Molecular Soil Biology 2025, Vol.16, No.5, 265-271 http://bioscipublisher.com/index.php/msb 266 2 Effects of Nitrogen on Wheat Yield Formation 2.1 Regulation of growth stages and leaf area index by nitrogen Nitrogen fertilizer directly affects how wheat grows. After applying nitrogen fertilizer, the leaves are greener, photosynthesis is stronger, the leaves age slower, and the leaves grow larger, so that the leaf area index (LAI) will also increase, which will eventually help to increase dry matter mass and yield (Figure 1) (Hong et al., 2021; Noor et al., 2023). During the wheat booting or flowering period, if the amount of nitrogen fertilizer is appropriate, the photosynthetic efficiency of the leaves will increase, which can increase biomass and increase grain yield (Luo et al., 2021). In addition, nitrogen fertilizer can make the plants taller, the leaves are more and larger, and it is easier to absorb sunlight, which is very helpful to increase yield. Figure 1 (A) Maturity stage of greenhouse winter wheat. (B) Jointing stage of greenhouse winter wheat (Adopted from Noor et al., 2023) 2.2 Role of nitrogen in root development and nutrient uptake Nitrogen fertilizer also has an effect on the root system. Only when the roots grow well can they absorb more water and nutrients, which is very critical to increasing yield (Li et al., 2024). If fertilization is done properly, the aboveground part of the plant can grow faster and the nitrogen content in the grain will increase. However, if too much nitrogen is used, the dry matter and nitrogen may not be transported from flowering to maturity, and the yield will decrease instead of increase, and the fertilizer will be wasted. In addition, nitrogen fertilizer can also allow wheat to better utilize the nitrogen originally remaining in the soil, which can not only increase yield but also not cause too many environmental problems (Xu et al., 2020). 2.3 Varietal differences in yield responses to nitrogen Different wheat varieties also perform differently after using nitrogen fertilizer, which is related to their genetic characteristics and ability to absorb and utilize nitrogen (Walsh et al., 2022). Some varieties respond particularly well to a certain nitrogen fertilizer, such as urea and nitrate nitrogen mixed application. This combination is very effective in improving yield and nitrogen use efficiency (Cui et al., 2023). Moreover, different environments, soils and management methods will also affect the effect of nitrogen application. Therefore, the specific fertilization should be determined according to local conditions and the varieties used, which will make it easier to increase the yield (Wang et al., 2023; Yokamo et al., 2023; Feyisa et al., 2024). 3 Influence of Nitrogen on Wheat Quality Traits 3.1 Protein accumulation and gluten strength Nitrogen fertilizer is important for increasing protein in wheat grains. It can increase the total protein in the grains and increase the content of some major proteins, such as alcohol-soluble proteins and gluten. These proteins affect gluten strength and also affect baking performance (Zörb et al., 2018). Generally speaking, if nitrogen fertilizer is used appropriately, such as foliar spraying during flowering, the protein and gluten content can be increased. Moreover, varieties with low protein content are more sensitive to changes in nitrogen fertilizer (Iannucci et al., 2018; Gu et al., 2023). But this is not the case. Sometimes too much nitrogen absorption will reduce the gluten index, indicating that there may be a conflict between protein content and actual gluten quality (Chen et al., 2022).
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