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Soil Science Society of America Journal Abstract - SOIL PHYSICS

Measurement of Low Matric Potentials with Porous Matrix Sensors and Water-Filled Tensiometers


This article in SSSAJ

  1. Vol. 73 No. 6, p. 1796-1803
    Received: Dec 5, 2008

    * Corresponding author(s): richard.whalley@bbsrc.ac.uk
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  1. W. R. Whalley *a,
  2. G. Lockb,
  3. M. Jenkinsb,
  4. T. Peloeb,
  5. K. Burekb,
  6. J. Balendonckc,
  7. W.A. Taked,
  8. İ.H. Tuzele and
  9. Y. Tuzele
  1. a Rothamsted Research, West Common, Harpenden, St Albans, AL5 2JQ UK
    b Delta-T Devices, 130 Low Road, Burwell, Cambridge, CB25 OEJ, UK
    c Wageningen UR, Greenhouse Horticulture, PO Box 644, 6700 AP Wageningen, Droevedaalsesteeg 16708 PB Wageningen, the Netherlands
    d Department of Civil Engineering, Queen's University, Kingston, ON, K7L 3N6, Canada
    e Ege University, Faculty of Agriculture, Bornova, Izmir, Turkey


Water-filled tensiometers are widely used to measure the matric potential of soil water. It is often assumed that, because these give a direct reading, they are accurate. With a series of laboratory tests with model laboratory systems of increasing complexity we show that the output of water-filled tensiometers can, particularly in drying soils, be in serious error. Specifically, we demonstrated that water-filled tensiometers can indicate a steady matric potential, typically between −60 and −90 kPa, when the soil is much drier. We demonstrate the use of water-filled tensiometers that can measure matric potentials smaller than −100 kPa in the laboratory and in the field. The physics of the failure of water-filled tensiometers is discussed. When the matric potential was greater than −60 kPa, in laboratory and field tests water-filled and porous matrix sensors were in good agreement. In the field environment the porous matrix sensor was useful because it allowed early detection of the failure of water-filled tensiometers. In dry soils (matric potential < −60 kPa) the porous matrix sensor was more reliable and accurate than the water-filled tensiometer.

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