Five studies were conducted in California's San Joaquin Valley in 1990 and 1991 to evaluate the response of cotton to foliar applied N and K. The soils where the tests were conducted had a history of cotton showing K deficiency symptoms in late August or early September. One location had a low exchangeable soil K (85 ppm), while other sites were adequately high (approx. 200 ppm) .

Three of the tests were small hand sprayed plots (two rows, 50 feet long). In two tests, materials were applied by a tractor sprayer and plots were eight rows wide by the length of the field.

In tests which compared KNO₃ with KCl, cotton sprayed with KNO₃ resulted in highest yields, but not always significantly higher. Other forms of N and K such as Balance (1-18-18), Growmore (5-10-40 and 6-30-30), and Actival (5-0-17), gave variable results.

Applying K in the first irrigation resulted in a significant increase in lint yield when combined with foliar applications of N and K. Water run KCl also significantly increased petiole levels of K. When interactions of water run K treatments and sampling dates were contrasted, there were significant differences in petiole N, P, and K.