Glyphosate impact on C and N microbial functional groups in soybean rhizosphere

Abstract

The no-tillage system requires a higher use of herbicides to control weeds before sowing, increasing the concern over the effect that such products might have on the environment. However, few studies reporting the influence of glyphosate on soil microorganisms are available in the literature. The aim of this work was to evaluate the effect of two formulations of glyphosate on functional groups of microorganisms in soybean rhizosphere. The experiment was performed in a greenhouse, and the treatments were the isopropylamine salt and the ammonium salt of glyphosate at the maximum and twice the maximum allowed dose. The control treatment had no application. The populations of soil bacteria, fungi, actinomycetes, fluorescent pseudomonas, cellulolytics, amylolytics, proteolytics and free-living N-fixing were determined by plate counts on selective media. Plant root dry weight, shoot dry weight and the number and dry weight of nodules were determined. The application of herbicides had little effect on the populations of microorganisms, as well as on plant growth. Nevertheless, the interactions among some populations of microorganisms and between these and the plant were influenced by the formulation of the glyphosate applied.