Glyphosate Influence on the Soil Microorganism Sensibility, Physiological Parameters of the Plant, Isoflavones and Residues in the Seeds and Soil

The use of Glyphosate herbicide is the best way to control weed growing when cultivating genetically modified soybean [Glycine max (L.) Merr.] resistant to glyphosate (N-phosphono-methyl-glycine) (GR). However, there have been doubts about the safety of this herbicide use concerning its effects on the plant, quality of grains and on the soil cultivated. Hence, the present study aimed at evaluating the effects of weed management two soybean cultivars (GR) and its conventional isogenic genotype with the use of different doses of glyphosate on soil processes and microorganisms, physiology and metabolism of the plant along with possible contamination of soil and seed by herbicide residues. For this purpose, two soybean genotypes, one GR BRS 243 RR and a conventional (isogenic genotype) were grown under different weed control methods: hand weeding and glyphosate herbicide application. The study was performed in Rio Grande do Sul State, during the crop seasons of 2008 to 2009, 2009 to 2010, 2010 to 2011 and 2011 to 2012, with evaluations of soil microbial biomass and respiration, chlorophyll, nitrogen, ureides, nitrates, carotenoid, isoflavone content in seeds, and glyphosate and aminomethylphosphonic acid (AMPA) residues in seeds and soil. The use of glyphosate positively affected the microbial biomass, basal respiration and seeds yield. On the other hand, the chlorophyll, nitrogen, ureides, nitrates, carotenoid, and isoflavone contents in seeds were unaffected by the treatment. Even though we used the recommended application doses, the glyphosate residues in the seeds were above the levels permitted by the Brazilian law. Also, AMPA residues were detected in the soil and the seeds.