Effect of irrigation termination times on cotton cultivars with contrasting maturities

Optimizing irrigation termination time can save water and preserve lint yield and fiber quality in cotton. Although there is currently an irrigation termination recommendation in Georgia, the ideal time for termination could be influenced by cultivar differences in maturity. The hypotheses of this study were that differential irrigation termination times will affect lint yield, fiber quality, and incidence of hardlock and boll rot, and responses will be dependent on cultivar differences in maturity. In 2021 and 2022, a study was conducted in Camilla, GA, using two cotton cultivars with contrasting maturities under four irrigation termination treatments. Irrigation was terminated at cutout, first open boll, 2 weeks after first open boll, and 4 weeks after first open boll. Measurements included plant growth, cutout date, lint yield, irrigation water use efficiency (IWUE), fiber quality, and incidence of boll diseases. Gas exchange measurements and percent open boll estimates at each irrigation termination time were also conducted. Terminating irrigation at cutout did not significantly affect yield in either year; however, IWUE increased 12.6% relative to current recommendations and 13.2% relative to the latest termination time in the 2022 season. Cultivars differed significantly in cutout date, agronomic maturity, gas exchange rates, yield, hardlock/boll rot incidence, and fiber quality. However, there was no interaction between cultivar and irrigation termination time for any parameter. We conclude that irrigation can be terminated at cutout to maximize IWUE, for early and late-maturing cultivars, without limiting yield or fiber quality, assuming a water-replete soil profile at termination. Defining early irrigation termination times that do not penalize yield in cotton can increase water use efficiency.Terminating irrigation at cutout maximized water use efficiency in an early and a late maturing cultivar.Cultivar affected yield, fiber quality, water use efficiency, and disease incidence.