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Calibration of the Root Zone Water Quality Model for Simulating Tile Drainage and Leached Nitrate in the Georgia Piedmont

^a USDA-ARS-JPCNRCC, Watkinsville, GA 30677
^b Dep. of Crop and Soil Sci., Univ. of Georgia, Athens, GA 30602-7274
^c Usda-Ars-Grl, El Reno, Ok 73036
^d Usda-Ars-Ngprl, Mandan, Nd 58554
^e USDA-NRCS-ITC, Fort Collins, CO 80526-8121
^f Dupont Research, Wilmington, DE 19898
^g Biol. and Agric. Eng. Dep., Univ. of Georgia, Griffin, GA 30223-1797

View larger version (21K): [in a new window]   Fig. 1. Tile drainage system as set up in the RZWQM to emulate the design at the study site where z' = depth of drains, = distance from the water table to the impermeable layer, m = water table height above the drains, d = distance from the drain to the impermeable layer, and L = distance between drains. Design is based on the Hooghoudt steady state equation to estimate the flux at the center of the drains and correct for two-dimensional flow.

View larger version (30K): [in a new window]   Fig. 2. Flow chart of procedure used to calibrate and evaluate the Root Zone Water Quality Model.

View larger version (34K): [in a new window]   Fig. 3. Simulations using values of ground water leakage rate, vw, for sensitivity analysis of simulated tile drainage and leached nitrate.

View larger version (50K): [in a new window]   Fig. 4. Cumulative observed and simulated tile drainage (top) and leached nitrate (bottom) with and without macroporosity for the simulation period November 1992 through April 1993 for maize.

View larger version (32K): [in a new window]   Fig. 5. Measured and simulated event tile drainage (top) and leached nitrate (bottom) for the simulation period from November 1992 through April 1993 with and without the macroporosity option for maize. Observed drainage events shown with 95% C.I. bars.

View larger version (21K): [in a new window]   Fig. 6. Observed and simulated cotton biomass development with and without the macroporosity option in the model.

View larger version (33K): [in a new window]   Fig. 7. Observed soil moisture and rainfall and simulated soil moisture with and without macroporosity for the cotton growing season in 1997.