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Residual and Contact Herbicide Transport through Field Lysimeters via Preferential Flow

^a USDA Agricultural Research Service, National Soil Tilth Laboratory (NSTL), 2150 Pammel Drive, Ames, IA 50011
^b USDA Agricultural Research Service, North Appalachian Experimental Watershed, Coshocton, OH 43812
^c USDA Agricultural Research Service, Southeast Watershed Research Laboratory, Tifton, GA 31793
^d Formerly with USDA Agricultural Research Service, Tifton, GA 31793

View larger version (41K): [in a new window]   Fig. 1. Schematic and location of the Coshocton weighing lysimeters (not drawn to scale).

View larger version (15K): [in a new window]   Fig. 2. Lysimeter layout. The four lysimeters are designated Y103A, B, C, and D.

View larger version (32K): [in a new window]   Fig. 3. The six discrete samples collected after herbicide application in 1999. A concentration of 0.10 µg L–1 indicates not detected; a percolation rate of 0.001 mm h–1 indicates percolation rate was less than measurable.

View larger version (25K): [in a new window]   Fig. 4. Chemical concentration in percolate during the first 5.5 d after rainfall initiation (1000 h EST, 1 May 2000). The vertical lines represent the range of concentrations from the four lysimeters. The symbols represent the average alachlor and metribuzin concentration at approximately 0.06 and 0.09 d after rainfall initiation. The maximum concentrations occurred at approximately 0.10 d after rainfall initiation. Herbicide concentration determined from discrete samples except Days 2.2 and 5.5 were composite samples.

View larger version (28K): [in a new window]   Fig. 5. Logarithmic presentation of 2000 average concentration with 95% confidence intervals. Note that log(1) = 0, therefore the y intercept is at 1.00 d after rainfall initiation. Time zero is 1000 h EST, 1 May 2000 (rainfall initiation). The symbols represent the average alachlor and metribuzin concentration from the four lysimeters.