Electrochemical Properties of Humid Tropical Soils

Abstract

Soil colloids of the humid tropics exhibit electrochemical properties which are characterized by colloids of constant surface potential type, whereas soils of temperate regions are characterized by colloids bearing a permanent surface charge model. Electrochemical charges of humid tropical soils. Naturally, are controlled by the pH, types of clay mineral, organic matter, and oxides of Fe and Al. So far, some of Thailand’s soils have been found to be of constant surface potential type. In general, the field soil pH values are higher than the pH at P.Z.C. (the point of zero charge or pH P.Z.C, and the pH P.Z.C.) values of top soils are lower than the pH P.Z.C. values of the same sub-soils. C.E.C. (cation exchange capacity) evaluation for soils, of which colloids are of constant surface potential type, as determined by ammonium acetate at pH 7 or barium saturation method at pH 8.2 gives an arbitrary value of C.E.C. and should be over estimated values.