Potassium-Calcium Equilibria in Sandy Soils Containing Interstratified Micaceous Clay1
- A. S. P. Murthy,
- J. B. Dixon and
- 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+.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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