The gradual depletion of the Ogallala Aquifer in the Southern High Plains of Texas has resulted in reduced well capacities for cotton (Gossypium spp.) irrigation. This study investigated cotton cultivar responses to reduced irrigation from flowering to harvest (2013); and then evaluated season long water deficits and the impact of the timing and amount of irrigation (2014). In 2013, field-grown cotton irrigated with 5 mm per day irrigation showed relatively low stress levels as exemplified by efficiency of quantum yield values between 0.17 and 0.23. Reducing irrigation levels from 5 mm per day to 2.5 mm per day at flowering produced a range of stress levels of Fv/Fm from 0.28 to 0.54. In 2014, four of the commercial cultivars were grown in replicated plots receiving either 2.5 mm of irrigation per day or 17.5 mm of irrigation once a week. Cultivar differences in plant stress were detected for the daily and weekly irrigation strategies. Changes in plant size, boll production, and timing of cutout were observed. FM 2484B2F and Phytogen 72 exhibited no yield differences between the irrigation regimes, while All-Tex Edge and Phytogen 367 showed yield decreases (20% and 25%) under the 2.5 mm daily irrigation regime. Alteration of the timing for the limited irrigation can impact existing stress sensitivities by reducing stress levels and increasing yields.
