Quantity – intensity (Q/I) isotherms were used to evaluate the dynamics of potassium in eight soil samples of Ismailia Governorate, Egypt. The results showed that the potassium activity ratio (AR_e^k) values for all soils increased as the K⁺ concentration of the equilibrating solutions increased. El Qantara West soil had the highest AR_e^k value (12.0 (mole l^-1)^0.5 × 10^-3) while Eltal Elkebier soil had the lowest value (3.20 (mole l^-1)^0.5 × 10^-3). El Qantara West soil had the highest labile K value (0.56 cmole Kg^-1 soil), while the Eltal Elkebier soil had the lowest labile K value (0.10 cmole Kg^-1), and the exchangeable K in this sample was higher than the labile K. The results showed that the potassium potential buffering capacity (PBC^k)values of the investigated soils ranged between 23.1 and 46.7 (cmole Kg^-1) / (mole l^-1)^0.5. Free energy (-ΔG) values ranged between 4.36 - 5.70 Kcal mole^-1. In addition, the results showed that the Gapon selectivity coefficient (K_G) varied between 3.81 and 51.9. The exchangeable K and -ΔK_e^o had a positive correlation coefficient (r = 0.70). AR_e^K values were highly correlated with logarithmic values (pK- 0.5pCa+Mg) obtained from equilibration of a single sample (r = -0.87). The potential buffering capacities were highly correlated with the exchangeable K (r = 0.83). Q/I parameters were influenced by soil properties and K forms. It could be used to sustained K fertilizer management in order to rationalize and increase fertilizer use efficiency (FUE).