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This article in SSSAJ

  1. Vol. 25 No. 6, p. 456-459
    Received: Jan 16, 1961
    Accepted: Jan 24, 1961

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Psychrometric Measurements of Soil Samples Equilibrated on Pressure Membranes1

  1. L. A. Richards and
  2. Gen Ogata2



The osmotic pressure or solute suction (SS) of the extract from a “saturated” soil paste can be measured with a thermoelectric psychrometer which is calibrated by use of standard osmotic solutions. The same psychrometric procedure can be used to measure the total soil-moisture stress or total suction (TS) of water in soil that has been equilibrated with a pressure membrane at known soil-moisture tension or matric suction (MS). From membranous and psychrometric measurements, the difference ΔS = TS - (MS + SS) was evaluated for 134 samples of Pachappa soil at three SS levels (0.3, 2.5, and 5 bar) attained by leaching with calcium chloride solutions and three MS levels (5, 10, and 15 bar). Mean ΔS values at 5, 10, and 15 bar MS were, respectively, −0.6, −0.4, and −0.1 bar. Mean ΔS values at 0.3, 2.5, and 5 bar SS were, respectively, −1.0, +0.04, and +0.5 bar. Standard deviation values for MS, SS, and TS, respectively, were 0.07, 0.1, and 0.5 bar.

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