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 requires previous edaphic regionalization to estimate the potential acidity. The objectives of this study were to evaluate the soil-water-buffer ratio more adapted to soils from the homogeneous micro-region of Brejo Paraibano and to establish an equation to estimate the potential acidity of these soils by determination of the equilibrium pH of the soil suspension with the SMP solution. One hundred and twenty representative soils samples of the region were analyzed by the conventional calcium acetate method. Also determined was the pH SMP in the equilibrium suspensions soil-water-buffer 10:10:5, 10:20:10 and 10:25:5. The results have demonstrated that the best correlation between H + Al values and pH SMP was obtained with the 10:10:5 suspension and that the equation y = 164.31 - 47.26 x + 3.4717 x², expressing H + Al (y) values in cmol c dm², can be used to estimate H + Al values of the studied soils.
soil reaction; potential acidity; buffer solution
