ATRAZINE, ALACHLOR, AND METOLACHLOR MOBILITY THROUGH 2 SANDY WISCONSIN SOILS

Pesticide mobility through Sparta sand from the Lower Wisconsin River Valley (LWRV) and Plainfield sand from the Central Sands (CS) of Wisco nsin was examined to interpret results from state-sponsored groundwate r monitoring programs and to identify fundamental mechanisms important in pesticide transport through the unsaturated zone. The mobility of C-14-labeled atrazine oro-(4-ethylamino)-6-(isopropylamino)-s-triazine ], alachlor [2-chloro-N-(2,6-diethyl-phenyl)-N-(methoxym ethyl) acetam idel, and metolachlor -ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethy l) acetamide] was monitored through replicated intact soil column-micr olysimeters. Soil columns of Sparta sand (sandy, mixed, mesic Entic Ha pludolls) from the LWRV and Plainfield sand (sandy, mixed, mesic Typic Udip-samments) from the CS were instrumented in the greenhouse to sim ulate field conditions. All pesticides were shown to be much more mobi le through the Sparta sand as compared to Plainrield sand. Peak atrazi ne concentration was 15 times greater in the leachate from the Sparta soil than from the Plainrield sand. Percentage loss of applied pestici de was four times greater in the leachate from the Sparta soil than fr om the Plainfield sand. Similar results were found for metolachlor and alachlor. The relative order of mobility for each soil was found to b e atrazine > metolachlor > alachlor. Factors found to contribute to in creased mobility of pesticides through the Sparta sand include higher hydraulic conductivity, smaller water-holding capacity, and less atraz ine adsorption due to less organic C and clay content. The hydraulic c onductivity (K(sat)) of the upper rootzone (0-20 cm) of the Sparta soi l is rive times faster than the Plainfield soil. The water-holding cap acity and the atrazine adsorption coefficient (K(d)) of the Plainfield sand were measured to be 1.6 and 1.8 times greater, respectively, tha n those of the Sparta soil.