Legume Genomics and Genetics 2024, Vol.15, No.6, 280-290 http://cropscipublisher.com/index.php/lgg 283 However, extremely high densities can lead to excessive competition, negatively impacting both individual plant yield and overall productivity. A study found that while increasing plant density generally improved yield, densities beyond a certain threshold (e.g., 100 plants m⁻²) resulted in reduced seed yield due to excessive competition (Rahman et al., 2011). Therefore, finding the optimal balance between plant density and competition is essential for maximizing soybean yield. 4 Role of Nutrient Management in Soybean Growth 4.1 Key nutrient requirements for soybean Soybean plants require a balanced supply of essential nutrients to achieve optimal growth and yield. The primary macronutrients necessary for soybean development include nitrogen (N), phosphorus (P), and potassium (K). Nitrogen is crucial for protein synthesis and overall plant growth. It can be supplied through biological nitrogen fixation (BNF) or mineral fertilizers. However, excessive nitrogen fertilization can reduce BNF by up to 70% in greenhouse conditions and 44% in field conditions, particularly during the vegetative stage (Santachiara et al., 2019). Phosphorus is vital for energy transfer and root development, while potassium is essential for enzyme activation and water regulation. Studies have shown that soybean plants accumulate significant amounts of these nutrients, with 275 kg N, 21 kg P, and 172 kg K required per hectare to produce high yields (Bender et al., 2015). In addition to macronutrients, soybean plants also need micronutrients such as zinc (Zn), boron (B), and molybdenum (Mo). These micronutrients play critical roles in various physiological processes. For instance, foliar application of Zn and B has been shown to significantly improve pod formation and seed yield in semi-arid climates (Dass et al., 2022). The omission of these nutrients can lead to visible deficiency symptoms and reduced plant growth, as observed in nutrient omission trials in Western Kenya (Keino et al., 2015). 4.2 Nutrient management in different growth stages of soybean The nutrient demands of soybean plants vary significantly across different growth stages, including germination, flowering, and pod-filling stages. During the germination stage, the primary focus is on root development and early vegetative growth, which requires adequate phosphorus and potassium. Studies have shown that phosphorus and potassium uptake is critical during the early vegetative stages, with up to 100% of season-long potassium uptake occurring by the R5.5 stage (Gaspar et al., 2017). As the plants transition to the flowering stage, the demand for nitrogen increases to support rapid vegetative growth and the initiation of reproductive structures. Nitrogen fertilization during this stage can significantly improve shoot dry weights and overall plant biomass (Keino et al., 2015). However, excessive nitrogen application during the vegetative stage can reduce BNF, highlighting the need for balanced nutrient management (Santachiara et al., 2019). During the pod-filling stage, the nutrient demand shifts towards supporting seed development. This stage requires a continuous supply of nitrogen, phosphorus, and potassium to ensure high seed yield and quality. Studies have shown that foliar application of nutrients such as urea, NPK, and DAP during the pod initiation stage can significantly improve seed yield and water-use efficiency (Figure 1) (Dass et al., 2022). Additionally, adequate irrigation during this stage is crucial for nutrient uptake and overall plant health. 4.3 Nutrient management strategies Effective nutrient management strategies for soybean cultivation involve the application of both organic and inorganic fertilizers. Organic fertilizers, such as cattle bone meal hydrolysate, have been shown to improve soybean growth characteristics, nutrient content, and chlorophyll pigment concentration (Nieto-Monteros et al., 2023). These organic sources provide a slow-release form of nutrients, enhancing soil fertility and reducing dependency on synthetic fertilizers. Inorganic fertilizers, including urea, DAP, and NPK, are commonly used to meet the immediate nutrient demands of soybean plants. Foliar application of these fertilizers at critical growth stages, such as pod initiation, has been shown to significantly improve seed yield and economic returns (Dass et al., 2022). Additionally, the use of micronutrient supplements, such as zinc and boron, can further enhance plant growth and productivity (Keino et al., 2015).
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