Abstract: Quantifying herbicide retention in the soil environment is essential for minimizing their runoff and contamination of groundwater resources. In this study, atrazine retention characteristics were carried out for sugarcane (Saccharum spp. Hyb.) residue grown on Sharkey clay and Commerce loam soils. The residue that covers the soil surface following combine harvesting was sampled over several growing seasons. 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 (Kd) 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 by the two soils was observed, and their Kd values were an order of magnitude lower than that for the residue. A multireaction model that accounts for kinetic- and equilibrium-type retention 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 nonextractable by methanol. Moreover, retention results indicated that a decreasing or increasing trend of atrazine retention by the sugarcane residue with time of decay was not observed. The use of an average retention (Kd) value to represent atrazine retention over an entire growing season is recommended.
School of Plant, Environmental and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, Louisiana, USA.
Address for correspondence: Prof. H. Magdi Selim, School of Plant, Environmental and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: This study was funded in part by the Nonpoint Source Program of the Louisiana Department of Environmental Quality (section 319).
Received December 4, 2011.
Accepted for publication January 4, 2012.