ISSN: 1579‐4377 ADSORPTION BEHAVIOR OF GLYPHOSATE IN SOME CITRUS GARDEN SOILS OF IRAN * Rafiei Keshteli, M. * , Farahbakhsh, M., Savaghebi, G.R. Department of Soil Science, Faculty of Agricultural Engineering & Technology, College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran. Mamatir.majid@gmail.com ABSTRACT Glyphosate is a herbicide used in large quantities and, as a consequence, is a common contaminant in groundwater and surface water. The sorption of herbicides by soil is a very important process and their degradation in aqueous environments is highly dependent upon its adsorption on soil surfaces. This investigation was performed to study adsorption of glyphosate in six citrus garden soils of north of Iran. The soil samples were thoroughly characterized for their physical and chemical properties, particularly organic matter and iron and aluminum oxides. Both Langmuir and Freundlich isotherms represented the adsorption data well in all cases although Langmuir equation showed a better estimate of glayphosate adsorption. Amounts of Freundlich adsorption coefficient (K f ) are in the range of 42.52- 77.46 LKg -1 and Langmuir absorption coefficient (K L ) in the range of 0.326-1.089 LKg -1 . Maximum absorption coefficient in the soils studied was the soil that had the highest organic carbon content. K f and K L had shown significant correlations with soil organic carbon. KEYWORDS Herbicide, Glyphosate, Adsorption isotherm, Langmuir equation, Organic matter.