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This article in SSSAJ

  1. Vol. 70 No. 2, p. 533-536
     
    Received: June 30, 2005


    * Corresponding author(s): magnus.persson@tvrl.lth.se
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doi:10.2136/sssaj2005.0209N

A Small-Scale Matric Potential Sensor Based on Time Domain Reflectometry

  1. Magnus Persson *a,
  2. Jon M. Wraithb and
  3. Torleif Dahlinc
  1. a Dep. of Water Resources Engineering, Lund Univ., Box 118, SE-221 00 Lund, Sweden
    b Land Resources and Environmental Sciences Dep., Montana State Univ., P.O. Box 173120, Bozeman, MT 59717-3120, USA
    c Engineering Geology, Lund Univ., Box 118, SE-221 00 Lund, Sweden

Abstract

Measurements of soil matric potential (ψ) are needed in many soil science applications. In the present study, a small matric potential sensor having a length of 30 mm and a diameter of 9.6 mm was developed. The sensor consists of two coils made of lacquer-coated copper wires embedded in gypsum. The dielectric constant of the gypsum (K gypsum) was measured with time domain reflectometry (TDR). The gypsum probes were tested in a sandy loam soil using a pressure extractor to obtain the relationship between K gypsum and ψ, allowing inference of the soil ψ in equilibrium with the sensor. It was shown that the gypsum probe could give ψ estimates with a root mean square error (RMSE) of around 50 kPa in the range of −20 to −1500 kPa. Most of the sensitivity of the sensor was in the −50- to −1000-kPa range.

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Copyright © 2006. Soil Science SocietySoil Science Society of America