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This experiment in cotton from cv. DPL-50 was held at the Tidewater Agricultural Research and Extension Center, Virginia, USA, in a thick free soil for 3 years. The effect of foliar applications of K on the cotton yield in the experiment was investigated. Foliar sprays were applied every two to three weeks or starting weekly from the first flowering. The source of K was KNO₃ for foliar treatments and KCl was applied to the soil with a recommended dose of 56 kg K₂O / ha. KNO₃ was sprayed at 2.24; 4,48 and 6,72 kg / ha with a hand held carbon dioxide spray at a rate of 15.3 L / ha. Although foliar treatments at intervals of two to three weeks did not significantly increase yield, a slight increase was observed. The KNO₃ applied foliarly at intervals of five to seven days generated a significant increase in the yield of the fiber in comparison with the untreated plots. A 20% increase in fiber yield (196 kg / ha) was observed. The highest fiber yield is associated with the combination in the application of K to soil and foliar, which indicates the importance for the plant of having K available during the development of the cotton acorn. As explained by the author, the doses of KNO₃ applied were lower than in the previous trials with potassium nitrate applied foliarly at a dose of 11,2 kg / ha. This may explain the lack of consistent response to foliar treatments in this trial.