Time domain reflectometry developments in soil science

III. Small-scale probe for measuring bulk soil electrical conductivity

Henrik H. Nissen, Paul A Ferre, Per Moldrup

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

It is commonly believed that Time Domain Reflectometry (TDR) measures bulk soil electrical conductivity (EC) and volumetric water content within the same, well-defined sample volume. However, recent studies have shown that the sample volume is a function of the distribution of EC and dielectric permittivity near the probe. One result of this spatially distributed sensitivity is measurement-induced dispersion. That is, when TDR is used to measure a sharp advancing solute front, the measured EC is some average across the sharp front, leading to incorrect smoothing of the breakthrough curve. A reduction of the probe dimensions is the only solution to this artificial smoothing problem. In this study, a small scale TDR probe is presented and tested. The small probe dimensions produce a near point measurement of EC but make water content measurements unreliable. The small scale EC TDR (SEC-TDR) probe is simple, inexpensive, and made with readily available components. A solute transport experiment was carried out under saturated conditions in a plastic pipe packed with coarse silica sand. Five SEC-TDR probes were inserted, monitoring the EC at various positions along the column, and a coaxial flow cell was used to monitor the effluent EC. Step solute breakthrough and displacement breakthrough responses were created using tap water and a KCl solution. Highly detailed measurements of EC were obtained from which the dispersivity (λ) was inferred. The λ measured by the SEC-TDR probes was significantly lower than λ measured in the effluent by the coaxial flow cell, suggesting that the SEC-TDR probe can reduce the problem of TDR-induced dispersion under even the most challenging conditions.

Original languageEnglish (US)
Pages (from-to)90-98
Number of pages9
JournalSoil Science
Volume168
Issue number2
DOIs
StatePublished - Feb 1 2003

Fingerprint

time domain reflectometry
soil science
probes (equipment)
electrical conductivity
probe
soil
smoothing
solutes
effluents
solute
plastic pipes
water content
effluent
saturated conditions
soil transport processes
dispersivity
measuring
permittivity
monitoring
breakthrough curve

Keywords

  • Electrical conductivity
  • Small-scale TDR probe
  • Solute transport
  • Time Domain Reflectometry

ASJC Scopus subject areas

  • Soil Science
  • Earth-Surface Processes

Cite this

Time domain reflectometry developments in soil science : III. Small-scale probe for measuring bulk soil electrical conductivity. / Nissen, Henrik H.; Ferre, Paul A; Moldrup, Per.

In: Soil Science, Vol. 168, No. 2, 01.02.2003, p. 90-98.

Research output: Contribution to journalArticle

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