Glyphosate adsorption in continental and Mediterranean vineyard soils of Croatia

Soil portfolio is one of the ultimate viticultural considerations when planting grape vines. However, soil composition is also a crucial determining factor for agrochemical transfer to fresh/groundwater resources as a result of chemical-soil particle interactions. Adsorption coefficients are known to be the most sensitive parameters used for water pollution risk assessment. Therefore, adsorption interactions should be studied in as many soil composition as possible scenarios and the adsorption data should be considered with certain physical and chemical pedovariables in order to predict the mobility of agrochemicals down the soil profiles. Glyphosate is one of the most frequently used herbicides in a wide range of cropping, notably in vineyards, for broad- spectrum control of weeds. This study presents the glyphosate adsorption parameters and their variation considering the soil composition in different agroecological conditions. The batch- sorption experiments were performed in two different vitisols of the continental (texture- heavier) and Mediterranean (texture-lighter) part of Croatia. Soil samples from both vineyard locations were collected at four depths from 0 to 100 cm and characterized on certain chemical/physical variables. Soil composition differed between the studied soil layers. Glyphosate was extracted from aqueous phase of soil suspensions by solid-phase extraction procedure using a weak anion exchange sorbent. Derivatization was performed prior to GC-MS analysis with a mixture containing trifluoroacetic anhydride and trifluoroethanol. The analytical results were well fitted to the Freundlich sorption isotherm. Glyphosate adsorption in soils from both origins corresponded to the L-type of isotherm, while glyphosate adsorption intensity was generally higher in heavier silty-clayic vs. lighter sandy- silty soil profiles. The glyphosate adsorption intensity was correlated with selected soil properties (pH, organic matter content, particle size distribution, conductivity, P/K content) and the glyphosate mobility through soil profile was considered.