Soil- and Foliar-Applied Potassium in Upland Cotton (Gossypium hirsutum L.) Production

Abstract

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 (67.3, 100.9, 134.5, 168.1, 201.8, 235.4, and 269.0 kg K2O ha-1) were organized in a randomized complete block design. Foliar K treatments were added to create a split-plot design. Foliar treatments were applied at 4.5 kg K2O ha-1 at the beginning of flowering, and again 10 days later. Results from E.V. Smith Research Center in 2018 indicated 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. At E.V. Smith 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, Alabama Cooperative Extension System’s soil-test K recommendations were correct for K fertilization recommendations for optimum crop yield. At Headland, cotton yield was unaffected by either soil or foliar K, likely a result of K located below typical soil test depths. Over 2 locations and 2 years there was little evidence that soil K in excess of current recommendations increased yields, nor that foliar K increased yield.