Nine K‐rich soils belonging to three Orders often found in Southern Italy (Inceptisol, Alfisol, Vertisol) were extracted with H2O, CaCl2, NH4OAc, HCl, Mehlich, HNO3reagents for K and the results were compared to the EUF method. Significant correlations between the reagent extracted K and EUF K were found. The results allowed us to distinguish three basic K fractions: (i) actually available, (ii) quickly released reserve and (iii) slowly released reserve. The EUF provided both quantitative and qualitative data, suitable for a “dynamic” diagnosis of K soil fertility saving time and reagents. The EUF curves showed an unexpected strong K affinity for Inceptisol, the soil which was richest in K.