Adsorption and Desorption of Atrazine Retention by Sugarcane Residue and Soils.

In this study, atrazine adsorption-desorption characteristics were quantified for sugarcane (Saccharum Spp. Hyb.) residue grown on Sharkey clay and Commerce loam soils. The residue, which covers the soil surface following combine harvesting, was sampled over several growing seasons from 2001 through 2009. Batch methods were used to quantify adsorption and desorption for a wide range of atrazine concentrations and reaction times. Desorption was carried out using successive dilutions.  Atrazine retention by the residue exhibited linear adsorption where the partitioning coefficient (K_d) increased over time of retention.  Adsorption-desorption exhibited strong hysteresis indicative of time-dependent retention and slow release by the residue. Limited atrazine sorption kinetics was observed by the two soils and their K_d values were an order of magnitude lower than that for the residue.  A multireaction model which accounts for kinetic and equilibrium type retention of was successful in describing the time-dependent atrazine adsorption and desorption behavior by the sugarcane residue over a wide range of applied concentrations. Atrazine was strongly sorbed by the residue where some 40% of the amount adsorbed was non-extractable by methanol.  Moreover, retention results indicated that a decreasing or increasing trends of atrazine retention by the sugarcane residue with time of decay was not observed. The use of an average retention (K_d) value to represent atrazine retention over an entire growing season is recommend.