Shifts in Soil Microbial Communities During the Decomposition of Glyphosate Treated Soybean Residue.

Glyphosate (N-phosphonomethyl glycine) tolerant crops (GTC) have been introduced in the USA as an effective and low cost weed-management tool. There is concern that long-term use of glyphophsate affects soil microbial communities and potentially could negatively impact crops. Previous reports indicated that applications of glyophosate has had mixed effects on soil microorganisms but there is virtually no information on the effect of incorporating into soil GTC residue that has been treated with glyphosate. The objective was to study decomposition and the shift in the microbial structure when ¹³C labeled GTC and non-GTC soybean residues were amended to soils. Samples were incubated at 22^°C and 2/3 field capacity for 30 days. Samples were taken destructively at day 3, 7, 14, 21 and 30 and soil microbial community profile determined using phospholipid fatty acid (PLFA) analysis. Stable isotope analysis was also done to further explore the degree of incorporation of labeled glyphosate in the soil microbial biomass.  The information from our research will be helpful in understanding the effect of glyphosate on soil microflora.