Soybean Growth Management: Post-emergent Herbicides and Mechanical Pruning as Tools to Optimize Cultivar Yield

Plant growth regulation has proven to be a promising strategy to optimize soybean yield performance, especially under varying planting densities. This study aimed to evaluate the effects of post-emergence herbicide application compared to mechanical pruning on the development and yield of soybean grown under two plant population densities. The experiment was carried out under field conditions during the 2021/2022 growing season on a farm located in Ipameri, Goiás, Brazil. A randomized block design was used in a 5 × 5 × 2 factorial arrangement with four replications. Treatments consisted of five intact technology soybean cultivars (providing pest protection and herbicide tolerance—RR2 PRO® or Xtend® 2) with indeterminate growth habit (Tormenta CE, M8372 Ipro, ST 797 Ipro, M7739 Ipro, and BMX Bônus Ipro), combined with five pruning alternatives: the application of three growth-regulating herbicides (2,4-D; imazethapyr; and lactofen), a mechanical pruning treatment, and a control without pruning. Each cultivar was evaluated under two plant population densities (recommended and 30% higher). Agronomic traits were assessed at harvest. Data were subjected to analysis of variance, and means were compared using Tukey’s test at a 5% significance level. The results showed that lactofen application (400 mL ha−1) significantly improved grain yield and controlled plant height across all cultivars and planting densities. For instance, the Tormenta CE cultivar under mechanical pruning yielded 6.092,67 kg ha−1 at the recommended population and 5.400,00 kg ha−1 at the higher density. In contrast, imazethapyr reduced yield, and the application of 2,4-D resulted in plant death in all cultivars except Tormenta CE. Mechanical pruning was less effective in controlling plant growth, especially at higher densities. These findings suggest that lactofen is a viable strategy for modulating soybean growth, improving productivity, and facilitating crop management, regardless of cultivar or planting density.