IRRIGATION AND POLYMER EFFECTS ON HERBICIDE TRANSPORT THROUGH THE UNSATURATED ZONE OF A SPARTA SAND

State-sponsored monitoring programs show that the Sparta sand (sandy, mixed, mesic Entic Hapludoll) of the Lower Wisconsin River Valley (LWR V) is susceptible to herbicide movement through the vadose zone, espec ially atrazine oro-(4-ethylamino)-6-(isopropylamino)-s-triazine]. Expe riments were initiated to examine the effect of irrigation scheduling and pesticide formulation on transport through the vadose zone. Intact Sparta sand (SP) columns were extracted from the LWRV and instrumente d to simulate temperature, irrigation and drainage conditions encounte red in the field. Labeled C-14-atrazine, alachlor [2-chloro-N-(2,6-die thylphenyl)-N-(methoxymethyl) acetamidel, and metolachlor 2-ethyl-6-me thylphenyl)-N-(2-methoxy-1-methylethyl ) acetamide] were monitored in the leachate. Treatments included irrigation schedules to match no-irr igation or rainfed (RF), evapotranspiration (ET) and ET plus an additi onal 25% (ET + ). Formulation treatments consisted of standard pestici de tank-mix mixtures with and without the addition of a polymer (2% by volume). Increased water input significantly increased metolachlor tr ansport through the SP profile. Due to variability in the leachate dat a, no significant differences in the total amount of atrazine leached through the columns were shown to exist between the ET and ET+ treatme nts; however, after initial irrigation, atrazine concentration in leac hate from ET + treatment was 10 to 15 times greater than leachate of t he ET treatment. When compared to the standard herbicide formulation, the use of the polymer significantly reduced and delayed the peak conc entrations of metolachlor in the leachate. A significant difference al so was observed in the amount of metolachlor retained in the surface s oil (0-10 cm) of those columns receiving the polymer treatment compare d to those receiving the standard application of the herbicide.