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 wee k. Soil concentrations of 0.2-0.8 mg/kg were maintained for at least a n additional 8 weeks. A large portion (35-70%) of the active ingredien t was still present in the CRFs at the conclusion of the experiment. A pplication of alachlor as the commercial formulation resulted in 50% d issipation after only 3-4 days. Alachlor released from CRFs with a sma ller diameter resulted in higher soil concentrations (1.2 mg/kg) after 18 days. In column leaching studies the leaching of alachlor, atrazin e, and trifluralin from CRFs was considerably reduced with respect to leaching of the same compounds from commercial formulations. The relea se of alachlor from an Al-pillared clay CRF and its subsequent transpo rt in soil columns showed that pillared clays can be used for controll ed release of herbicides, but more work is necessary before the effect s of the many factors involved in the release of the active ingredient s from pillared clays are completely understood.