Exchange Equilibria of Potassiumin Soils: Effect of Clay Mineralogy of Soilson K-Ca Exchange

Exchange behaviour of potassium versus calcium in relation to clay mineralogy of eleven soil samples from different locations in India and the erst while Federal Republic of Germany was investigated. The experimental results were analyzed using the Q/I parameters, thermodynamic approach and empirical selectivity coefficients. The equilibrium activity ratio of potassium (AR_o) for different soils ranged between 0.11 and 17.7 (mol^0.5 L^−0.5) x 103, and potential buffering capacity at AR_o (PBCo) between 8.4 and 7695 cmol kg⁻¹ L^0.5 mol^−0.5. The Gapon and Vanselow selectivity coefficients (K_G and K_V at the minimum and the maximum experzmental K-saturatlon ranged from 4.5 to 53.5 and 0.6 to 3 L^0.5 and 81 to 11332 and 0.4 to 6.2 L mol⁻¹, respectively. The standard free energy of K-Ca exchangefor different soils ranged between -1.08 and-7.02 kJ mol⁻¹. The relative decrease in K-preference with increased K-saturation was steeper in soil from Germany. The parameter PBC: CEC give better indication of K-preference of soils than PBC_o. TItt value of mean PBC for 0 to 10% K-saturation were considerably smaller than those of PBC_o.