Foliar feeding of cotton: Evaluating potassium sources, potassium solutionbuffering, and boron

Foliar applications of K may be used to supplement soil applications to max imize yields of cotton (Gossypium hirsutum L.). Response to foliar Ii appli cations 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 (coar se-silty, mixed, acid, thermic Aquic Udifluvents) and on a Memphis silt loa m (fine-silty, mixed, active, thermic Typic Hapludalfs) to evaluate KNO3, K 2SO4, K2S2O3, and KCl as K sources. A second study evaluated foliar KNO3 an d K2SO4 solutions applied unbuffered and buffered to pH 6 and 4 on cotton K nutrition and yield. Foliar Ii in both studies was applied at 4.1 kg K ha( -1) per application. A third study evaluated combinations of soil-applied a nd foliar-applied B and K. Foliar treatments were applied in 93.5 L ha(-1) water at early flower or 2 ak after and repeated on a 9- to 14-d interval b etween the four applications. Yields from the four Ii sources averaged 10% higher than the untreated check and yields with KNO3 were 4% higher than th e 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 surfactan t (ethoxylated alkyl aryl phosphate esters) to KNO3 resulted in 5% higher y ields 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 0.1 1 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 buffer ing and/or the inclusion of foliar B are relatively inexpensive ways of imp roving yield response. Based on yield increases in this study, these treatm ents should return 8 to 10 times the product rests.