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a Department of Bioengineering, Oregon State University, Corvallis, OR 97331
b Department of Horticulture, Oregon State University, Corvallis, OR 97331
c present address: Camp, Dresser & McKee, 11811 NE 1st Street, Suite 201, Bellevue, WA 98005.
* Corresponding author (david.rupp{at}lifetime.oregonstate.edu)
Received for publication March 11, 2005. The typical method of cool-season grass-seed production in Mediterranean climates briefly exposes surface waters to potentially high concentrations of the herbicide diuron [3-(3,4-dichlorophenyl)-1,1-dimethyl urea] during the initial season of growth. To better understand the process, and the degree, of diuron transport from agricultural fields, two grass-seed fields in the Willamette Valley of Oregon were monitored for diuron loss in surface runoff and tile drainage during the first wet season after planting. Initial diuron concentrations in surface runoff were high (>1000 µg L1 in one field and >100 µg L1 in the other), though they decreased by two orders of magnitude by the end of the season. Concentrations in the tile drains were as much as 1000 times lower than in the surface runoff during the first few weeks of runoff events, and they remained lower than surface water concentrations throughout the season. Total losses in surface runoff were between 1.3 and 3% of the amount appliedmuch higher than losses via the tile drains. It is also shown by means of a simple first-order decay model that, when little information is available, it may be best to describe diuron depletion in runoff water as a function of cumulative rainfall during the wet season.
Abbreviations: DCPMU, 3-(3,4-dichlorophenyl)-1-methyl-urea OC%, percentage organic carbon
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