Fast-fruiting cotton cultivars are subject to late season potassium (K) deficiencies, and research indicates that foliar applying low K rates partially corrects the deficiency. This research was initiated in 1991 and continued through 1993 evaluating soil and foliar applied K to soils of varying Mehlich I extractable K. Conventional- (CT) and no-tillage (NT) production were evaluated on a Loring, Lexington, and Memphis silt loam soils. Mehlich I extractable K levels were high for the Loring and Lexington soils and low for the Memphis soil. The experimental design was a split plot arrangement of a randomized complete block with treatments replicated five times. Main plot treatments were 0, 30, 60, and 120 lb/A K₂O broadcast rates and sub-plot treatments were foliar applications of K and nitrogen (N). Potassium nitrate was foliar applied at 4.4 lb/A K₂O four times during the growing season on a two week interval. Applications were initiated 2 weeks after early bloom on the Loring and Lexington soils but at early bloom on the Memphis soil. Calcium nitrate was foliar applied at a N rate equal to the KNO₃ foliar treatment to evaluate N and K effects on yields. A total of 80 lb/A N using ammonium nitrate and 40 lb/A P₂O₅ using triple superphosphate was broadcast on all plots prior to planting. Muriate of potash (KCl) was broadcast on the main plots prior to planting. The cultivar DPL 50 was planted in 40 inch rows during the first week of May. Petioles were collected from the first mature leaf from the top of the plants prior to each foliar application.

Soil-applied K increased CT and NT yields on the low K testing Memphis soil and NT yields on the high K testing Loring soil. Yields on the Memphis soil were increased with each rate of soil-applied K for both tillage systems. On the Loring soil, NT yields were increased with soil K₂O up to 60 lb/A. Yields on either CT high K testing soils or the NT high K testing Lexington soil were unaffected by soil K applications. Petiole K concentrations were increased by soil-applied K on the Memphis soil for both tillage systems. Foliar K applications increased CT and NT yields on the Memphis soil and the NT yields on the Loring and Lexington soils. The NT yields on the high K soils were increased by the combination of both foliar N and K application. Petiole K concentrations were not affected by foliar applications to the CT and NT Lexington or CT Memphis soils. However, petiole K was increased for the CT and NT Loring and NT Memphis sites. The data suggests that foliar K applications are effective for increasing cotton yields on high extractable K NT soils and on both CT and NT yield on low K soils.