ELECTROCHEMICAL PROPERTIES OF SOME ENTISO LS

Surface charge properties of three Entisols were studied by means of a cid-base potentiometric titrations, by direct measurement of ions adso rption and by determination of the DELTA pH (pH(KCl-pH(H20)) values. T he surface charge/pH curves obtained by acid-base potentiometric titra tions showed a well-defined pH value, where the variable surface charg e is zero (pH0). These pH0 values ranged from 7.8 to 8.8 for the three soils. Direct measurements of ions (K+ and NO3-) showed that pH and e lectrolyte concentration influence the magnitude of the electric charg es on the soil particles. Cation and anion retention measurements comb ined with the pH0 values showed the existence of a small amount of per manent negative charge, ranging from 1 to 3 mEq/100 g. The DELTA pH va lues also indicated the presence of a small amount of permanent negati ve charge and this charge would be associated with the clay content.