conditions. This finding can provide a theoretical basis for N-efficient cultivation of wheat in the Huang-Huai Region.