Reaction of Wheat Varieties to Additional Nitrogen Fertilization in the Climate Conditions of the Transylvanian Plain

Depending on soil nitrogen availability and soil–climatic conditions, nitrogen application at the boot stage in wheat can help maintain the photosynthetic activity of the upper leaves and support grain development and filling, thereby contributing to increased yield and protein content. This study examined the impact of nitrogen applied at the booting stage on grain yield, protein content, grain N uptake, and nitrogen use efficiency (NUE) of common winter wheat (Triticum aestivum L.) in Transylvanian Plain conditions. The experiment included eight consecutive crop seasons (2018–2026), four varieties (Andrada, Codru, Luminiţa, Georgiana), and two nitrogen doses: N50 and N100. In the N50- fertilization variant, 50 kg ha−1 nitrogen active substance was applied in autumn before sowing as basic fertilization and in the variant N100-, and other 50 kg ha−1 nitrogen was applied at the booting stage in addition to the base fertilization. The results showed that the additional fertilization of 50 kg N ha−1 at the booting stage, on top of the 50 kg N ha−1 applied before sowing, increased grain yield by an average of 763 kg ha−1 and grain protein content by 2.24 percentage points compared with the basic fertilization treatment (N50). The magnitude of the response varied among growing seasons and wheat genotypes. The calculated nitrogen use efficiency values also varied across genotypes and crop season, reflecting differences in crop response under the tested fertilization treatments. Since the experiment did not compare alternative nitrogen application timings at equivalent total nitrogen rates, the results should be interpreted specifically in relation to the additional nitrogen treatment evaluated in this study.