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Soil Science Society of America Journal Abstract -

Organic and Inorganic Anion Effects on Reference and Soil Clay Critical Flocculation Concentration


This article in SSSAJ

  1. Vol. 56 No. 6, p. 1762-1766
    Received: Sept 26, 1990

    * Corresponding author(s):
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  1. H. Frenkel,
  2. G. J. Levy  and
  3. M. V. Fey
  1. Institute of Soils and Water, The Volcani Centre, P.O. Box 6, Bet Dagan, Israel
    Dep. of Agronomy, Univ. of Natal, P.O. Box 375, Pietermaritzburg 3200, Republic of South Africa



Maintaining adequate soil permeability and favorable soil structure is largely dependent on the flocculation-dispersion characteristics of the soil clay fraction. The critical flocculation concentration (CFC) of the clay fraction of three strongly structured clay soils from Natal (two dominated by smectite and one by kaolinite) was compared with that of smectite (bentonite from Wyoming) and kaolinite (from Georgia) in Na- and Ca-saturated forms. The soil clays had much higher CFC than their reference mineral counterparts in both NaCl and CaCl2 systems. The addition of humic acid extracted from one of the soils and of citrate, formate, orthophosphate, carbonate, and silicate to the reference clays increased the CFC by as much as a factor of 50. Kaolinite was approximately 10 times more sensitive than bentonite to this dispersion effect of specifically adsorbing ligands. The results suggest that natural levels of soil humus, and possibly of certain inorganic anions, may be sufficient to impart a high degree of dispersion on the soil clay fraction. There is, therefore, some doubt as to the quantitative importance of clay mineral composition in the dispersion behavior of soils.

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