Exchangeable and microbial potassium
Exchangeable K increased with glyphosate treatment. This result could be expected, since the glyphosate formulation contains K salt. Each field application rate of glyphosate included 11 μg K g−1 dry soil (2× = 23 μg K g−1). Therefore, after six applications of glyphosate, the 1× and 2× glyphosate treatments received a total of 66 and 138 μg K g−1, respectively. Increases in exchangeable K reflect these additions, with each soil showing an increase of approximately 100 μg K g−1 after six months at the 2× glyphosate treatment level (Fig. 5). These results indicate that K added to the soil with glyphosate is not readily converted to microbial biomass K, nor fixed between clay layers as nonexchangeable K. The majority of K added stayed in the plant available and exchangeable form.