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ORIGINAL RESEARCH

Comparison of Capacitance-Based Soil Water Probes in Coastal Plain Soils

USDA-ARS, Southeast Watershed Research Laboratory, P.O. Box 748, Tifton, GA 31793
^* Corresponding author (dbosch{at}tifton.usda.gov)

Received 22 January 2004.

Soil water influences infiltration and runoff and consequently water quality. In situ measurements of soil water are critical for understanding hydrologic and water quality processes. Many advances have recently been made in soil water measurement techniques. In particular, instruments for estimating volumetric water content from measurements of soil electrical properties have become common. While the instruments have been shown to be good indicators of relative changes in soil water, questions remain regarding their ability to yield quantitative estimates. Most of these techniques rely on a limited set of calibration equations obtained through laboratory analysis of homogeneous soil materials (i.e., sand, silt, and clay). The accuracy of two capacitance-based soil water probes was assessed for a range of Coastal Plain soils. The probes measure capacitive and conductive soil properties and relate these to water content through calibration. Calibration curves for three different Coastal Plain soils were developed. Laboratory tests indicate that the probes yield estimates of volumetric water content within ±0.05 cm³ cm^–3 of the observed values for these soils. Greater variability was observed in comparisons with field observations. Results indicate that improved equations can be developed through soil-specific laboratory calibration. The capacitance probes should prove to be useful tools for estimating volumetric water content in these soils. Additional work is required to quantify probe differences and the effects of soil conductivity on the measurements.

Abbreviations: MSE, mean square error • TDR, time domain reflectometry

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