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United States Department of Agriculture

Agricultural Research Service

Title: Time Domain Reflectometry Range of Accuracy for High Surface Area Soils

Author
item Logsdon, Sally

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 4, 2004
Publication Date: November 4, 2004
Citation: Logsdon, S.D. 2004. Time domain reflectometry range of accuracy for high surface area soils [CD-ROM]. ASA-CSSA-SSSA Annual Meeting Abstracts. Madison, Wisconsin.

Technical Abstract: Time domain reflectometry (TDR) is commonly used to determine water content. Recent data has shown a strong diurnal temperature influence on TDR data. The purpose of this study was to calibrate TDR for water content under both laboratory and field conditions, showing seasonal temperature effects. TDR waveguides and thermocouples were installed horizontally into the sides of pits at 4 sites with 10 depths at each site. Neutron access tubes were installed within 3.3 m of each of the TDR sites. After the field study, soil was collected around the waveguides and repacked into columns in the laboratory. Waveguides were installed into the columns, which were then progressively wetted and then dried over a few months. At each water content, data were collected at two or three temperatures. Some of the field data for square root of apparent dielectric was correlated more strongly with temperature than with water content. Much of the field calibration data were shifted to higher dielectric values than for the laboratory data, due to problems with internal waveform analysis. High bulk electrical conductivities were apparent for some of the sites and depths even though these are not saline soils. Adding a temperature term to the calibration equation decreased the difference between measured and calculated water content, and is recommended for field TDR data analysis of water content.

Last Modified: 11/24/2014
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