Legume Genomics and Genetics 2025, Vol.16, No.6, 279-287 http://cropscipublisher.com/index.php/lgg 281 effectively absorb nutrients from the upper soil (Temperton et al., 2016). However, due to increased competition, plants will use more resources on the aboveground part, which may reduce the root system ratio and cause the roots to grow deeper (Rascher et al., 2018). In addition, the number of nodal roots and the unit root length will also change, which will affect the efficiency of water and nutrient absorption. Understanding the response of these roots is very helpful for breeding and field management, especially in different seeding densities, which can better improve yields. 3 Impact of Sowing Density on Soybean Yield 3.1 High-density sowing and its yield advantages and trade-offs When the planting is denser, the space between rows will become smaller, the leaves will cover more fully, the leaf area index will be higher, and light and nutrients can be used more thoroughly, so the total yield per acre can often be increased (Claupein et al., 2019). Experiments have found that when the density is high, the plants will grow taller and the first pod will be higher from the ground. This is especially true in plots with low yields or in systems where they are intercropped with other crops (Muguerza et al., 2023). However, the benefits come with costs: the number of pods and branches that can be grown per plant will decrease, the number of nodules and root dry weight will decrease, and the number of seeds per plant and overall vitality may also decrease (Guo et al., 2022a). Too high a density will also make the competition for water and fertilizer more intense, the quality of grains may decline, and the risk of lodging will increase. 3.2 Low-density planting and its role in resource use efficiency If the row spacing is widened and the plant spacing is enlarged, there will be less competition between plants, and each plant can grow more branches and pods, and more nutrients can be invested in root growth and nodule formation (Jańczak-Pieniążek et al., 2021). In high-yield areas with good conditions, this method can make up for the reduction in the number of plants by increasing the yield per plant, and resource utilization can be maintained or improved (Bittencourt et al., 2022). However, if the number of plants is so low that the sunlight and water and fertilizer in the soil are not fully used, especially in less than ideal environments, the total yield may drop. Low density also often improves some physiological indicators, such as chlorophyll fluorescence and root health, thereby improving grain quality. 3.3 Optimal density for maximizing yield under different climatic conditions The planting density that can maximize yield will vary depending on the local climate, soil, and management practices. In low-yield areas, higher density is required to achieve the highest yield; in high-yield areas, relatively lower density can be used because individual plants can make up for the yield by setting more seeds (Pospišil and Pospišil, 2024). For example, research in North America indicates that the agronomically optimal planting density increases by about 24% from high-yield to low-yield areas (Schmidt et al., 2019). In Northeast China, the density that can achieve the highest yield is about 45.4 × 10⁴ plants/hectare (Wang et al., 2023). In areas with short growing seasons and low temperatures, early planting and medium density can often adjust the canopy structure and drive yield increases (Huang et al., 2024). Therefore, the planting density must be adjusted according to the local climate and management conditions to optimize both yield and resource utilization (Ball et al., 2001). 4 Influence of Sowing Density on Seed Quality 4.1 Effects on protein and oil content of seeds Whether the density of planting is high or low will directly affect the nutritional content of the seeds. For example, in the case of crambe, high density will increase the crude fat (oil) and crude fiber content, but the total protein will decrease (Szatkowski et al., 2024). A similar phenomenon also occurs in peas: when the density is increased from 70 plants per square meter to 110 plants per square meter, the protein content in the seeds will also increase (Bobrecka-Jamro et al., 2023). These results show that oil is more likely to accumulate at high density, but the protein ratio may be diluted; the specific changes depend on the local climate and variety characteristics. 4.2 Relationship between plant spacing and seed uniformity Plant spacing, row spacing and density are tied together to determine whether the seed size is uniform. For white
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