Release of Atrazine and Alachlor from Clay-Oxamide Controlled-ReleaseFormulations¤

Controlled-release herbicide formulations have been shown to decrease the leaching potential of several herbicides under laboratory and Ðeld conditions. The utility and efficacy of these formulations may be improved by combining several herbicides and a fertilizer source in a single formulation. The objective of these studies was to develop granular alginate formulations that were composed of a combination of the herbicides atrazine and alachlor with the slow-release nitrogen source oxamide (ethanediamide). Controlled release of the herbicides was obtained by addition of selected minerals, including calcium bentonite, Ðnegrind bentonite, montmorillonite K10, kaolinite and iron (III) oxide. A formulation without clay was used as a comparison. The formulations tested had herbicide active ingredient contents ranging from D0É02 to 0É54% and a nitrogen content of 21%. Release of the herbicides was studied by equilibrating the formulations with deionized water on a rotary shaker at 200 rev min~1 and sampling at regular time intervals up to 104 hours. The minerals used in the di†erent formulations inÑuenced the herbicide active ingredient composition, as well as the release properties of the individual formulations. The atrazine content of the formulations decreased in the order calcium bentonite[ Ðne-grind bentonite [ kaolinite[ montmorillonite \ iron oxide [ no clay. For alachlor the content decreased in the order of calcium bentonite[ Ðne-grind bentonite [ montmorillonite [ iron oxide[ kaolinite[ no clay. Controlled release of atrazine (i.e. reduction in release rate) varied in the order calcium bentonite [ iron oxide[ montmorillonite [ Ðne-grind bentonite \ kaolinite[ no clay, and for alachlor Ðne-grind bentonite[ calcium bentonite [ montmorillonite [ no clay\ kaolinite\ iron oxide. A certain percentage of the applied active ingredient of both alachlor and atrazine was not recovered. From 5 to 27% of the active ingredient was not released, with the greatest retention by the bentonite formulations. Release of nitrogen was not strongly inÑuenced by mineral type, although a trend indicated greater release with formulations containing kaolinite. 1998 SCI ( Pestic. Sci., 53, 233È240 (1998)