title: Tillage system, application rate, and extreme event effects on herbicide losses in surface runoff.
abstract: Conservation tillage can reduce soil loss; however, the residual herbicides normally used to control weeds are often detected in surface runoff at high levels, particularly if runoff-producing storms occur shortly after application. Therefore, we measured losses of alachlor, atrazine, linuron, and metribuzin from seven small (0.45-0.79-ha) watersheds for 9 yr (1993-2001) to investigate whether a reduced-input system for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production with light disking, cultivation, and half-rate herbicide applications could reduce losses compared with chisel and no-till. As a percentage of application, annual losses were highest for all herbicides for no-till and similar for chisel and reduced-input. Atrazine was the most frequently detected herbicide and yearly flow-weighted concentrations exceeded the drinking water standard of 3 microg L(-1) in 20 out of 27 watershed years that it was applied. Averaged for 9 corn yr, yearly flow-weighted atrazine concentrations were 26.3, 9.6, and 8.3 microg L(-1) for no-till, chisel, and reduced-input, respectively. Similarly, flow-weighted concentrations of alachlor exceeded the drinking water standard of 2 microg L(-1) in 23 out of 54 application years and in all treatments. Thus, while banding and half-rate applications as part of a reduced-input management practice reduced herbicide loss, concentrations of some herbicides may still be a concern. For all watersheds, 60 to 99% of herbicide loss was due to the five largest transport events during the 9-yr period. Thus, regardless of tillage practice, a small number of runoff events, usually shortly after herbicide application, dominated herbicide transport.
authors.affiliation: USDA-Agricultural Research Service, North Appalachian Experimental Watershed, P.O. Box 488, Coshocton, OH 43812-0488, USA. martin@coshocton.ars.usda.gov
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Shipitalo
authors.forename: Lloyd B
authors.initials: LB
authors.lastname: Owens
mesh_terms: D000081:Acetamides / Q000032:analysis; D000383:Agriculture; D001280:Atrazine / Q000032:analysis; D004784:Environmental Monitoring; D006540:Herbicides / Q000032:analysis*; D007700:Kinetics; D008044:Linuron / Q000032:analysis; D011891:Rain; D012989:Soil Pollutants / Q000032:analysis*; D013025:Glycine max / Q000254:growth & development; D014227:Triazines / Q000032:analysis; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply; D003313:Zea mays / Q000254:growth & development
chemical_list: D000081:Acetamides; D006540:Herbicides; D012989:Soil Pollutants; D014227:Triazines; D014874:Water Pollutants, Chemical; D008044:Linuron; C000188:alachlor; D001280:Atrazine; C009235:metribuzin