Rapid-maturing, short-season cotton varieties present a strong demand on plant available potassium (K), especially during fruit maturation. Enhanced maturity of the cotton plant, and improvement in certain fiber properties and lint yields due to K fertilizers have been reported. Cotton response to K usually occurs in soils rated low to medium in soil test K. This study was conducted to determine the need for supplemental K fertilization of cotton grown on a typical South Texas soil testing adequate to high in available K. Soil and foliarly-applied KNO3 fertilizer was compared with soil-applied KCl. Combinations of preplant (PP) and sidedress (SD) applications were studied. Treatments were arranged in a randomized block design with four replications. Results of the three-year study show variable crop response to K treatment. In all years, cotton failed to respond to foliarly-applied KNO3 or soil-applied KCl. However, soil-applied KNO3 at 20 lb Ac(-1 )increased lint yields significantly (116 lb Ac-1) in 1992 (first year treatment) and showed an 81 lb Ac-1 yield increase in 1993. Increase in boll size and boll numbers reflected the lint increase. Of the four fiber properties studied, only fiber strength appeared to be consistently improved by soil-applied KNO3. Cotton petiole analyses showed some increase in K concentration due to K treatment but the effects were not consistent.