Reducing the transport of herbicides and herbicide metabolites from agricultural application zones with vegetated filter strips

There are conflicting reports in the literature concerning vegetated filter strips (VFS) and the contribution of a sorption mechanism to herbicide trapping efficiency (TE). Moreover, adsorption, desorption, and mineralization of herbicide metabolites in vegetated filter strip soil (VFSS) have not been evaluated. Yet, these data are needed to predict the transport of these compounds through VFSS. To address the contribution of herbicide mass adsorbed (M _as) to TE, simulated runon experiments were conducted to compare TE and M_as among metolachlor, metolachlor oxanilic acid (OA), and metolachlor ethanesulfonic acid (ESA) in buffalograss filter strips. Subsequently, the potential transport of these compounds was assessed in laboratory experiments where adsorption, desorption, and mineralization parameters were compared between a cultivated Houston Black clay (CS) and an adjacent VFS established in a mixed stand of bermudagrass and buffalograss. Parallel field and laboratory experiments were conducted with atrazine, desethylatrazine (DEA), deisopropylatrazine (DIA), diaminoatrazine (DA), and hydroxyatrazine (HA).;In the field experiment, TE was greater for metolachlor (25.3%) compared to OA (15.5%) and ESA (14.2%). Significantly more metolachlor (17.3%) was retained as M_as compared to either metabolite (≤7.0%). An identical trend was observed in the atrazine study. These data demonstrate that sorption to the VFS sorbents (grass, grass thatch, and/or soil surface) is an important retention mechanism. Retention differences among compounds were attributed to hydrophobic interactions among the compounds and the VFS sorbents.;In the laboratory experiments, organic carbon content, microbial activity, microbial numbers, and soil enzymatic activity were higher in the VFSS compared to the adjacent CS. Sorption and mineralization data for metolachlor, ESA, and OA indicate that the transport of these compounds is reduced in the VFSS. In contrast, our sorption and mineralization data for atrazine, DEA, and HA demonstrate that the transport of these compounds may not be reduced in the VFSS. However, the potential transport of DIA is lower in the VFSS.