PAIRED WATERSHED COMPARISON OF TILLAGE EFFECTS ON RUNOFF, SEDIMENT, AND PESTICIDE LOSSES

A paired watershed study was used to compare runoff, sediment, atrazin e (2-chloro-4-ethylamino-6-isopropylamino-1,3,5 triazine), and cyanazi ne loro-6-(ethylamino)-S-triazin-2-yl]amino]-2-methyl propionitrile) l osses from conventional-tilled (CT) and reduced-tilled (RT) corn (Zea mays L.) watersheds. During a 13-mo calibration period both watersheds were moldboard plowed and runoff was measured in H-flumes. Composite samples were analyzed for sediment and for atrazine and cyanazine in d issolved and sediment phases. During a 30-mo treatment period, one wat ershed was moldboard plowed while the other was disk harrowed. Reduced tillage decreased runoff by 64% and sediment losses by 99% but did no t change dissolved atrazine or cyanazine concentrations in runoff. Con centrations of sediment-sorbed pesticides increased in runoff. The RT reduced mass losses of atrazine and cyanazine in runoff, primarily bec ause of decreases in runoff volume and sediment mass. Most pesticide l osses occurred within 3 wk of field application. Pesticide loss was pr imarily in the dissolved phase. The paired watershed approach was a us eful technique for determining watershed treatment effects when differ ences existed between watersheds chosen for study.