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DIURON OCCURRENCE AND DISTRIBUTION IN SOIL AND SURFACE AND GROUND WATER ASSOCIATED WITH GRASS SEED PRODUCTION
Field, J. A., R. L. Reed, T. E. Sawyer, S. M. Griffith, AND P. J. WIGINGTON JR. DIURON OCCURRENCE AND DISTRIBUTION IN SOIL AND SURFACE AND GROUND WATER ASSOCIATED WITH GRASS SEED PRODUCTION. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, WI, 32(1):171-179, (2003).
Diuron (3-(3,4-dichlorophenyl)-1,1-dimethyl urea) is the principal herbicide used in grass seed production. The occurrence and distribution of diuron was investigated at a poorly-drained field site located along an intermittent tributary of Lake Creek in the southern Willamette Valley of Oregon. The experimental sites consisted of a field under commercial grass seed production with a cultivated riparian zone and a second site that was part of the same grass seed field but with a non-cultivated riparian zone. Diuron and its metabolites were determined in samples of surface water, shallow and deep groundwater, and soil collected from the two study sites. Diuron and its metabolite DCPMU were the only significant residues detected in this study, while DCPU, DCA, and its dechlorination products were not detected. Concentrations of diuron and DCPMU in surface water declined from a maximum immediately following application to low levels that persisted as long as flow was present. Diuron and DCPMU concentrations in shallow groundwater were highest in the zone immediately adjacent to Lake Creek, which indicates the influence of stream water on shallow groundwater near the stream. Concentrations of diuron were lower in shallow groundwater within the noncultivated riparian zone than in the cultivated riparian zone. However, very little groundwater moves through the soil A horizon at this site so the influence of the noncultivated riparian zone on stream water quality is limited. The combined concentrations of diuron and DCPMU in soil were found to be equal to or greater than the diuron application rate, which indicates that diuron residues persist in soil. Surface runoff during the rainy season removes a very small percentage of the applied herbicide.