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This article in SSSAJ

  1. Vol. 45 No. 4, p. 749-753
    Received: Nov 26, 1980
    Accepted: Apr 5, 1981

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Sodium-Calcium Exchange in Nile Delta Soils: Single Values for Vanselow and Gaines-Thomas Selectivity Coefficients1

  1. Tarek H. Sheta2,
  2. George R. Gobran2,
  3. Joseph E. Dufey3 and
  4. Henri Laudelout3



Na-Ca exchange measurements were carried out on 11 representative soils from the Nile Delta. Experiments were conducted over a wide range of exchanger compositions. Due to their common alluvial origin, all soils showed identical exchange properties.

The experimental data appeared to be well described either by a single Vanselow selectivity coefficient or by a single Gaines-Thomas coefficient. The Gapon coefficient, as originally defined, increased linearly with the exchangeable calcium fraction (or decreased with ESP). After examining the sensitivity of those coefficients to experimental errors, as a function of the exchanger composition, values of 5.97 and 2.30 mol/liter were calculated for the Gaines-Thomas and Vanselow coefficients, respectively. These correspond to a Gapon coefficient as redefined by Sposito equal to 48 (mol/m3)½.

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