Glyphosate resistant soybean growth and yield affected by glyphosate and phosphate fertilization

Abstract

Glyphosate is the most used herbicide worldwide and glyphosate-tolerant soybean planted in almost all cultivated areas. In Brazil, the area cultivated with transgenic soybean reaches more than 90%. Recently, the application of glyphosate in tolerant soybean has assumed the possibility to injury the crop under certain conditions and herbicides formulations. Phosphate fertilization can directly influence glyphosate uptake in plants because glyphosate translocation inside cells is related with phosphate transporters. Therefore, a study was conducted in two steps intended to determine if different doses of phosphate fertilization and/or glyphosate mode of spraying could modify glyphosate susceptibility of glyphosate-tolerant soybean, affecting crop development and yield. We tested two glyphosate doses and its interaction with mode of spraying and different glyphosate doses interaction with phosphate soil-fertilization. Experiment I was set up in a two by two factorial design, testing two doses of isopropylamine salt glyphosate (960 and 1,440 g ae ha-1) and two modes of glyphosate application (single spraying and sequential spraying). Experiment II was set up in a two by three factorial design, testing two doses of glyphosate (960 and 1,440 g ae ha-1) and three doses of phosphate fertilization (54, 108 and 162 kg ha-1 of P2O5). In both experiments, weed community was evaluated based on number of individuals and their respective dry mass accumulation. Crop was evaluated in dry mass of leaves, dry mass of stem, dry mass of pods, dry mass of shoot, plant height and grain yield. The use of glyphosate in a sequential spraying (960 + 480 g ae ha-1) or in higher dose (1,440 g ae ha-1) provides a highly efficient weed control and a high-performance crop growth and yield. The additional soil-fertilization with phosphate in this case does not affect soybean since no crop injury was observed.