The aim of this work was to assay a method for CEC determination at the soi
l pH to be applied to acid soils. Argentine agricultural ultisols and molis
ols soils were used for this purpose. CEC with 1M NH4Ac pH 7 and CEC with 1
M NH4Ac and NH4Cl, at the soil pH, were determined. Values of CEC determine
d with both electrolites at the soil pH were significant lower (p < 0.05) t
han the values obtained with NH4Ac at pH 7 and these differences were highe
r for the ultisol soils.