Influence of pH and solution composition on the sorption of glyphosate and prochloraz to a sandy loam soil

Standard protocols for batch sorption experiments prescribe the use of 0.01 M CaCl 2 as the aqueous solution, but sorption can strongly depend on the solution composition. The present work quantifies the variation in sorption behavior of the herbicide glyphosate and the fungicide prochloraz to a sandy loam soil, arising from differences in pH, ionic strength, ortho-phosphate concentration, and dominant cation in solution (Ca 2+, K +, NH 4+). Using batch experiments, we measured the amount sorbed to the bulk fraction and clay-sized particles. From the adsorption and desorption isotherms, we estimated the Freundlich parameters, K ƒ and N . Sorption isotherms were mostly non-linear and manifested adsorption-desorption non-singularity. Adsorption K ƒ values were in the range 0.6–78.5 L kg −1 for glyphosate and 31.2–155 for prochloraz. The pH and ortho-phosphate affected the sorption of both glyphosate and prochloraz, whereas ionic strength and dominant cation only affected sorption of glyphosate.