ABSTRACT

Fast-fruiting cotton cultivars are subject to late season potassium (K) deficiencies, and research indicates that foliar applications of low K rates partially corrects the deficiency. This research was initiated in 1991 to evaluate soil and foliar applied K to soils varying in Mehlich I extractable K. Research was conducted at the Milan, Jackson and Ames Plantation experiment stations on a Loring silt loam, and Lexington silt loam and a Memphis silt loam, respectively. The Mehlich I extractable K levels were high for the Loring and Lexington soils and low for the Memphis soil. Both conventional (CT) and no-tillage (NT) production systems were utilized at each site. The experimental design was a split plot arrangement of a randomized complete block with treatments replicated five tines. Main plot treatments were 0, 30, 60, and 120 lb/A K₂O 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. A foliar N application of Ca(NO₃)₂ equal to the N rate applied in of the KNO₃ foliar treatment was applied to separate the N and K 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 K application for both tillage systems. On the Loring soil, NT yields were increased with K20 rates up to 60 lb/A. Yields were not affected by soil K applications on the CT high K testing soils or the NT high K testing Lexington soil. 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 slightly from the foliar N applications. Petiole K concentrations were not affected by foliar applications on any soil or tillage system. The data suggests that foliar K applications are not effective for increasing CT yields on soil having high extractable K levels.