The use of electrochemical attributes has been suggested by a number of authors to characterize the colloidal soil compound and to serve as evaluation indices of certain properties related to plant fertility and nutrition and to pedogenesis, underlying regional soil differentiation. In this study, the relations between the point of null saline effect (PESN) and chemical properties of three Oxisols of a toposequence in the microbasin Chico Nunes, Mato Grosso were evaluated. Surface and subsurface samples were submitted to chemical, mineralogical and electrochemical characterization. The organic carbon, inversely, and the oxalate-Al oxides, directly, explained almost the entire variation of the PESN in the studied soils. The PESN values determined by means of potentiometric titration were well correlated with the values of point of zero charge (PCZ), calculated from pH values measured in KCl 1 mol L-1 solution (pH KCl) and in water (pH H2O) by means of the equation PCZ = pH KCl - pH H2O, reinforcing its usefulness in estimating PESN values of tropical soils with variable charge. Likewise, the index DpH = pH KCl - pH H2O) was highly correlated with difference PESN - pH H2O, proving the applicability of this index in the estimate of the signal and the magnitude of the surface liquid charge of highly weathered soils.
Cerrado soils; double diffuse layer; surface electric charge
