Submitted to: Symposium on the Fate and Chemistry of Modern Pesticides Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 15, 2004
Publication Date: August 16, 2004
Citation: Ghidey, F., Alberts, E.E., Lerch, R.N., Kitchen, N.R., Sadler, E.J. 2004. Cropping system effects on herbicide transport in surface runoff from a claypan soil. ii. field-scale case studies. Symposium on the Fate and Chemistry of Modern Pesticides Proceedings. Technical Abstract: Surface transport of herbicides in the claypan soil watersheds of Missouri has been shown to contaminate streams and drinking water reservoirs throughout the region, especially during the spring. A long-term study was implemented in 1992 to evaluate the fate and transport of some common soil-applied corn and soybean herbicides from farm fields. In this study, herbicide concentrations in surface runoff from three field-size watersheds (6-30 ha) located in the claypan soil region of north-central Missouri were measured from 1993-1997. During each runoff event, water samples were collected at equal flow intervals from the outlets of the drainage areas and analyzed for atrazine, alachlor, and metolachlor. Herbicide concentrations in surface runoff declined exponentially from >100 ug L**-1 within a few days after application to < 1.0 ug L**-1 after 8 weeks. More than 90% of the annual herbicide loss occurred within 4 weeks following application, and nearly 100% of herbicide loss occurred within 8 weeks after application. Atrazine and alachlor (or metolachlor) losses to surface runoff accounted for 8.7 and 3.6% of the total applied in the soil when herbicide was surface applied and not incorporated, and 1.4 and 1.0% when herbicide was surface applied and incorporated, respectively. Occurrence of rainfall relative to application and incorporation of herbicides were two of the main factors controlling transport at the field scale. A generalized model will be developed from these data and similar data obtained from replicated plots to predict herbicide concentrations and load in runoff from herbicide-treated fields. Overall, this study showed that the critical herbicide loss period was the 2 months following application, and most losses occurred within 1 month of application.