Potassium Rates for New Generation Cotton Cultivars.

Alabama cotton growers sometimes report that newer cotton cultivars use potassium differently than past cultivars.   A specific comment is that the new cultivars require more K than older cultivars, and they respond to higher rates of K, even if the soil test for a field indicates that soil K is adequate.  Thus, the objective of this project was to conduct a K rate x cultivar field study, examining the effect of K on cotton yield in various cultivars.  The experiment was conducted at the Plant Breeding Unit (PBU), located in Tallassee, AL.   The site was not irrigated, and had an initial soil test K of 141 kg K ha^-1, a ‘Medium’ soil test (recommended fertilizer K₂O application of 45 kg ha^-1).  Three cotton cultivars were used: Phytogen 499, Deltapine 1050 and Deltapine 491 (an older cultivar).  Potassium rates (as KCl) were 0, 34, 67, 100 and 134 kg K₂O ha^-1.  There were four replicates of each treatment for a total of 60 plots in the experiment (15 treatments).  Each plot was 4 rows wide (0.9 m row spacing) and 12 m long, with the middle two rows of each plot harvested.   All K was preplant broadcast applied and incorporated prior to planting.  Collected data included:  1) yield, 2) fiber quality, 3) date of first flower and first open boll, 4) plant height at first flower and first open boll, and, 5) tissue K (most recently emerged fully expanded leaves) at first flower and first open boll.  Only yield data is presented in this talk.  Plots were harvested on November 8^th, 2013. For seed cotton yield, there was not a significant cultivar x K rate interaction, which indicates that the different cultivars responded similarly to increasing potassium.  Phytogen 499 had a significantly higher yield than measured in Deltapine 1050 or Delta 491.  As K rate increased there was a significant linear increase in seed cotton.  There was not a different K response due to cultivar.