Effect of Tillage System on Runoff Losses of Surface‐applied Pesticides

Four tillage systems (conventional, chisel, ridge-plant, and no-till) in continuous corn (Zea mays L.) were compared with respect to surface runoff losses of atrazine (2-chloro-4-ethyl-amino-6-isopropylamino-s-triazine), alachlor [2-chloro-2′6′-diethyl-N(methoxymethyl) acetanilide] and chlorpyrifos [O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate]. A modified Purdue sprinkling infiltrometer was used to apply simulated rainfalls of 136 and 73 mm during the 1983 and 1984 growing seasons to 1.35-m² test areas on a Griswold silt loam (Typic Argiudoll). Conservation tillage (CT) systems (chisel, ridge-plant, and no-till) reduced both runoff and soil loss; however, pesticide concentrations in runoff water and sediment for these systems were at times greater than for the conventional (moldboard plow) system. Reduced runoff volumes and erosion with CT systems offset higher pesticide concentrations resulting in few significant tillage treatment differences with respect to total pesticide loss. Maximum loss of active ingredient averaged over all tillage systems was 5.8, 4.0, and 0.2% for atrazine, alachlor, and chlorpyrifos, respectively, when high-intensity simulated rainfall was applied within 7 d of pesticide application.