Estimation of natural amounts of soil cations from strontium equilibration

Chemical extraction of soil plant nutrients may change the soil solution and the solid phase concentrations that are expected to occur under field conditions. The objective of this paper was to develop a mathematical procedure to calculate natural concentrations of major soil cations and potassium (K) diffusion parameters likely to occur under field conditions. Analytical information from strontium (Sr) equilibration and a water extract to determine the electrical conductivity were used in the derivation. The cation exchange reactions were described with Gapon's equation. Two basic assumptions were used in the derivations: 1) the selectivity coefficients between cations in the Sr equilibration system and in the natural soil system are equal; 2) the ratios of cations of the same charge in the natural system are equal to the ratios in the Sr equilibration system. Mathematical expressions to calculate concentrations and activities of major soil cations, assumed to be independent of the extraction procedure, were obtained after several iterations. Equations to express K diffusion parameters expected to occur under natural field conditions are proposed