IMPACT OF TILLAGE PRACTICE ON RUNOFF AND PESTICIDE TRANSPORT

A two-year study was conducted to evaluate the effect of no-till (NT) and conventional-till (CT) corn production practices on pesticide loss in runoff from natural rainfall. Runoff from two NT and two CT plots [0.25 to 0.5 ha (.62 to 1.2 ac)] was measured and runoff water samples were analyzed for atrazine, cyanazine and alachlor. Runoff (of water) was greater from NT than from CT plots when the time between rainfall events was less than seven days, but runoff from CT was greater-than- or-equal-to NT when seven or more days passed between rains. The conce ntrations of atrazine and cyanazine were two to 10 times higher in run off from NT than from CT; concentrations of alachlor, the only microen capsulated herbicide that was applied, were unaffected by tillage. Con centrations of all pesticides were highest for the first runoff event after application and then decreased rapidly with each subsequent runo ff. The time between application and the first runoff event was three and eight days for 1990 and 1991, respectively, which resulted in five to 10 times higher concentrations of all pesticides in the first even t for 1990 than 1991. Total loss (percent of applied) of atrazine, cya nazine and alachlor was 1.5, 1.6, and 0.3 (NT) and 1.0, 0.7, and 0.5 ( CT), respectively, for 990; corresponding losses for 1991 were 0.8, 0. 6 and 0.2 (AT) and 0.3, 0.2 and 0.2 (CT).