Cotton (Gossypium hirsutum L.) and potassium (K) dynamics are not well understood particularly in soils with high K levels. Potassium is important for cotton reproductive development as it influences the number, size, and weight of bolls and can improve fiber quality by mitigating moisture stress. In the case that soil cannot replenish solution K from exchangeable reserves to meet the plant demands, deficiencies may occur leading to decreased yield (lint and seed) and fiber quality, reduced drought and disease tolerance, and premature boll opening. Studies were conducted in 2016 and 2017 in Lubbock (Olton clay loam and Acuff loam) and Lamesa (Amarillo fine sandy loam), TX, to determine the effects of K application rates and timing on lint yield and fiber quality of modern cotton cultivars (DP 1518 B2XF, DP 1522 B2XF, DP 1321 B2XF, and DP 1612 B2XF). Pre-plant soil tests were >250 mg K kg–1 at both locations and years at the 0-to-15-cm soil depths. Potassium treatments were applied at 0 (control), 90, and 180 kg K ha–1 as pre-plant, side-dress, or split applications. Harvest results determined that pre-plant and side-dress K applications produced significantly greater lint yield only for DP 1518 B2XF at both locations, while effects on fiber quality varied by location. The response of DP 1518 B2XF to K fertilizer was due to greater K use efficiency and possibly K demand of this cultivar compared to the others. This research provides evidence for continued investigation of cultivar by environment-based K management.