The quantity-intensity (Q/I) approach was applied to evaluate the effects of liming on K equilibria in four major agricultural soils of Rio Grande do Sul, Brazil. The amount of labile K estimated from the Q/I parameters ΔK° and Kc, decreased slightly with liming. However, the most pronounced changes in Q/I parameters following liming were an increase in the buffering capacity (BCk) and a decrease in the intensity factor (ARko). Double layer theory and effects of liming on exchangeable Al and polynuclear Al-OH complexes were used to partially explain these effects. It is apparent from this study that liming these soils leads to relatively lower amounts of K in solution at equivalent exchangeable levels. This results in lower leachability of native or added K, but it might also contribute to K deficiencies for crops if the intensity factor were lowered below the critical level.