Seletividade de sais de Glyphosate aplicados em isolado ou associados com Chlorimum-ethyl em diferentes horários na cultura da soja

Abstract

Currently, there is a scarcity of research evaluating the efficiency of glyphosate salts (ammonium, isopropylamine, and potassium) and their effects on soybeans when applied at different times, either alone or in combination with other herbicides. Therefore, this study aimed to assess the selectivity of glyphosate salt formulations applied alone or in combination with chlorimuron-ethyl at different times, focusing on physiological characteristics and grain yield components of soybeans. The experimental design used in the study was a randomized block design arranged in a factorial scheme (4x2+1) with four replications. Factor A comprised the herbicides (chlorimuron-ethyl, glyphosate isopropylamine salt, glyphosate ammonium salt, glyphosate potassium salt, and mixtures of these products), while Factor B included the application times (6:30 AM and 12:30 PM). Additionally, a weed-free control was included alongside the herbicide treatments. Phytotoxicity evaluations on soybeans were conducted at 7, 14, 21, 28, 35, and 42 days after treatment (DAT). At 28 DAT, the physiological characteristics of the soybeans were evaluated, including internal carbon concentration, photosynthetic rate, stomatal conductance, transpiration rate, water-use efficiency, carboxylation efficiency, and chlorophyll index. At harvest, the grain yield components were measured: number of pods per plant, number of grains per plant, weight of 1,000 grains, and grain yield. The isolated application of chlorimuron-ethyl caused the highest phytotoxicity to the soybean cultivar DM 57i52. The use of glyphosate isopropylamine salt, ammonium salt, and potassium salt showed lower phytotoxicity to soybeans. Tank mixing chlorimuron-ethyl with glyphosate salts increased soybean phytotoxicity. The weed-free control, glyphosate ammonium salt, and its combination with chlorimuron-ethyl demonstrated better performance in terms of transpiration rate, stomatal conductance, photosynthetic rate, and carboxylation efficiency in soybeans. Overall, the weed-free control and glyphosate ammonium salt showed the best results for grain yield components. Herbicide application at 6:30 AM did not affect soybean grain yield, while the use of glyphosate ammonium salt, either alone or in combination with chlorimuron-ethyl at 12:30 PM, had a negative effect on this variable. In general, herbicide application at 6:30 AM was less harmful to soybeans than application at 12:30 PM.