Optimal K fertility management for cotton will require a basic understanding between soil test K levels and cotton K nutrition and yield. A previous three-year K fertilization experiment resulted in soil test K levels ranging from 210 to 520 lb K/acre in the 0 to 6 in. depth and 128 to 354 in the 6 to 12 in. depth. This provided an opportunity to evaluate varying soil test K levels on cotton yield, K nutrition, and incidence of verticillium wilt . The site was located south of Yazoo City, MS on a Morganfield silt soil (Coarse-silty, mixed, nonacid, thermic Typic Udifluvent). The experiment was arranged as a randomized complete block design involving four replications. The cotton variety used in this study was LA887. Leaf blade and petiole samples obtained at early bloom and whole plant samples taken at early boll opening were analyzed for K. Lint yield was determined by hand picking and ginning a 16.4 ft. length of row. Leaf blade and petiole K showed a significant relationship to soil test K in the 0 to 6 in. depth, but a stronger relationship was obtained for both parameters when soil test K in the 0 to 12 in. depth was considered. Total K uptake was influenced by soil test K, but the relationship suggested limited increases in K uptake beyond 500 lb/acre soil test K in the 0 to 12 in. depth. A quadratic relationship between soil test K (0 to 12 in.) and lint yield was obtained, but a low R² value of 0.31 suggests other factors were influencing yield. Incidence of verticillium wilt was reduced with increasing soil test K, suggesting that a buildup of soil test K can be use to minimize plant infection.