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Foliar Feeding of Cotton: Evaluating Potassium Sources, Potassium Solution Buffering, and Boron

Plant and Soil Sci. Dep., West Tennessee Exp. Stn., 605 Airways Blvd., Jackson, TN 38301

Carl E. Sams

Plant and Soil Sci. Dep., Univ. of Tennessee, P.O. Box 1071, Knoxville, TN 37901

^* Corresponding author (wtes2{at}aeneas.net).

Foliar applications of K may be used to supplement soil applications to maximize yields of cotton (Gossypium hirsutum L.). Response to foliar K applications may be improved by choice of K source, buffering the spray solution, or applying K with B. Research was conducted on a Collins silt loam (coarse-silty, mixed, acid, thermic Aquic Udifluvents) and on a Memphis silt loam (fine-silty, mixed, active, thermic Typic Hapludalfs) to evaluate KNO₃, K₂SO₄ K₂S₂O₃, and KCl as K sources. A second study evaluated foliar KNO₃ and K₂SO₄ solutions applied unbuffered and buffered to pH 6 and 4 on cotton K nutrition and yield. Foliar K in both studies was applied at 4.1 kg K ha^–1 per application. A third study evaluated combinations of soil-applied and foliar-applied B and K. Foliar treatments were applied in 93.5 L ha^–1 water at early flower or 2 wk after and repeated on a 9- to 14-d interval between the four applications. Yields from the four K sources averaged 10% higher than the untreated check and yields with KNO₃ were 4% higher than the other K sources. Buffering two K source solutions to pH 4 resulted in 10% higher yields than the check or unbuffered K solutions. Adding a surfactant (ethoxylated alkyl aryl phosphate esters) to KNO₃ resulted in 5% higher yields then the check. Compared with untreated check yields, soil-applied B at 0.56 kg B ha^–1 increased yields by 6%, four foliar applications of 0.11 kg B ha^–1 increased yields by 8%, and four foliar applications of 0.11 kg B plus 4.1 kg K ha^–1 increased yields by 13%. Foliar K solution buffering and/or the inclusion of foliar B are relatively inexpensive ways of improving yield response. Based on yield increases in this study, these treatments should return 8 to 10 times the product costs.

Received for publication May 18, 1997.