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Water and Solute Transport in a Cultivated Silt Loam Soil

2. Numerical Analysis

Y. Coquet^a,*, J. imnek^b, C. Coutadeur^a, M. Th. van Genuchten^c, V. Pot^a and J. Roger-Estrade^d

^a UMR INRA/INAPG Environment and Arable Crops, Institut National de la Recherche Agronomique/Institut National Agronomique Paris-Grignon, B.P. 01, 78850 Thiverval-Grignon, France
^b Dep. of Environmental Sciences, Univ. of California, Riverside, CA 92521
^c USDA-ARS, George E. Brown, Jr. Salinity Lab., 450 West Big Springs Road, Riverside, CA 92507
^d UMR INRA/INAPG Agronomy, Institut National de la Recherche Agronomique/Institut National Agronomique Paris-Grignon, B.P. 01, 78850 Thiverval-Grignon, France

View larger version (88K): [in a new window]   Fig. 1. Soil profile perpendicular to the tillage direction showing the different structural components of the plow layer (the untilled soil does not appear on the photo). Compacted zones are delineated by solid white lines. Also shown in (a) are locations of the TDR probes (circles) and tensiometers (squares), while (b) shows the spatial distribution of the different soil structure types used in the HYDRUS-2D model.

View larger version (26K): [in a new window]   Fig. 2. Soil water retention, (h) (top) and unsaturated hydraulic conductivity, K(h) (bottom) curves for the four soil structure types: (a) seed bed, (b) macroporous structure, (c) compacted structure, and (d) subsoil as determined using tension infiltrometry (open triangle), Wind's evaporation method (open diamond), a constant-head method (open square), and using pressure plates (open circle). Solid curves represent the fitted Mualem-van Genuchten functions. Measured values for Ks were plotted on the left axes at log(–h) = –2, where h is in cm (or hPa).

View larger version (40K): [in a new window]   Fig. 3. Measured (symbols) and simulated (lines) water contents of the four different soil structure types: (a) seed bed, (b) compacted structure, (c) untilled subsoil below the wheel tracks, (d) macroporous structure, and (e) untilled subsoil between the wheel tracks. Vertical grid lines indicate time period during which bromide was applied with the infiltrating water. Numerical simulations were performed using the independently estimated soil hydraulic parameter values in Table 1.

View larger version (30K): [in a new window]   Fig. 4. Measured (symbols) and simulated (lines) pressure heads of the four different soil structure types: (a) seed bed, (b) compacted structure, (c) macroporous structure, and (d) untilled subsoil. Numerical simulations were performed using the independently estimated soil hydraulic parameter values in Table 1.

View larger version (21K): [in a new window]   Fig. 5. Comparison of retention curves measured in the laboratory using the evaporation method, and field-measured water contents and pressure heads for four types of soil structures: (a) seed bed, (b) macroporous structure, (c) compacted structure, and (d) untilled subsoil. White squares in (d) are data from an independent internal drainage experiment (Nicole, 2000).

View larger version (45K): [in a new window]   Fig. 6. Contours of measured (a) and calculated (b) bromide concentrations 12 h after irrigation. Simulated values were obtained using the independently estimated hydraulic parameter values in Table 1.

View larger version (27K): [in a new window]   Fig. 7. Measured (symbols) and simulated (lines) bromide concentration profiles at two locations with the shallowest (a) and deepest (b) simulated solute fronts 12 h after irrigation (x = 78 cm is below the wheel tracks, and x = 190 cm is between the wheel tracks). Simulated values were obtained using the independently estimated hydraulic parameter values in Table 1.

View larger version (37K): [in a new window]   Fig. 8. Measured (symbols) and simulated (lines) water contents in the four types of soil structure: (a) seed bed, (b) compacted structure, (c) untilled subsoil below the wheel tracks, (d) macroporous structure, and (e) untilled subsoil between the wheel tracks. Vertical grid lines indicate time period during which bromide was applied with the infiltrating water. Simulated values were obtained using the optimized soil hydraulic parameter values in Table 2.

View larger version (46K): [in a new window]   Fig. 9. Contours of measured (a) and calculated (b) bromide concentrations 12 h after irrigation. Simulated values were obtained using the adjusted hydraulic parameter values in Table 2.

View larger version (36K): [in a new window]   Fig. 10. Measured and simulated concentration profiles versus depth at selected locations. Simulated values were obtained using the adjusted hydraulic parameter values listed in Table 2.