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This article in SSSAJ

  1. Vol. 39 No. 3, p. 552-555
    Received: June 10, 1974
    Accepted: Feb 10, 1975

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Potassium-Calcium Equilibria in Sandy Soils Containing Interstratified Micaceous Clay1

  1. A. S. P. Murthy,
  2. J. B. Dixon and
  3. G. W. Kunze2



Neutral to alkaline soils from several climatic and physiographic locations were studied. The clay mineralogy of these soils was characterized by interstratified mixtures of mica, montmorillonite and little vermiculite. X-ray diffraction patterns for the most abundant clay fraction, < 0.2 µm, were composed of weak diffuse reflections for mica-expansible components when they were Mg-saturated and glycolated. Sand and silt fractions contained K-feldspar and mica as possible sources of K+.

The two most micaceous soils produced Q/I curves with a horizontal range indicating further K+ sorption ceased in spite of the increased K+/Ca2+ ratio. The amount of K+ in the labile pool determined by the Q/I method was correlated best with the amounts of mica in the whole soil (r2 = 0.89) suggesting that mica in coarse and fine fractions acted as a potential source of labile K+ in these soils. A multiple regression equation was developed that predicted the amount of K+ in the labile pool from the amounts of mica and feldspar in the soil (R2 = 0.96). The results of this study suggest that mica in these soils will contribute K+ to the labile pool. The multiple regression coefficient indicated that feldspar content was negatively related to labile K+.

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