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Measurement of Soil Water Content with a 50-MHz Soil Dielectric Sensor

USDA-ARS, 800 Park Blvd., Plaza IV, Boise, ID 83712

View larger version (26K): [in a new window]   Fig. 1. Real (r) and imaginary (i) components of the complex dielectric constant for different KCl solution concentrations. The HP label refers to Hydra Probe. Each point represents the average of the three sensors. Error bars data indicate the measurement range among the three sensors. Individual response remained precise relative to sensor differences. Deviations were more extreme at concentrations >0.05 M.

View larger version (28K): [in a new window]   Fig. 2. The measured real dielectric constant (r) using three Hydra Probe sensors (S1, S2, and S3) compared with the Topp equation as affected by soil water content for (a) the sand soil, (b) Summit soil, (c) Sheep Creek soil, and (d) Foothill soil.

View larger version (17K): [in a new window]   Fig. 3. Comparison of manufacturer supplied calibration curves, labeled sand, silt, clay, and the Topp equation.

View larger version (30K): [in a new window]   Fig. 4. Effect of temperature on measured real dielectric constant (r) for the three sensors tested (S1, S2, and S3), in oven-dry (dry) and near saturated (wet) soil conditions for (a) sand soil, (b) Summit soil, (c) Sheep Creek soil, and (d) Foothill soil. Dense concentrations of points occur where the rate of temperature change was slow.

View larger version (17K): [in a new window]   Fig. 5. Loss tangent (tan ) of four soils as a function of soil water content. Curves were generated from best-fit polynomial equations of r and i for each soil.

View larger version (18K): [in a new window]   Fig. 6. Effect of temperature on i for the four soils measured at nearly saturated soil water contents with Sensor S2.