| Abstrakt: |
Ion exchange equilibria have been investigated in mineral soils, but little information is available for organic soils. This investigation was undertaken to characterize the cation selectivity of differing histosols and to determine a suitable cation exchange equation to express the ion selectivity in these soils. Four histosols were incubated for 3 weeks with 5 levels of K and Rb. At the end of incubation, ions in soil solution and on the adsorbed phase were determined. All soils had a greater fraction of Ca in the exchange phase than in solution, whereas with Mg, Na, K, and Rb, the reverse occurred. Increasing K and Rb saturation was related to an increase in kRb/K. On the Pahokee muck soils, Rb was adsorbed more tightly than K, where the amount of Rb added exceeded 1.0me/100g of soil. On the Edwards muck soil, Rb was adsorbed preferentially to K at all levels. Magnesium was adsorbed preferentially to Ca on the Edwards muck soil, but not on the Pahokee soils. Selectivity coefficients for K-Ca were calculated using the Kerr, Gapon, Krishnamoorthy and Overstreet, Vanselow, and Scheffer and Ulrich equations. In all but the Scheffer and Ulrich equation, the selectivity coefficient decreased as K and Rb were increased. In the latter it increased. No equation satisfactorily described the system. |
