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Present research was undertaken to understand the effect of long-term potassium (K) fertilization @ 0 kg (K 0 ) and 80 kg (K 80 ) K ha −1 on the quantity/intensity (Q/I) parameters for K in soil and characterize the Aeric Haplaquept soil for K supplying capacity under long-term continuous rice cropping. The study involved laboratory experiments on Q/I parameters of the soils in different depths (0–75 cm depth) from long-term K management experimental field. The Q/I parameters showed a linear relationship for both K omission and K fertilized soils at different depths. Omission of K decreased the equilibrium K concentration ratio (CR 0 K ) compared to K applied to the soil and slightly decreased the labile K (K L ) and non-specifically available K (-ΔK 0 ) but had no effect on specifically available K (K X ). The K omission increased the potential buffering capacity (PBC K ) compared to K fertilized soil. Potassium management had little effect on equilibrium exchangeable K (EK 0 ), magnitude of the conversion of added K to exchangeable pool (α) and non-exchangeable pool (β). However, equilibrium solution K (CK 0 ) in K omission soil was lower than K applied soil. β was higher than α in both the K management conditions. The PBC K for non-exchangeable pool was also higher than exchangeable pool both in K omission and K fertilized soils. Potassium management influenced critical solution K (CKr) and critical exchangeable K (EKr) but had no effect on minimum exchangeable K (Emin). Since the exchangeable K (EK), EKr and EK 0 is very close to Emin it is concluded that EKr and Emin should be consider in interpreting the K fertility specially the EK of soil under long-term wetland double rice cultivation. [ABSTRACT FROM AUTHOR]