Magnésio via foliar para atenuação de estresse fisiológico de herbicidas na soja Enlist

Abstract

Soybean (Glycine max (L.) Merrill) is one of Brazil's main crops, and the use of herbicide-tolerant cultivars, such as Enlist™ E3 soybean, facilitates weed management but can cause physiological stress that compromises productivity. Given this, the present study aimed to evaluate the effects of foliar application of magnesium (Mg) in mitigating the physiological stress caused by these herbicides in Enlist™ E3 soybeans. The study was conducted through three field experiments in Mato Grosso do Sul (Caarapó, Dourados, and Juti) during the 2024/2025 harvest in an area planted with Enlist™ E3 soybeans. It was conducted in a completely randomized design, in a 5 x 5 factorial scheme, with five doses of Mg (0, 50, 100, 150, and 200 g ha⁻¹), using magnesium sulfate as the source, and five herbicides, without weeding: glyphosate (1500 g a.e. ha⁻¹), 2,4-D choline salt (1000 g a.e. ha⁻¹), glufosinate (500 g a.e. ha⁻¹), and weeding. The experimental plots measured 3 × 5 meters. This allowed for an integrated assessment of the effects of herbicides and foliar fertilization on the Enlist™ E3 soybean crop. Physiological parameters, nutritional analysis of plant tissue, photosynthetic rate, stomatal conductance and transpiration, photosynthetic pigment content, nitrogen compounds, total sugars, and sucrose in the leaves were measured. Visual symptoms of phytotoxicity and final grain yield were also evaluated. The data were analyzed using variance and regression. For qualitative factors, the means were compared using Tukey's test at 5%. For quantitative factors, regression models were selected based on the significance of the coefficients (t-test), the coefficient of determination (r²), and the biological consistency of the fit. The results showed that herbicides negatively affected the physiology of Enlist™ E3 soybeans. Significant reductions were observed in the photosynthetic rate, accumulation of soluble sugars, and concentration of photosynthetic pigments, in addition to an increase in phytotoxicity symptoms. However, foliar magnesium supplementation proved to be highly effective in mitigating these adverse effects. Foliar fertilization increased magnesium levels in leaf tissues, promoting greater integrity of photosynthetic pigments and favoring the maintenance of photosynthetic activity. An increase in stomatal conductance and sugar concentration was also observed. These benefits were directly reflected in productivity. Foliar application of magnesium reduced physiological stress symptoms, increased foliar nutrient levels, increased photosynthetic efficiency, sugar accumulation, and soybean productivity, especially in areas without weed competition. It was concluded that foliar supplementation with Mg is a viable and effective practice to mitigate the effects of herbicides and promote crop productivity.