Scheduling Irrigation Using Predawn Leaf Water Potential Increases Water Use Efficiency in Cotton

Traditionally, the timing and amount of water applied to a crop has been scheduled based on balancing water lost to transpiration with rainfall amounts. Although this method consistently results in high crop yields, there is the potential to decrease irrigation amounts, while maintaining high yield, using plant-based indicators of water deficit to trigger irrigation. Direct indicators of plant water status, such as leaf water potential have been used to schedule irrigation in some tree crops; however research on cotton is sparse. Indirect measures, such as canopy temperature have been applied to many crops; however, this method has not been widely adopted in the southeastern United States due to physiological limitations imposed by the typically humid climate.  To this end, cotton grown in Southern Georgia over two years was irrigated according to the University of Georgia’s checkbook recommendation, as well as by three distinct irrigation thresholds based on ΨPD (-0.5, -0.7, -0.9 MPa).  To evaluate the use of indirect indicators of plant water status, canopy temperature was monitored throughout the growing season for use in modifying the crop water stress index (CWSI).