The use of the pH SMP to estimate the potential acidity has advantages in relation to the 0.5 mol L-1, pH 7, calcium acetate method, but it requires previous edaphic regionalization to estimate the H + Al values with safety. In the northwestern region of the State of Paraná there are soils originally developed from sandy sedimentary rock of the Caiuá Formation, called Caiuá Sandstone, of the Cretaceous period. These soils are characterized by low contents of clay and organic matter, and a low buffer capacity, differing from most of the other soils in the state. The objective of this research was to compare the pH SMP and the 0.5 mol L-1, pH 7 calcium acetate methods, in order to establish an equation to estimate the potential acidity of soils in this area, by determination of the equilibrium pH of the soil suspension with the SMP solution. One hundred and fifty soil samples of this area were submitted to regression analyses, evaluating three regression models according to the estimate quality, by statistics of their coefficients and behavior of their residues (measured-estimated). The linear equation H + Al = 20.1925 - 2.6484 pH SMP (R² = 0.9051) estimated the potential acidity of Caiuá Formation soils best.
buffer capacity; sandy soils; soil chemistry; cation exchange capacity; soil pH
