Effects of glyphosate and foliar fertilizers on the glyphosate resistant (GR) soybean

Abstract

Currently the soybean crop is responsible for a great share of the protein consumed by humans and animals, it is also a source of oil and renewable materials for the industry. Due to the importance of soybeans worldwide, especially genetically modified soybeans (resistant to glyphosate - GR), the improvement in yield indexes became the targets of promising research. The objective of this work was to evaluate the responses of the "GR" soybean crop as a function of glyphosate herbicide and foliar fertilizer, under soil without nutrient deficiency. The experiment was conducted in a randomized block design with four replications, consisted of two factors. Factor A was consisted by glyphosate (1080 and 2160 g a.e ha-1) and factor B by foliar fertilizers (Fertilizer A - Mg= 5%, Mn= 0,5%, Mo= 0.5%, L-Glutamic acid= 5% and glycine betaine 3%; Fertilizer B - Zn (5%), Mn (3%), Cu (0,5%), B (0.5%) and S (4%); Fertilizer C - Mo and L-Glutamic acid). The treatments were applied isolated and in mixtures, plus the control treatment, totalizing 21 treatments. The variables evaluated were phytotoxicity at 14 and 21 DAT, a thousand-grain weight and grain yield. The analysis of variance was performed and, when significant, the comparison of groups of treatments using orthogonal contrasts was applied to all variables. Soybean yield was also compared to the means of the treatments by the Scott-Knott test (p≤0.05). Phytotoxicity was detected in the soybean crop at 14 DAT with the application of glyphosate, foliar fertilizers and the association of the two products. However, only the highest dose of glyphosate, with or without foliar fertilizers, generally reduced crop grain yield. In addition, the application of foliar fertilizers isolated and associated with glyphosate, in soils with adequate levels of nutrients, does not increase thousand-grain weight or grain. It is concluded that the glyphosate dose for soybeans should be respected and foliar fertilizers should be carefully studied before recommendation.