Conclusions
The addition of glyphosate stimulates microbial respiration in soil that had a previous history of glyphosate applications. Repeated applications of glyphosate to a soil that had never received glyphosate under field condition had an initial stimulation of respiration but subsequently declined to nearly zero and was lower than its control. This indicates that it was not well adapted to degrade glyphosate. The three soils that were used which varied from zero, medium to high long-term application rates of glyphosate were the same soil type and had similar properties. Therefore, this apparent shift in the microbial community was not detected by EL-FAME analysis. It seems obvious that analysis of communities must be done by methods that are more sensitive in identifying shifts at a higher resolution, such as nucleic acid analyses. The results indicate that K added to the soil with glyphosate was not readily converted to microbial biomass K, nor fixed between clay layers as nonexchangeable K. The majority of K added remained in the plant available and exchangeable form. Thus, from this we do not find evidence that glyphosate is decreasing plant available K indexes.