Legume Genomics and Genetics 2024, Vol.15, No.6, 280-290 http://cropscipublisher.com/index.php/lgg 282 2.3 Competition for space in crops Competition for space among soybean plants primarily involves competition for water, light, and nutrients. High plant density can lead to intense competition for these resources, which can affect plant growth and yield. For example, increased plant density can enhance canopy light interception but may also lead to reduced individual plant growth due to competition for light (Xu et al., 2021). Similarly, competition for water and nutrients can be more intense at higher densities, potentially leading to nutrient deficiencies and reduced nodulation (Luca et al., 2014). Mechanisms of competition include shading, which reduces light availability to lower leaves, and root competition, which limits water and nutrient uptake. Studies have shown that non-uniform temporal distributions of plants can significantly reduce yield due to increased variability in plant growth and reproductive partitioning (Masino et al., 2018). This suggests that managing plant density and ensuring uniform plant distribution are crucial for optimizing resource use and maximizing yield. Additionally, the choice of planting density can influence physiological responses such as leaf area ratio and specific leaf area, which in turn affect biomass production and yield (Gan et al., 2002). 3 Effects of Soybean Plant Density on Growth and Yield 3.1 Relationship between photosynthesis efficiency and plant density Optimizing plant density is crucial for enhancing photosynthesis efficiency in soybean crops. Higher planting densities have been shown to significantly increase canopy light interception, which in turn boosts the photosynthetic rate and dry matter accumulation. For instance, a study demonstrated that increasing planting density from 1.8×105 to 2.7×105 plants ha⁻¹ led to a 22.8% increase in seed yield due to improved light capture and uniform plant spacing (Xu et al., 2021). This indicates that optimal plant density can enhance the overall photosynthetic efficiency of the soybean canopy, thereby improving yield. Moreover, lower plant densities can also have a positive impact on photosynthesis by reducing inter-plant competition for light, water, and nutrients. A study conducted in southern Brazil found that reducing plant density to 80 000 plants ha⁻¹ increased nodulation and photosynthesis per plant, although the overall yield was slightly reduced in one of the three cropping seasons (Luca et al., 2014). This suggests that while higher densities improve canopy-level photosynthesis, lower densities can enhance individual plant photosynthesis efficiency. 3.2 Changes in plant morphological characteristics Plant density significantly affects the morphological characteristics of soybean plants, including plant height, branch number, and leaf area index (LAI). Higher plant densities generally lead to taller plants with fewer branches and a higher LAI. For example, a study found that increasing plant density resulted in taller plants but reduced the number of branches per plant, which can affect the overall yield components (Moreira et al., 2015). This morphological adjustment is a response to increased competition for light, prompting plants to grow taller to capture more sunlight. Conversely, lower plant densities allow for more branching and a lower LAI, which can be beneficial for certain growth stages. Another study highlighted that lower densities resulted in increased nodulation and biomass production per plant, although the total yield per hectare was lower compared to higher densities (Luca and Hungria, 2014). This indicates that while higher densities optimize light capture and photosynthesis at the canopy level, lower densities can enhance individual plant growth and development. 3.3 Density effects on yield performance Balancing group competition and individual plant yield is a critical aspect of optimizing soybean yield under varying plant densities. Higher plant densities often lead to increased competition among plants, which can reduce the yield per individual plant but increase the overall yield per unit area. For instance, a study reported that higher plant densities significantly increased the field biomass yield and seed yield per unit area, despite reducing the yield per individual plant (Gonyane and Sebetha, 2021). This suggests that higher densities can maximize total yield by optimizing space utilization and light interception.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==