HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Logsdon, S. Search for Related Content PubMed Articles by Logsdon, S. GeoRef GeoRef Citation Agricola Articles by Logsdon, S. Related Collections Water Content Data Assimilation

SPECIAL SECTION: SOIL WATER SENSING

Time Domain Reflectometry Range of Accuracy for High Surface Area Soils

National Soil Tilth Laboratory, 2150 Pammel Dr., Ames, IA 50011
^* Corresponding author (logsdon{at}nstl.gov)

Received 15 July 2004.

Time domain reflectometry (TDR) is commonly used to determine water content. Many laboratory studies have shown accurate water determination across a wide range of soils, often with a unified calibration equation. Recent data has shown a strong temperature influence on some TDR data. The purpose of this study was to calibrate TDR for water content under both laboratory and field conditions for Mollisols. TDR waveguides and thermocouples were installed horizontally into the sides of pits at four sites and 9 or 10 depth positions on a 5% slope. Neutron access tubes were installed within 3.3 m of the TDR sites. After the field study, soil was collected around the waveguides and repacked into columns for laboratory calibration. The columns were progressively wetted and then dried over a few months. At each water content and at two or three temperatures, the waveforms, bulk electrical conductivity, and square root of apparent dielectric were saved for the laboratory data, but memory limitations prevented saving waveforms from the field data. Much of the field calibration data were shifted to higher values for _a^1/2 than for the laboratory data, apparently due to problems with internal waveform analysis. High bulk electrical conductivities (up to 0.13 S m^–1) were apparent for some of the sites and depths even though these are not saline soils. For the laboratory data, adding a temperature term to the calibration equation reduced the root mean square error (378 data points) from 0.54 to 0.34 m³ m^–3, and for the field data (939 points) reduced it from 0.78 to 0.54 m³ m^–3.

Abbreviations: TDR, time domain reflectometry

This article has been cited by other articles:

				M. S. Seyfried and L. E. Grant Temperature Effects on Soil Dielectric Properties Measured at 50 MHz Vadose Zone J., October 8, 2007; 6(4): 759 - 765. [Abstract] [Full Text] [PDF]

				S. D. Logsdon Experimental Limitations of Time Domain Reflectometry Hardware for Dispersive Soils Soil Sci. Soc. Am. J., February 27, 2006; 70(2): 537 - 540. [Abstract] [Full Text] [PDF]

				S. R. Evett and G. W. Parkin Advances in Soil Water Content Sensing: The Continuing Maturation of Technology and Theory Vadose Zone J., November 11, 2005; 4(4): 986 - 991. [Abstract] [Full Text] [PDF]