Triticeae Genomics and Genetics, 2025, Vol.16, No.2, 92-100 http://cropscipublisher.com/index.php/tgg 94 more dry matter and improve the utilization efficiency of nitrogen (Dai et al., 2014; Dong et al., 2020). Increasing density can to some extent compensate for the impact of insufficient nitrogen fertilizer, but if the nitrogen or density is too high, crops will distribute more nutrients to the stems and leaves, which will instead affect grain development and lead to a decline in yield and quality (Zheng et al., 2022). Only by finding the appropriate density and nitrogen fertilizer dosage can the maximum accumulation of dry matter be achieved, and nutrients be effectively distributed to the grains, thus realizing high yields and efficient resource utilization. 3 Effects on Root Architecture and Resource Uptake 3.1 Root length density and rooting depth under different sowing densities After the sowing density increases, the root length density (RLD) of the population will increase, especially in the upper soil layer. This is because when the density is high, more node roots will grow in each plant and each plot (Wang et al., 2024). After the density increases, the number of roots in the deep soil (such as 0.8 to 1.2 meters) will also increase, enabling crops to absorb more water and nutrients from the deep layers (Dai et al., 2014; Dong et al., 2020). However, although the number of roots in the entire plot has increased, the root systems of individual plants may become smaller. 3.2 Nitrogen-driven changes in root morphology and function Nitrogen application can promote better root growth, increasing both the length and weight of roots, especially in the topsoil (Mehrabi et al., 2021). If more nitrogen fertilizer is used, the surface area of the roots and the number of root tips will also increase, and the absorption capacity will be stronger (Zhang et al., 2021). Nitrogen can also affect the functions within roots, such as altering the activities of nitrate reductase and glutamine synthase, which are related to the absorption and transformation of nitrogen (Tian et al., 2024). However, the effect of nitrogen is also influenced by soil moisture and planting methods. 3.3 Combined impact on water and nutrient absorption efficiency When the sowing density and nitrogen fertilizer combination are reasonable, the root system of wheat will be more developed and can absorb water and nutrients from more layers of soil. For instance, if the row spacing is increased or the sowing method is improved, the number, length and surface area of roots will all increase, especially in deep soil. This can enhance the absorption efficiency of nitrogen without affecting the yield (Zheng et al., 2023). These practices can enhance the utilization rate of nitrogen fertilizers, maintaining or even increasing yields while reducing fertilization, which is beneficial for the sustainable cultivation of wheat. 4 Results and Analysis of Yield Performance 4.1 Grain yield response under varying sowing densities When the sowing density increases, the number of ears in the field will rise and the yield will generally increase, especially when nitrogen fertilizer is used appropriately. However, too high a density can cause problems. The number of grains on each spike may decrease, and the 1000-grain weight will also decline. The grain filling is not good enough, and the middle spikelets are most affected (Liu et al., 2020). Generally speaking, a medium-high density (300 to 400 grains per square meter) is the most likely to achieve high yields. If the density is further increased, the output will not only fail to rise but may even decline (Sun et al., 2023). 4.2 Nitrogen-use efficiency and yield correlation If nitrogen fertilizer is used well, the yield of wheat can be increased and the quality of the grains will also be better. However, if too much is applied, not only will the yield not increase, but the utilization efficiency of nitrogen fertilizer will also decrease. Some studies have found that when the sowing density is high, less nitrogen fertilizer can be applied, but the yield and utilization efficiency can still be maintained at a good level. This is because of its high density, which leads to a larger root system and better absorption of nitrogen from the soil (Dong et al., 2020; Zhou et al., 2024). Generally speaking, it is a reliable approach to apply nitrogen fertilizer in several portions and keep the total amount at 100 to 200 kilograms per hectare. This method can stabilize the yield, increase the protein content, and at the same time have a small impact on the environment (Jarecki, 2024; Lachutta and Jankowski, 2024).
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