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Simultaneous Measurement of Soil Penetration Resistance and Water Content with a Combined Penetrometer–TDR Moisture Probe

^a EMBRAPA, Agricultural Instrumentation, P.O. Box 741, Sao Carlos-SP, 13560-970, Brazil
^b Department of Land, Air and Water Resources, Hydrology Program, 123 Veihmeyer Hall, University of California, Davis, CA 95616

View larger version (50K): [in a new window]   Fig. 1. Detailed (A) diagram and (B) a cross section of the coiled time domain reflectometry (TDR) and (C) the conventional TDR probe

View larger version (15K): [in a new window]   Fig. 2. Combined coiled time domain reflectometry (TDR)–cone penetrometer probe

View larger version (20K): [in a new window]   Fig. 3. Representative waveforms for the (a) coiled time domain reflectometry (TDR) and (b) conventional probe designs for the three investigated soil materials at water contents values of 0.05 and 0.20 cm3 cm-3. Vertical lines mark the first and second reflection points

View larger version (16K): [in a new window]   Fig. 4. Relationship between dielectric constant as measured by the coiled (coil) and conventional (soil) time domain reflectometry (TDR) probes for investigated soils

View larger version (21K): [in a new window]   Fig. 5. Calibration data for the conventional time domain reflectometry (TDR) probe, using Eq. [2] for all three soil types (from average values of bulk density and porosity in Table 1), and compared with Topp's (1980) model. Range in water content is identical to that in Fig. 4 and 6

View larger version (20K): [in a new window]   Fig. 6. Calibration data for the coiled TDR probe using Eq. [3] for all three soil types (from average values of bulk density and porosity in Table 1), using parameters n, w, probe fitted to Eq. [1] and soil specific values fitted to Eq. [2]. Fitted polynomial is used for field measurements

View larger version (55K): [in a new window]   Fig. 7. Combined field measurement results of penetration resistance (PR) and water content () obtained with the combined coiled time domain reflectometry (TDR)–cone penetrometer probe for the Yolo soil

View larger version (27K): [in a new window]   Fig. 8. Independent values for dry soil bulk density and water content for the Yolo soil in the field, determined from gravimetric measurements of soil core samples collected at the same plot of the combined penetrometer–coiled time domain reflectometry (TDR) probe measurements

View larger version (15K): [in a new window]   Fig. 9. Correlation between water content measured by the coiled time domain reflectometry (TDR) probe (coil) and gravimetric data from collected soil cores for the Yolo field soil