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Laboratory Evaluation of a Commercial Dielectric Soil Water Sensor

^a USDA-ARS, 3810 4th Street, Lubbock, TX 79415
^b Texas A&M University, 3810 4th Street, Lubbock, TX 79415

View larger version (58K): [in a new window]   Fig. 1. Experimental setup of ECH2O probes and thermocouples inside a PVC cylinder filled with soil (not to scale).

View larger version (30K): [in a new window]   Fig. 2. Output of an ECH2O probe in deionized water as a function of increasing and decreasing temperature. The arrows indicate the order of ascending or descending temperature.

View larger version (22K): [in a new window]   Fig. 3. Measured soil volumetric water content (VWC) as a function of depth at an average soil VWC of 0.038, 0.198, and 0.247 m3 m-3, respectively, on three separate cylinders.

View larger version (26K): [in a new window]   Fig. 4. Output of an ECH2O probe as a function of day of year (DOY, 2002) and different soil volumetric water content (VWC) at a constant soil temperature of 26.4°C. At a soil VWC of 0.15 m3 m-3 the soil temperature varied between 15.5 and 39.1°C. The vertical dashed lines represent the time when water was added to the PVC cylinder.

View larger version (16K): [in a new window]   Fig. 5. ECH2O output as a function of soil volumetric water content (VWC), where temperature varied between 14.5 and 39.0°C at each water level. The vertical bars at each VWC represent the distribution of individual data points for the temperature variation.

View larger version (30K): [in a new window]   Fig. 6. ECH2O output as a function of soil volumetric water content (VWC) for two soils and a potting material all at a constant temperature of 24.5°C: (a) Amarillo-2, (b) Pullman, and (c) fritted clay. The vertical bars represent the distribution of individual data points at each soil VWC.

View larger version (21K): [in a new window]   Fig. 7. Temperature sensitivity of ECH2O probes output as a function of changes in soil volumetric water content (VWC) in a fine sandy loam soil.