Application of K Q/I concept for K availability assessment constitutes a rational approach for K fertilizer management. The K Q/I isotherm was used to determine K availability in soils of contrasting landscape positions in the humid rainforest, southeastern, Nigeria. Also K forms and soil properties were determined using standard methods. Equally, K forms and Q/I parameters obtained were inter-correlated and also correlated between each other and with soil properties using correlation analysis. Soil K decreased in the order total (1.03) > non-exchangeable (0.46) > mineral/lattice (0.24) > available (0.17) > exchangeable (0.12) > water soluble K (0.04cmol Kg-1) with most significantly (P < 0.05) correlated amongst each other and with most soil properties. Also, mean equilibrium K, Ca, K, ±∆K and AReK ranged from 5.27-12.23, 2.40-6.03, 1.69-4.05, 2.77-9.72 cmol kg-1 and 2.85-3.06 mol L-1)-1/2 respectively, with values increased with added solution K. Equally, mean K Q/I parameters ranged from 2.45-3.85 mol L-1/2 x 10-3 (ARe OK), 3.08-4.00 cmol kg-1(Ko), 3.25–5.80 cmol kg-1 (Kx), 6.75-9.38 cmol kg-1 (KL) 1.99-3.61 cmol kg-1 mol L-1)1/2 (PBC OK), 6.89-11.12 cmol kg-1 (Kp), 0.19-0.34 mol L-1)1/2 and -2268.89- -2017.87 cal mol-1(∆G) and differed significantly (LSD 0.05) amongst most soil depths and landscape positions. Furthermore, soils were not K deficient and with availability seriously influenced by K Q/I parameters, K forms and soil properties. Finally, available K of the soil was specifically held on wedge or edge sites of clay minerals with the soils not likely for immediate K fertilization.