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This article in SSSAJ

  1. Vol. 57 No. 5, p. 1241-1246
    Received: June 3, 1992

    * Corresponding author(s):


Organic Matter Role in Illitic Soil Colloids Flocculation: I. Counter Ions and pH

  1. Dean Heil  and
  2. Garrison Sposito
  1. Dep. of Agronomy and Horticulture, New Mexico State Univ., Las Cruces, NM 88003
    Dep. of Soil Science, Univ. of California, Berkeley, CA 94720



Dispersed soil particles have a negative impact on soil structure and contribute to soil erosion and contaminant movement. The colloidal properties of soil clays have been found to be different from specimen clays. The purpose of this study was to investigate the effect of organic matter on the flocculation of soil colloids as a function of electrolyte concentration, pH, and exchangeable or soluble bivalent cation type. The flocculation of suspensions of two illitic soils was studied using light transmission. Soil suspensions were prepared in Na-K-Ca and Na-K-Mg perchlorate solutions at a total electrolyte charge concentration of 5, 10, and 15 molc m−3 at pH 6 and 8. Flocculation at a given soluble bivalent cation charge fraction was increased as the organic C content of the soil colloids decreased. Calcium was more effective than Mg as a flocculant at the same soluble or exchangeable bivalent cation charge fraction. Increasing pH caused an increase in the flocculation of one of the soils, but this trend was reversed after the removal of organic matter by H2O2 treatment. The amount of electrolyte required for flocculation, the effect of pH, and the relative effectiveness of Ca vs. Mg all depended on soil organic matter content.

Contribution from the Dep. of Soil Science, Univ. of California, Berkeley. This research was supported by the Kearney Foundation of Soil Science.

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