PREDICTING PESTICIDE TRANSPORT IN MULCH AMENDED SOILS: A TWO-COMPARTMENT MODEL

Authors: Ma, Liwang; SELIM, H. - LOUISIANA STATE UNIVERSIT

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2004
Publication Date: 1/1/2005
Citation: Ma, L., Selim, H.M. 2005. Predicting pesticide transport in mulch amended soils: a two-compartment model. Soil Science Society of America Journal. 69:318-327. 2005.

Interpretive Summary: In this study we quantified the retention characteristics and mobility of herbicides in soils when sugarcane (Saccharum Spp. Hyb.) mulch residue was present. Specifically, adsorption and desorption kinetic batch experiments were carried out to quantify atrazine retention by the mulch residue over time. Atrazine sorption exhibited time-dependent behavior and was followed by slow release regardless of input concentration. A kinetic/equilibrium model based on a second-order two-site (SOTS) formulation was successful in describing atrazine adsorption versus time by the mulch residue. One set of model parameters was capable of describing atrazine release based on six successive desorption steps. As a test for the applicability of the model, data sets from two other experiments where sorption and release was measured for extended time periods (1348 and 2476 h), were successfully predicted by the SOTS model. Miscible displacement methods were used to measure the mobility of atrazine in packed columns where the mulch residue was mixed with a reference sand material or a Sharkey clay soil. For two reference sand columns, the SOTS model was capable of predicting atrazine transport provided that best-fit parameters were obtained through nonlinear optimization. Use of independent set of parameters from our batch experiments did not adequately describe atrazine mobility in the sand columns. In contrast, for a Sharkey soil column, a two-compartment SOTS model was successful in predicting atrazine breakthrough results where independently estimated parameters for the mulch residue and the soil matrix were used as the input parameters.

Technical Abstract: In this study we quantified the retention characteristics and mobility of herbicides in soils when sugarcane (Saccharum Spp. Hyb.) mulch residue was present. Specifically, adsorption and desorption kinetic batch experiments were carried out to quantify atrazine retention by the mulch residue over time. Atrazine sorption exhibited time-dependent behavior and was followed by slow release regardless of input concentration. A kinetic/equilibrium model based on a second-order two-site (SOTS) formulation was successful in describing atrazine adsorption versus time by the mulch residue. One set of model parameters was capable of describing atrazine release based on six successive desorption steps. As a test for the applicability of the model, data sets from two other experiments where sorption and release was measured for extended time periods (1348 and 2476 h), were successfully predicted by the SOTS model. Miscible displacement methods were used to measure the mobility of atrazine in packed columns where the mulch residue was mixed with a reference sand material or a Sharkey clay soil. For two reference sand columns, the SOTS model was capable of predicting atrazine transport provided that best-fit parameters were obtained through nonlinear optimization. Use of independent set of parameters from our batch experiments did not adequately describe atrazine mobility in the sand columns. In contrast, for a Sharkey soil column, a two-compartment SOTS model was successful in predicting atrazine breakthrough results where independently estimated parameters for the mulch residue and the soil matrix were used as the input parameters.