Plant population: impacts on vegetative architecture, yield components, and grain yield
Plant population is one of the main management practices influencing soybean development and grain yield, particularly in modern cultivars with high phenotypic plasticity. This study evaluated the effects of different plant populations on yield components and grain yield of the soybean cultivar Brasmax Zeus IPRO under subtropical growing conditions. The experiment was conducted during the 2020/21 growing season in Dois Vizinhos, Paraná, Brazil, using a randomized complete block design with five plant populations (4, 6, 8, 10, and 12 plants m⁻¹) and four replications. Plant height, first pod insertion height, number of reproductive nodes, branches, pods, grains per plant, thousand-grain weight, and grain yield were evaluated. Plant height and thousand-grain weight were not significantly affected by plant population. Conversely, first pod insertion height increased linearly as plant density increased. Reduced plant populations promoted greater branching and significantly increased the number of reproductive nodes, pods, and grains per plant, demonstrating the strong compensatory growth capacity of soybean under low-density conditions. However, these morphological adjustments were insufficient to compensate for the lower number of plants per unit area. Consequently, grain yield increased linearly with plant population, with the highest yield (5,878.3 kg ha⁻¹) obtained at 12 plants m⁻¹, representing an increase of approximately 38% compared with the lowest population. The results demonstrate that although the soybean cultivar Brasmax Zeus IPRO exhibits considerable phenotypic plasticity, maintaining an adequate plant population is essential to maximize grain yield. Under the environmental conditions of this study, a population of 12 plants m⁻¹ (266,666 plants ha⁻¹) was the most suitable for achieving maximum productivity.