Organo-clay formulation of acetochlor for reduced movement in soil

This study aimed to design ecologically acceptable formulations of acetochl or by adsorbing it on montmorillonite exchanged by a small organic cation, phenyltrimethylammonium (PTMA). Adsorption of acetochlor on the clay minera l exchanged with different organic cations and its release from these compl exes were determined by GC and modeled by Langmuir equation. Interactions b etween acetochlor molecules and the exchanged organic cation on the clay su rface were studied by Fourier transform infrared spectroscopy. Leaching of acetochlor in soil was determined by a bioassay using a column technique an d Setaria viridis as a test plant. The adsorbed amounts of acetochlor on mo ntmorillonite exchanged by PTMA at a loading of 0.5 mmol/g of day were high er than at a loading up to the cation-exchange capacity, i.e., 0.8 mmol/g, and were higher than obtained by using a clay mineral exchanged by other or ganic cations. Preloading montmorillonite by PTMA at 0.5 mmol/g yielded max imal shifts of the infrared peaks of the herbicide. The above formulation o f acetochlor yielded slow release in water and showed improved weed control in field and greenhouse experiments in comparison with the commercial form ulation. The PTMA-clay formulation of acetochlor maintained herbicidal acti vity in the topsoil and yielded the most significant reduction in herbicide leaching and persistence under field conditions. The application of this f ormulation can minimize the risk to groundwater and can reduce the applied rates.