Effects of Different Mesotrione Residual Levels on Morphological, Physiological, and Yield Characteristics of Brassinosteroid-Treated Soya Bean (Glycine max L. Merr.)

Mesotrione is a herbicide used in field crops to control grass and broadleaf weeds worldwide. For grain crops such as maize, mesotrione is recommended for a waiting period of up to 24 months before planting. This research builds on earlier investigations that explored the influence of brassinosteroids on soybean and other legume species. Hence, the study aimed to determine the effects of mesotrione residues on morpho-physiological and yield parameters of a brassinosteroid-treated soya bean. The experiment was a pot trial, laid out in a completely randomized block design, arranged in a 4 × 2 factorial design. Mesotrione was applied at concentrations of 1.6 µg.ai kg−1 soil, equivalent to 45 days after application (DAA), 0.05 µg.ai kg−1 soil (90 DAA), and 0.0016 µg.ai kg−1 soil (135 DAA), with untreated plants as the control. With increasing concentration, symptoms ranged from bleaching and necrosis to higher concentrations. Furthermore, findings in this study suggest that the combination of mesotrione (at 0.0016 µg.ai kg−1) and recommended application rate of brassinosteroid plays an important role in improving nutrient uptake, resulting in increased plant growth, physiology, and yield. It could be concluded from the measured and visually observed parameters that mesotrione beyond 0.0016 µg.ai kg−1 concentration resulted in negative effects on the plant growth, physiology, and yield; thus, a mitigating strategy using eco-organic production systems with different levels of brassinosteroids to improve soya bean treated with mesotrione should be prioritized as a future study.