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The Influence of Anions on Potassium Quantity-Intensity Relationships¹

ABSTRACT

Quantity-intensity (Q/I) relationships for potassium (K⁺) of soils sampled from three Maury silt loam sites (fine-silty, mixed, mesic, Typic Paleudalfs) representing different crop management practices were investigated in 10^–2 mol_c L^- each of Cl^- or SO^2-₄ solutions. Soil samples from the three sites were (i) low in exchangeable K⁺ and organic matter (LK-LOM), (ii) high in exchangeable K⁺ with low organic matter (HK-LOM), and (iii) high in exchangeable K⁺ with relatively high organic matter (HK-HOM). A theoretical evaluation of K⁺ Q/I plots in Cl^- or SO^2-₄ solutions employing the Gapon equation, revealed that the potential buffering capacity for K⁺ (APBC^k), the labile K⁺ (AExK⁰) and equilibrium activity ratio for K⁺ (AR^K0) based on single ion activities and ion pairs of CaSO⁰₄, KSO^-₄ and CaCl⁺ were independent of the type of solution anion. When considering total dissolved concentration of K⁺ and Ca²⁺, the potential buffering capacity for K⁺ (CPBC^K) and equilibrium concentration ratio for K⁺ (CR^K0) differed between Cl^- and SO^2-₄ solutions. The labile K⁺ (CExK⁰) remained the same. These results were due to the differences in ion pairing abilities between Cl^- and SO^2-₄ with K⁺ and Ca²⁺. The influences of the ion pairs are minimized at decreasing CR^K0 values. The experimental data describing Q/I relationships for K⁺ for the three soil samples were not in full agreement with the theoretical observations. The data showed that the type of anion (Cl^- or SO^2-₄) had an effect on the CR^K0 and CExK⁰, but the values were not significantly different except for the HK-HOM sample. The experimental data for the soil samples HK-LOM and HK-HOM indicated agreement to some extent with the theoretical evaluation. For the same CR^K values in the Cl^- or SO^2-₄ anions, a greater change in exchangeable K⁺ (ExK) was observed in the SO^2-₄ system than in the Cl^- system. However, for these two soil samples (HK-LOM and HK-HOM) when the Q/I plots were constructed considering single ion activities, differences remained in the Q/I plot components AR^K0 and AExK⁰ between the two anionic systems. For the LK-LOM soil sample the Q/I plots appeared to be nearly identical for the Cl^- and SO^2-₄ systems in terms of total cation solution concentrations and/or solution single ion activities. This agreed with the theoretical evaluation.

¹ Contribution from the Dep. of Agronomy, Univ. of Kentucky, Agric. Exp. Stn., Lexington, KY. The investigation reported in this paper (no. 85-3-157) is in connection with a project of the Kentucky Agric. Exp. Stn. and is published with the approval of the director.

² Associate Professor, Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091.

Received for publication August 12, 1985.

This article has been cited by other articles:

				V. P. Evangelou and J. Lumbanraja Ammonium-Potassium-Calcium Exchange on Vermiculite and Hydroxy-aluminum Vermiculite Soil Sci. Soc. Am. J., March 1, 2002; 66(2): 445 - 455. [Abstract] [Full Text] [PDF]