Field evaluation of a soil water-capacitance probe in a fine sand
1995
TOMER, M. D. | Anderson, J. L.
A soil water capacitance probe (C-probe) and a neutron probe (N-probe) were calibrated for a fine sand. Data obtained with both probes and by time domain reflectometry (TDR) were compared. Calibrations were linear for the N-probe (R = 0.97), and quadratic for the C-probe (R = 0.92), based on 30 samples varying from 0.03 to 0.30 volumetric water content. N-probe-measured water contents were better correlated with TDR-measured water contents (R = 0.92) than were C-probe measurements (R = 0.80). Water-content profiles were measured with both probes in 79 access tubes seven times during the summer of 1992. The C-probe gave greater soil-water estimates than the N-probe, particularly at depths less than 70 cm. Measured water depletion (in 1.5 m profiles over 2 weeks) averaged 1.2 cm less for the C-probe than the N-probe. For dry or coarse textured soils, changes in water content are difficult to detect with the C-probe. This is partly because of the dielectric response measured by the C-probe: the calibration shows a decreasing slope with lesser water content. The C-probe also measures a smaller soil volume than the N-probe. This provides improved depth resolution, but the C-probe is more sensitive to localized conditions, including disturbance effects resulting from access tube installation.
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