The widespread occurrence of potassium (K) deficiency across the Cotton Belt has focused attention on the possible use of foliar fertilization with K. The objective of this three-year study was to investigate the effect of foliar-applied KNO₃, compared to soil-applied KCl, for alleviating K-deficiency and improving cotton (Gossypium hirsutum L.) yield and fiber quality. The study was conducted at 10 to 12 sites across the Cotton Belt. At all sites the recommended practices for high yield cotton production for that state were applied. Treatments consisted of (1) no added soil or foliar K, (2) low-soil-K as preplant KCl according to preplant soil tests, (3) high-soil-K preplant (double the recommended level in treatment 2), (4) low-soil-K-plus-foliar-K, and (5) high-soil-K-plus-foliar-K. The foliar rate was 10 lb KNO₃/acre applied four times at 10-14 day intervals after first flower.

Results were very variable and significant yield differences occurred about 40% of the time. The full data set will be summarized in a bulletin and conclusions drawn on a regional basis. While firm conclusions cannot be drawn at this time, foliar application of KNO₃ appears to offer some potential for supplementing preplant soil applications of potassium fertilizer, but the results are variable and somewhat unpredictable. It is clear that additional research is required to understand the physiological of plant K requirements and the soil buffering capacity.