Due to the minimal cation exchange capacity of sandy soils and limited K fertilization, K deficiency may be an important factor affecting bermudagrass production and persistence in Florida. The objectives of this study were to evaluate effects of N and K fertilization levels on Jiggs bermudagrass productivity and storage organ mass and to determine critical levels of tissue K concentration. The experiment was conducted in a greenhouse in Ona, FL from August to December 2014. Treatments were the factorial combinations of N (0, 50, and 100 kg N ha-1
) and K fertilization levels (0, 20, 40, and 80 kg K2
) after every harvest, distributed in a completely randomized design with four replicates. The “E” horizon of a Pomona sand soil was collected and used as growing medium in tree seedling pots (10 cm diameter x 41 cm height), with approximately 10 kg of soil per pot. Plants were harvested at 15-cm stubble height every 6 wk, and root and rhizome mass determined at the end of the experiment. There were no effects of K fertilization levels on herbage accumulation (HA) and root and rhizome mass when no N was applied; however, at 50 and 100 kg N ha-1
both response variables increased linearly with increasing K fertilization. There was a quadratic relationship of HA with tissue K concentration, and HA increased as tissue K increased up to 17 g K kg-1
DM (critical level). Potassium content in roots and rhizomes decreased linearly with increasing levels of N fertilization when K fertilization was 0 or 20 kg K2
. Conversely, K content in root and rhizome increased with increasing levels of N fertilization when 80 kg K2
was applied. Nitrogen and K2
O fertilization should be supplied at similar levels to sustain production and persistence of bermudagrass hayfields in Florida.