Glyphosate and AMPA adsorption in soils: laboratory experiments and pedotransfer rules
2016
Adsorption of the herbicide glyphosate and its main metabolite AMPA (aminomethylphosphonic acid) was investigated on 17 different agricultural soils. Batch equilibration adsorption data are shown by Freundlich adsorption isotherms. Glyphosate adsorption is clearly affected by equilibration concentrations, but the nonlinear AMPA adsorption isotherms indicate saturation of the adsorption sites with increasing equilibrium concentrations. pHCₐCₗ₂ (i.e. experimental pH) is the major parameter governing glyphosate and AMPA adsorption in soils. However, considering pHCₐCₗ₂ values, available phosphate amount, and amorphous iron and aluminium oxide contents by using a nonlinear multiple regression equation, obtains the most accurate and powerful pedotransfer rule for predicting the adsorption constants for these two molecules. As amorphous iron and aluminium oxide contents in soil are not systematically determined, we also propose a pedotransfer rule with two variables—pHCₐCₗ₂ values and available phosphate amount—that remains acceptable for both molecules. Moreover, the use of the commonly measured pHwₐₜₑᵣ or pHKCₗ values gives less accurate results compared to pHCₐCₗ₂ measurements. To our knowledge, this study is the first AMPA adsorption characterization for a significant number of temperate climate soils.
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