Leaching, Phytotoxicity, and Weed Control of New Formulations of Alachlor

The use of commercially available formulations of alachlor has resulted in a serious environmental problem due to its leaching and migration to water sources. The objective of this study was to develop organo−clay based formulations that can significantly reduce leaching and improve weed control efficacy. We adsorbed the herbicide to montmorillonite clay particles whose surfaces were modified from hydrophilic to hydrophobic by preadsorbing to the clay an organic cation, such as benzyltrimethylammonium (BTMA) to reduce release of the herbicide into the soil. Alachlor adsorption was determined by gas chromatography. Organo−clay complexes of 0.5 mmol BTMA/g of clay gave larger adsorbed amounts and better formulations of alachlor as compared to BTMA preadsorbed up to the cation exchange capacity (0.8 mmol/g), whereas formulations without organic cations were not effective and gave little adsorption of the herbicide. The use of Fourier transform infrared spectroscopy showed that the optimal formulation also yielded the largest shifts of the stretching vibrations of the phenyl ring. The organo−clay formulations yielded slow release of the herbicide to the environment, maintaining the herbicidal activity in the top soil as measured by a bioassay using green foxtail and wheat as test plants. Laboratory and field experiments showed improved weed control at significantly reduced applied rate when alachlor was applied as organo−clay formulations. Keywords: Alachlor; montmorillonite; benzyltrimethylammonium; benzyltriethylammonium; benzyltributylammonium; hexadecylammonium; leaching; phytotoxicity; herbicidal activity