Laboratory and greenhouse studies were undertaken to determine the usefulness of K Quantity, Intensity and Capacity factors in evaluating K supply capacities and in predicting K uptake by maize in 14 representative soils of South Western Nigeria. The results showed that the activity ratio was a poor index of the available K and was incapable of correct prediction of K uptake during prolonged cropping. The potential Buffet Capacity was higher in the soils on basement complex than in soils derived from sedimentary origin, indicating that depletion of K on cropping will be faster in soils derived from sedimentary rocks than those on the basement complex. The results also showed that the fixed K Quantity factor and the Potential Buffer Capacity could provide useful information in characterising the differential Buffer behaviour of soils.