Use of modified montmorillonites to reduce herbicide leaching in sports turf surfaces: Laboratory and field experiments

The risk of ground water contamination resulting from rapid leaching of highly mobile pesticides can be reduced through the application of the pesticide adsorbed on a suitable carrier, which limits the amount of pesticide readily available for undesirable leaching losses. The herbicide simazine was used as a model of highly mobile herbicide applied in sports turf surfaces. We investigated the ability of selectively modified montmorillonites to retard the release of the herbicide into the aqueous soil solution and to reduce herbicide leaching from the soil. Fe3+-Wyoming montmorillonite (Fe-SW), hexadecyl trimethylammonium-Arizona montmorillonite (HDTMA-SA) and octadecylammonium-Arizona montmorillonite (ODA-SA) were mixed with simazine following two different protocols. The resulting complexes were assayed as slow release formulations of the herbicide. In the laboratory, batch release and column leaching tests showed that all montmorillonite-based formulations of simazine released the herbicide slowly in aqueous solution, which resulted in reduced simazine leaching through soil columns compared to the application of the free herbicide. Pretreatment of the soil surface layer with Fe-SW was also effective in retarding the leaching of free simazine through the soil column compared to its leaching in untreated soil columns. In a field experiment, a Fe-SW-based formulation of simazine was applied to 1 m2 field plots, previously seeded with Princess 77 bermudagrass to simulate a typical sports turfgrass surface. The field experiment revealed that the montmorillonite-based formulation of simazine displayed similar herbicidal efficacy and slower vertical movement of the herbicide compared to a standard commercial formulation. This study shows the usefulness of montmorillonite to reduce ground water contamination by intensive herbicide application in high-risk scenarios such as sports turfgrass surfaces.