Abstract: the treatments without K application (12.15~12.81 vs 13.69~19.33 kJ/mol). There are significant correlations between the Q/I parameters and the 1 mol/L HNO3 extractable K, K+ saturation and soil organic matter. The Q/I parameters provide useful information for understanding the soil K status. Soil K supplying power is increased due to the long-term K fertilization, while, continuous cropping without K inputs could cause the remarkable depletion of available K especially in the fluvo-aquic soil and red soil. Quantity/intensity (Q/I) relationship of potassium (K) in soil was evaluated under a long-term K fertilization experiment. Soil samples collected from the NP and NPK treatments in the three soils (manural loess soil, fluvo-aquic soil and red soil) were analyzed for revealing the Q/I relationship of K, and the relationships between Q/I parameters and soil properties using Q/I approach under a 15 year wheat-corn cropping system. The values of K+ equilibrium activity ratio (AR0), soil labile K (KL), non-specific K (-△K0), and specific K (KX) in the NPK treatments are larger than those in the NP treatments. The AR0 and -△K0 values in the NPK treatments are 13.78 and 12.17 times larger than those in the NP treatments in red soil. The potential buffering capacity (PBC) is decreased (ranging from 17% to 20%) in the NPK treatments in manural loess soil and fluvo-aquic soil, and is not changed in red soil compared with those in the NP treatments. Free energies of K+ exchange for Ca2+ and Mg2+ (-△G) in the treatments with K fertilization are lower than those in the treatments without K application (12.15～12.81 vs 13.69～19.33 kJ/mol). There are significant correlations between the Q/I parameters and the 1 mol/L HNO3 extractable K, K+ saturation and soil organic matter. The Q/I parameters provide useful information for understanding the soil K status. Soil K supplying power is increased due to the long-term K fertilization, while, continuous cropping without K inputs could cause the remarkable depletion of available K especially in the fluvo-aquic soil and red soil.