Selectivity, fixation, and exchange equilibria of potassium in six Tennessee soils and soil fractions

Selected physical, chemical, and mineralogical properties were listed for reference samples from the soils from which the samples studied were obtained. Investigations were conducted to compare properties of the samples used to the properties given for the reference samples. Six soils were used in the studies and each soil was separated into five fractions on the basis of particle size. Calcium and potassium exchange capacities were determined for all soils and soil fractions. The calcium was determined by chemical means and the potassium by the use of radioactive potassium. Calcium exchangeable potassium and the additional ammonium exchangeable potassium were determined for all soils and soil fractions. Selectivity coefficients for the replacement of calcium by potassium on the soils were determined by the leaching column method. Potassium plus calcium solutions having a total concentration of 0.002N with three ratios of calcium to potassium were used. Free energies, standard heats and entropies for the exchange of calcium by potassium on the soils were evaluated at two temperatures. Selectivity coefficients for the replacement of calcium by potassium on the soils and soil fractions were determined using radioactive potassium-42 traced potassium plus calcium solutions. The solutions used had a total concentration of 0.002N and three ratios of calcium to potassium. A solution having a total concentration of 0.02N was employed, but only one ratio of calcium to potassium was used at this concentration. The potassium "fixed" against extraction by calcium was measured on part of the soils and soil fractions after determination of the selectivity coefficients. The Iberia sand fraction was found to possess an unusually high cation exchange capacity. It was noted that most of the material in this sand fraction was concretionary. Investigations were made to determine the nature of this material. Presence of a pH dependent charge was studied, and x-ray diffractograms, specific gravity determinations, a partial elemental analysis, and an x-ray spectral analysis were run in the investigations. Photographs of the material were obtained through a microscope and features shown in the photographs were discussed.