Effect of glyphosate and glufosinate on nutritional content and agronomic performance of maize possessing cp4epsps and pat transgenes

The aim of this study was to check the tolerance level of maize possessing the transgenes cp4epsps and pat, exposed to high rates of glyphosate or glufosinate. Field experiments were carried out in 2016/17 at the first growing season; and the other in the second growing season, in Palotina, state of Paraná (PR), Brazil. The design was completely randomized block with 4 replications, which were set up with variations of rates of herbicides: glyphosate (0; 2,160; 4,320; 6,480 and 8,640 g ae ha-1) (experiment 1) and glufosinate (0; 1,500; 3,000; 4,500 and 6,000 g ai ha-1) (experiment 2). The application was performed at the V4 stage. Plants were evaluated for injuries, final plant height, stem diameter, 100-grain mass, yield and content of P, K, S, Fe, Cu and Zn. The results show that there was no reduction in yield and 100-grain mass, as well as changes in nutrient contents, even with the use of high rates of glyphosate and glufosinate. This is explained by the rapid recovery of maize hybrids under favorable developmental conditions. Despite causing injuries and decreased height, application of glyphosate (up to 8,640 g ae ha-1) or glufosinate (up to 6,000 ai ha-1) did neither reduce yield and 100-grain mass nor the nutrient contents of grains. This shows the high selectivity of these herbicides. Nonetheless, crop injury and reduction in height were observed in maize plants for herbicide application. This indicates the risks of using herbicides above the rates recommended in the package insert, despite the absence of deleterious effects on yield