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This article in AJ

  1. Vol. 68 No. 6, p. 995-996
    Received: Mar 8, 1976

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Extended Field Use of Screen-Covered Thermocouple Psychrometers1

  1. Ray W. Brown and
  2. Robert S. Johnston2



The use of screen-covered thermocouple psychrometers for in situ measurements of soil water potential has been criticized because of possible soil and micro-organism contamination through the screen covering. Double-junction Peltier psychrometers with a screen covering were installed in the soil under field conditions for periods ranging from 2 to 40 months of continuous exposure, and were then removed and examined for evidence of loss of calibration sensitivity and contamination by soil particles and micro-organisms. The uncleaned psychrometers were recalibrated in the laboratory and then disassembled and examined under a microscope (250 ✕) for contamination. Although slightly more than half of the units lost some sensitivity after field exposure, the average decrease was less than 5%. The psychrometer cavities were all nearly free of soil particles, the thermocouple junctions were shiny, and no evidence of microbial attack was evident. It appears that long-term field exposure of screen-covered psychrometers is no more detrimental to their performance than that of ceramic or other psychrometers.

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