Potassium-Calcium Equilibria in Sandy Soils Containing Interstratified Micaceous Clay
1975
Murthy, A. S. P. | Dixon, J. B. | Kunze, G. W.
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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