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United States Department of Agriculture

Agricultural Research Service

Title: Site Specific Evaluation of Multisensor Capacitance Probes

Authors
item Rowland, Randy
item Guber, Andrey
item PACHEPSKY, YAKOV
item Gish, Timothy
item DAUGHTRY, CRAIG

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: September 24, 2007
Publication Date: December 14, 2007
Citation: Rowland, R.A., Guber, A.K., Pachepsky, Y.A., Gish, T.J., Daughtry, C.S. 2007. Site Specific Evaluation of Multisensor Capacitance Probes. Fall Meeting of the American Geophyscial Union, December 10-14, 2007, San Francisco, CA. H51C-0646.

Technical Abstract: Multisensor capacitance probes (MCPs) are widely used for measuring soil water content (SWC) at the field scale. Although manufacturers supply a generic MCP calibration, many researchers recognize that MCPs should be calibrated for specific field conditions. MCPs measurements are typically associated with small soil volumes, and are subsequently scaled up to the plot or field scale. Research is needed to understand how representative are these measurements for water monitoring studies that operate with the elementary area from one to tens square meters The objectives of this study were: (a) to test the accuracy of SWC field measurements using generic and laboratory MCP calibrations; (b) to test applicability of a single MCP calibration for SWC measurements at different depths; and (c) to compare the accuracy of two and three-parameter equations using scaled frequency (SF). Four 1x1 m plots were equipped with MCPs to measure SWC at 9 depths at the OPE3 USDA-ARS research site at Beltsville, MD. Within each plot, three undisturbed soil cores were taken with a 100 cm3 soil auger. SWC sampling was made on three different dates when soil water contents were distinctly different. To compare MCP measurements with observed SWC, the SF was converted into SWC using: (a) the manufacturer generic calibration, and (b) calibration obtained in laboratory for a mesic Aquic Hapludult soil. Parameters of three different calibration equations were also obtained by fitting the equations to the water contents measurements at the plots. This fit was done: (a) for all observations regardless the depth, (b) for observations at each genetic horizon, and (c) for each depth separately. Results show that the manufacturer and the laboratory calibrations provided a satisfactory fit to the field-measured SWC at depths of 30, 40 and 50 cm. The fit was about two times less accurate at depths of 10, 20, 60, 70 80 and 90 cm. A minor improvement was obtained at depths of 10 and 20 cm after calibration equations were parameterized with observations from all depths pooled together. A significant improvement (P<0.02) in accuracy of MCP measurements for depths of 10, 20, 60 and 70 cm was obtained after SWC data were grouped into subsets either according to soil genetic horizon or according to depth. The three-parameter calibration equations did not improve accuracy compared to two-parameter calibration equations. Overall, more accurate measurements of SWC in a layered soil using MCPs could be obtained by employing site and depth-specific relationships between SF and plot-averaged water contents.

Last Modified: 9/10/2014
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