Effects of Temporally Variable Deficit Irrigation Management on Yield and Water Use in Early-Maturing Cotton.

Water deficit stress can limit cotton growth and cause reduction in lint yield and quality. Cotton plants require optimum moisture during some critical periods, however not all the physiological growth stages are equally sensitive to water stress. Current plans for deficit irrigation in cotton are mostly consistent over time and/or the severity of the stress levels. The optimal deficit irrigation plan would likely have an irrigation rate scheme which is temporally variable. Providing a sufficient level of water during the critical stages and withholding water at other stages to prime the plants for stress would more likely result the best results. To investigate this issue we established a greenhouse experiment where four different water regimes were tested for an early maturing cotton variety (Phytogen 222) in 17 L pots. The volumes of water for all the treatments were determined prior to each watering event based on the percent water use in well-watered control treatment. The four treatments were: 1) well-watered, 2) a. 25% weeks 1 – 2, b. 50% weeks 3 – 6, c. 100% weeks 7 – 14, and, d. 50% week 15 – harvest. 3) a. 25% weeks 1 – 2, b. 50% weeks 3 – 6, c. 75% weeks 7 – 14, and, d. 50% week 15 – harvest. 4) a. 25% weeks 1 – 2, and, 50% weeks 3 – harvest. The pots were weighed and watered every 3 days. Chlorophyll and stomatal conductance measurements were taken at the end of each watering schedule. Growth characteristics such as plant height, leaf, squares, and node numbers were also recorded at the same times. At the conclusion of the study, cotton lint yield, seed yield and fiber quality will be determined and the most ideal watering regime will be identified among the tested management plans.