Soil and Foliar-Applied Potassium Fertilizers in Upland Cotton Production

Soil test recommendations for upland cotton (Gossypium hirsutum L.) fertility are often based on varieties which are no longer in production, meriting questions on whether increased potassium (K) is needed for new varieties with higher yield potential. Additional K can be applied as soil-applied or foliar-applied K. However, recent studies have produced inconclusive data regarding the efficacy of foliar potassium applications in upland cotton.  The objective of this work was to evaluate K uptake by cotton (Deltapine 1646 B2XF) as a function of foliar and soil-applied K. Field studies were established at Auburn University’s E.V. Smith Research Center (Shorter, AL) and Wiregrass Research and Extension Center (Headland, AL). Four replicate treatments of soil-applied K (67, 101, 134, 168, 202, 235, and 269 kg K₂O ha^-1) were organized in randomized complete bock design.  Foliar K treatments were added to create a split-plot design. The foliar treatments were applied at 5.4 kg K₂O ha^-1 at the beginning of flowering, and again 10-14 days later.  Results from E.V. Smith Research Center in 2018 indicate that foliar K did not have a significant effect on cotton lint yield. Cotton yield increased with added soil-applied K, up to 67.3 kg K₂O ha^-1.  Initial soil-test K was 105.4 kg K ha-1 (a ‘medium’ soil-test level), with a K fertilization recommendation of 44.8 kg K₂O ha^-1.  Thus, in this single-year, one site experiment soil-test K recommendations were correct for K fertilization recommendations for best crop yield.