Legume Genomics and Genetics 2026, Vol.17, No.1, 68-79 http://cropscipublisher.com/index.php/lgg 74 whereas in low-yield environments, increasing density helps maintain yield by compensating for reduced seed number per plant (Carciochi et al., 2019). Additionally, uniform spatial distribution of plants at higher densities reduces variability among individuals and improves overall yield stability (Xu et al., 2021). These findings highlight the importance of tailoring planting density to specific growing conditions to optimize both individual plant performance and total soybean productivity. 5.2 Responses of pod number, seed number, and 1000-seed weight Yield components such as pod number per plant, seed number per pod, and 1000-seed weight respond differently to changes in planting density. Generally, increasing planting density leads to a decrease in pod number per plant due to resource competition limiting branch development and reproductive capacity (Rahman et al., 2011). However, the total number of pods per unit area may increase or remain stable because of the greater number of plants compensating for fewer pods per individual. Seed number per pod tends to be less sensitive to density changes but can decline slightly under very high densities due to stress during pod development (Yang et al., 2025). The 1000-seed weight often decreases with increasing planting density as competition restricts assimilate availability for seed filling (Rahman et al., 2011). For instance, studies have shown that while seed weight declines at very high densities beyond 315,000 plants per hectare, moderate increases in density maintain or slightly reduce this parameter without severely impacting final yield. Cultivar differences also play a role; some genotypes maintain higher seed weights under dense planting due to better resource allocation strategies (Xu et al., 2021). Overall, optimizing planting density involves balancing these components—maximizing pod and seed numbers while minimizing reductions in seed weight—to achieve the highest possible grain yield. 5.3 Determination of optimal planting density range Determining the optimal planting density range is critical for maximizing soybean yield while maintaining resource use efficiency. Research indicates that optimal densities vary by region, environment, cultivar, and management practices but generally fall within a moderate-to-high range. In the Huang-Huai-Hai Plain region of China, densities between 270,000 and 315,000 plants per hectare produced the highest economic returns and seed yields by balancing source-sink relationships and improving pod-setting characteristics (Yang et al., 2025). Similarly, North American studies suggest that agronomic optimal plant density (AOPD) increases from high- to low-yield environments by approximately 24%, reflecting adaptation needs based on environmental constraints (Carciochi et al., 2019). Other investigations recommend densities around 80-100 plants per square meter (800,000-1 million plants per hectare) depending on variety and seasonality but emphasize that exceeding certain thresholds (e.g., above 315,000 plants/ha) may reduce individual plant performance without proportional gains in population yield (Rahman et al., 2011; Sacramento et al., 2020). Uniform spatial distribution combined with appropriate density further enhances light interception and dry matter accumulation leading to improved yields. Therefore, selecting an optimal planting density requires consideration of local conditions alongside cultivar traits to ensure sustainable soybean production with maximized yield potential. 6 Effects of Planting Density on Canopy Structure and Resource Use Efficiency 6.1 Changes in ventilation and light penetration within the canopy Planting density significantly influences canopy structure, which in turn affects ventilation and light penetration-key factors for photosynthesis and crop health. Increasing planting density generally raises the leaf area index (LAI) and canopy coverage, leading to greater interception of photosynthetically active radiation (PAR). However, denser canopies often reduce light penetration to lower leaves due to self-shading, which can limit photosynthetic efficiency in the lower canopy layers (Li et al., 2024). For example, optimizing row spacing in high-density soybean plantings improved canopy transmittance by creating a more favorable light environment that enhanced photosynthetic capacity and reduced excessive shading.
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