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Impact of Preferential Flow at Varying Irrigation Rates by Quantifying Mass Fluxes

^a Hydrology and Remote Sensing Laboratory, USDA-ARS, BARC-West, 10300 Baltimore Boulevard, Beltsville, MD 20705-2350
^b Alternate Crops and Systems Laboratory, USDA-ARS, BARC-West, 10300 Baltimore Boulevard, Beltsville, MD 20705-2350
^c Agronomy Department, University of Wisconsin, Madison, WI 53706-1299
^d Department of Biological System Engineering, University of Wisconsin, Madison, WI 53706-1299
^e Civil Engineering Department, Santa Clara University, 500 Camino Real, Santa Clara, CA 95053
^f Department of Agronomy, Purdue University, West Lafayette, IN 47906
^g Department of Agricultural and Biological Engineering, Cornell University, Ithaca, NY 14853

View larger version (57K): [in a new window]   Fig. 1. Experimental site location.

View larger version (31K): [in a new window]   Fig. 2. Schematic of the tile-drained facility.

View larger version (48K): [in a new window]   Fig. 3. Water flux and Br breakthrough curves. The red line represents water flux while the blue line denotes bromide mass flux as a function of time after application. Bromide mobile tracer was subjected to a 4.4 mm h–1 irrigation rate.

View larger version (56K): [in a new window]   Fig. 4. Water and pentafluorobenzoic acid (PFBA) breakthrough curves. The red line represents water flux while the black line denotes PFBA mass flux as a function of time after application. The PFBA mobile tracer was subjected to a 0.89 mm h–1 irrigation rate. The green line represents the best fit line using the one-dimensional convective–dispersive equation (CDE).

View larger version (40K): [in a new window]   Fig. 5. Comparison of Br and pentafluorobenzoic acid (PFBA) breakthrough curves as a function of water applied. The blue line represents the Br breakthrough pattern at an irrigation rate of 4.4 mm h–1 while the black line denotes the PFBA breakthrough pattern at an irrigation rate of 0.89 mm h–1. The orange line represents the best fit line using the one-dimensional convective–dispersive equation (CDE) of the PFBA data. Solute recoveries and transport fitting are a function of cumulative water applied since tracer application.

View larger version (51K): [in a new window]   Fig. 6. Effect of increased dispersion relative to Br and pentafluorobenzoic acid (PFBA) breakthrough curves. Solute fluxes shown as a function of time after application. Blue and black lines represent Br and PFBA breakthrough patterns at irrigation rates of 4.4 and 0.89 mm h–1, respectively. The orange line represents the best fit line using the one-dimensional convective–dispersive equation (CDE) on the lower irrigation rate (PFBA) while at the higher irrigation rate (Br) transport simulations were conducted by increasing the dispersion coefficient by 2 (gold line) and 10 times (pink line).