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Soil Water Characteristic Determination from Concurrent Water Content Measurements in Reference Porous Media

^a Land Resources and Environmental Sciences Dep., Montana State Univ., P.O. Box 173120, Bozeman, MT 59717-3120
^b Plants, Soils, and Biometeorology Dep., Utah State Univ., Logan, UT 84322-4820

View larger version (28K): [in a new window]   Fig. 1. (a) Measured soil water content time series for two replicate TDR probes in Brocko and Oxisol soils in pressure chamber apparatus, and (b) the direct relationship between mean measured Brocko and Oxisol water contents, including at equilibrium pressure steps. For enhanced clarity, every tenth or every fifth data point plotted in top and middle panels respectively. Lower graph (c) shows measured and fitted soil water retention relationships obtained from measured (symbols) at pressure plate equilibrium steps, and those obtained for each soil by using the other soil as a reference medium. Inset shows same results with log matric head scale.

View larger version (20K): [in a new window]   Fig. 2. (a) Measured soil water contents at pressure equilibrium in pressure plate apparatus, for Millville silt loam and Kidman loamy sand soils. Also shown is (a) best-fit Kidman water content relationship based on the concurrent measured and known van Genuchten retention coefficients for the Millville soil. Middle panel shows (b) measured and fitted (h) for Kidman soil based on pressure plate equilibrium step measurements, and (h) obtained using Millville soil as reference porous medium in Eq. [2]. Lower panel shows converse situation: (c) measured and fitted (h) for Millville soil based on pressure plate measurements, and (h) obtained using Kidman soil as reference medium.

View larger version (41K): [in a new window]   Fig. 3. Measured time series for two replicate TDR probes in target and reference soils within the same containers (for each soil pair) in greenhouse trials. Every second data point plotted to improve clarity. For top panel (a) Kidman loamy sand reference soil pockets were buried within Flathead sandy loam, and for bottom panel (b) Millville silt loam reference soil pockets were buried within Amsterdam silt loam soil.

View larger version (27K): [in a new window]   Fig. 4. Measured volume water contents (symbols) for Amsterdam silt loam target soil plotted against concurrent measurements for Millville silt loam reference soil (data from Fig. 3b). Values are means of two TDR probes in each soil. Also shown (a) are predicted for Amsterdam soil (line) based on fitting the measured paired water contents along with known Millville soil VG retention coefficients to Eq. [2]. Lower panel shows (b) fitted (h) for Amsterdam soil based on results of two previous pressure plate measurements (symbols; Mullin unpublished data, 1999; Sperber unpublished data, 2000), and using the Millville soil as reference porous medium.

View larger version (26K): [in a new window]   Fig. 5. Measured volume water contents (symbols) for Flathead loamy sand target soil plotted against concurrent measurements for Kidman sandy loam reference soil (data from Fig. 3a). Values are means of two TDR probes in each soil. Also shown in top panel are (a) predicted for Flathead soil (line) based on fitting the measured paired water contents along with known Kidman soil van Genuchten retention coefficients to Eq. [2]. Lower panel shows (b) measured (symbols) and fitted (h) for Flathead soil determined using a pressure plate apparatus as part of a different study (Das et al. 1999), and using the Kidman soil as reference porous medium. Inset shows the same results using log matric head scale.

View larger version (26K): [in a new window]   Fig. 6. Measured time series (a) for Rothiemay loam target soil and Amsterdam silt loam reference soil at a field location near Helena, MT. Also shown (b) are the measured Rothiemay plotted against concurrent measured Amsterdam , and predicted for Rothiemay soil based on fitting the measured paired water contents along with known Amsterdam soil van Genuchten retention coefficients to Eq. [2]. Lower panel illustrates (c) measured (symbols) and fitted (thin line) (h) for Rothiemay soil based on measurements using a pressure plate apparatus as part of a different study (Sperber unpublished data, 2000), and using the Millville soil as reference porous medium in the field plots.