A study of cation exchange in South African soils

Abstract

The colloidal fraction is the vital part of a soil. These extremely minute particles determine the nature of the soil and are mainly responsible for its many and varied functions. The most important of these functions is perhaps the ability of the colloids to adsorb and exchange cations, the elements so essential to all organisms as building materials. When pure water is passed through a non-saline. soil, the leachate will contain very few dissolved cations. If, on the other hand, an electrolyte such as a weak solution of sodiun chloride, is passed through the same soil, the leachate will contain considerable quantities of calcium, magnesium and potassiun chlorides as well as much of the original sodium chloride. The number of equivalents of the cations collected will be approximately the same as the number of equivalents of sodium ions added. Sodium ions have displaced some of the calcian, magnesium and potassium ions from the soil. This phenomenon is known as cation exchange. Intro., p. 1.