Calculations performed using a Gapon-type exchange equation agreed with experimental observations of the influence of lime on solution potassium levels in a soil with a high pH-dependent cation exchange capacity (CEC). As lime additions increase the pH and the CEC, solution potassium decreases. Amounts of potassium that must be added to the soil to reach solution pK-1/2p(Ca + Mg) = 2 were calculated to increase from 84 parts per 2 million at no lime to 1150 parts per 2 million for the high-lime level. The influence of lime on potassium availability could be even more severe if not for the decrease in potassium selectivity relative to calcium with increasing charge density.