The feasibility of using starch-encapsulated atrazine to minimize convective transport under conditions favoring preferential flow was evaluated. Forty small, undisturbed, soil columns (45 cm2 x 3 cm) were removed from an established no-tillage management site and randomly grouped into one of five atrazine treatments: 1) technical grade; 2) borate process, starch-encapsulated; 3) jet-cooked, pearl starch-encapsulated; 4) jet-cooked, waxy starch-encapsulated; and 5) untreated control. Columns were drip-irrigated at the rate of 2.5 cm every three days. Highest atrazine levels, 1,30 mg L-^ were observed in the effluent from columns receiving technical-grade atrazine after the first irrigation (2.3 pore volumes), even though piston flow theory indicated that atrazine should not have appeared before 21.9 pore volumes. Computer simulations using the general convection-dispersion equation with first-order dissipation and linear adsorption also significantly underpredicted atrazine mobility. All encapsulated formulations, relative to technical-grade, revealed significantly lower initial atrazine levels in the effluent. Cumulative effluent concentrations indicate that after 16.1 pore volumes, 35,10,3, and <1% of the available atrazine had been leached fi-om the technical-grade, borate, pearl, and waxy starch formulations, respectively.
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Gish et al. (1991) studied this question.