ASSESSMENT OF MANAGEMENT-PRACTICES FOR REDUCING PESTICIDE RUNOFF FROM SLOPING CROPLAND IN ILLINOIS

The influence of tillage system and contouring practice on runoff of soil-applied alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide], carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate), and terbufos (S-[(tert-butylthio)methyl] O,O-diethyl phosphorodithioate) from small plots (30 m2) were studied using a rainfall simulator. Plots were planted in corn (Zea mays L.) in 1983, soybean [Glycine max (L.) Merr.] in 1984, and corn in 1985. Runoff was measured during a 60-min event with a rainfall intensity of 63 mm/h. During 1984, moldboard-plowed and no-till systems were studied with rows oriented on the contour or up-and-down slope (7-11% slope). Compared to moldboard plow, up-and-down slope no-till and contouring significantly reduced runoff of carbofuran and alachlor. Percentage of applied carbofuran lost in runoff and sediment ranged from 1% (contoured moldboard) to 11% (up-and-down slope moldboard). Percentage of applied alachlor lost ranged from 1% (contoured no-till) to 2% (contoured moldboard). During 1985, the effects of row orientation were evaluated on moldboard-plow, chisel-plow, ridge-till, strip-till, and no-till systems. Under up-and-down slope conditions, runoff of alachlor and terbufos plus two metabolites (terbufos sulfoxide and terbufos sulfone) was significantly reduced by strip-till (<1% loss) compared to moldboard-plow (6% loss). Larger losses of alachlor (2% of applied) from up-and-down slope no-till than from the other conservation tillage systems (1% or less) was attributed to high concentrations in runoff associated with extensive washoff of the herbicide from soybean crop residues. With contouring, ridge tillage also was effective in reducing pesticide runoff (<1% of applied pesticide), and strip-till held losses to < 0.1%. Alachlor and carbofuran were translocated from plots largely in moving water, but terbufos and metabolites were recovered mainly in eroded sediment. Although, no conservation tillage system completely eliminated pesticide runoff, losses were most effectively minimized by contoured strip-till and no-till, which controlled both water and sediment movement.