Retention of Metribuzin by Sugarcane Residue

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Assessment of herbicide retention in the soil environment is essential for minimizing their potential contamination of surface and groundwater resources. In this study, metribuzin retention characteristics by sugarcane mulch residue were quantified. Batch methods were used to quantify adsorption and desorption of metribuzin by the residue over a wide range of input concentrations and reaction times. Desorption was carried out after 1- and 21-day adsorption, which was followed by methanol extraction. Metribuzin retention by the residue exhibited linear adsorption where the partitioning coefficient (Kd) increased over time. Adsorption-desorption exhibited strong hysteresis indicative of time-dependent retention. The extent of hysteresis and nonextractable or residual amounts increased as the time for adsorption increased. A multireaction model provided good description of the time-dependent adsorption and desorption behavior for all input concentrations. In addition, based on measured Kd values, we found that metribuzin retention by the residue did not change significantly with the age of the decaying residue. Metribuzin breakthrough results (breakthrough curves) from miscible displacement experiments showed high mobility of metribuzin in residue-amended Sharkey and Commerce soil columns. Metribuzin breakthrough curves exhibited gradual release during leaching as well as significant responses to flow interruption and were well described using the multireaction model.