A field study conducted in North Alabama to evaluate cotton (Gossypium hirsutum) response to long-term applications of K fertilizer was sampled to evaluate the potential downward movement of applied K and the effects of applied K on the forms of soil K. The field test was initiated in the fall of 1986. Potassium was applied to a Dewey silt loam (Typic Paleudult) at rates of 0, 60, 120 and 180 lb K₂O acre^-1 for the first three years of the study. No K fertilizer was applied during the fourth year of the study (1990). After the fourth year of the test, half of the plots were left in residual. The experiment had a split plot design with four replications. During 1987-1989, two varieties were compared (Stoneville 825 and Deltapine 50) and these served as whole plots. During 1991-1997, only one variety was evaluated and annual versus residual K fertilization served as whole plots. Potassium treatments have been used as subplots throughout the test. Intensive soil sampling was conducted in the fall of 1989, 1993 and 1997. Analysis of soil samples collected at depths of 0-9, 9-15, 15-20, 20-25, and 25-30 inches showed that K fertilization increased the level of Mehlich 1, ammonium acetate and boiling nitric acid (nonexchangeable) extractable K in the surface 0-9 inch layer only. Ammonium acetate extracted higher amounts of K as compared to the Mehlich I extractant, but in 1994 both extracts gave similar correlation with lint yields. Quantity-Intensity (Q/I) relationships determined on surface samples collected in 1993 showed that the potential K buffer capacity of this Limestone Valley soil was not affected by the addition of K fertilizer. Exchangeable K determined using Q/I was lower as compared to ammonium acetate extractable K and was similar to values obtained using the Mehlich I extractant.