The effect of glyphosate and glyphosate-resistant maize and soyabeans on soil micro-organisms and the incedence of disease
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During the present study it was found that herbicides, applied at the recommended dosage, has an inhibitory effect on fungi in vitro. However, when the effect of herbicides on soil microbial and bacteria activity was tested in experimental microcosms, it was found that soil with a high organic matter content had a buffer effect on soil microbes. Microbial activity increased after glyphosate treatment in rich soil microcosms, indicating tha soil microbes utilized glyphosate as a source of carbon and nutrients or that the toxicity of glyphosate to specific soil microflora and microfauna increased the available nutrient base for increased activity of resistant organisms. No significant differences were observed in terms of rhizosphere bacterial activity between glyphosate resistant (GR) maize and soybean in comparison to their conventional counterparts. Clay- and organic matter concentration in soil did however have a significant influence. Soil with a high clay- and organic matter content had higher microbial activity than soil with low clay- and organic matter content. Higher ergosterol levels were also isolated from high clay- and organic matter soil than low clay- and organic matter soil. Dry root biomass of GR maize and soybean kultivars did not differ significantly from their conventional counterparts. However, when glyphosate was applied to GR maize and soybean, dry root biomass decreased significantly compared to GR maize and soybean which received no glyphosate treatment. The same pattern was observed in terms of ergosterol concentrations, thus indicating that glyphosate had a physiological effect on the respective crop roots.