Controlled Release of Pesticides into Soils from Clay−Polymer Formulations

Alachlor was released from a controlled-release formulation (CRF) when applied to a sandy loam soil under conditions of constant temperature and moisture and achieved concentrations of 0.1−0.2 mg/kg after 1 week. Soil concentrations of 0.2−0.8 mg/kg were maintained for at least an additional 8 weeks. A large portion (35−70%) of the active ingredient was still present in the CRFs at the conclusion of the experiment. Application of alachlor as the commercial formulation resulted in 50% dissipation after only 3−4 days. Alachlor released from CRFs with a smaller diameter resulted in higher soil concentrations (1.2 mg/kg) after 18 days. In column leaching studies the leaching of alachlor, atrazine, and trifluralin from CRFs was considerably reduced with respect to leaching of the same compounds from commercial formulations. The release of alachlor from an Al-pillared clay CRF and its subsequent transport in soil columns showed that pillared clays can be used for controlled release of herbicides, but more work is necessary before the effects of the many factors involved in the release of the active ingredients from pillared clays are completely understood.