Crop water use and stage-specific crop coefficients for irrigated cotton in the mid-south, United States.

Regional variations in environmental conditions, cultivars, and management practices necessitate locally derived tools for crop water use estimation and irrigation scheduling. A study was conducted in northeast Louisiana (mid-south US) aimed at estimating daily crop evapotranspiration (ET c ) and reference evapotranspiration (ET o ) and thus, developing local crop coefficient ( K c ) curves for irrigated upland cotton. ET c was determined using paired weighing lysimeters installed near the middle of a 1-ha cotton field and planted with cotton as in the rest of the surrounding field, while ET o was calculated using the Standardized Reference Evapotranspiration Equation (SREE) developed by the American Society of Civil Engineers (ASCE), using estimates of weather variables from a nearby standard reference weather station. Stage-specific K c values averaged over 2 years were 0.42, 1.25 and 0.70 for initial, midseason, and end season stages of cotton, respectively. The initial-stage K c value was approximately 26% lower than the Food and Agricultural Organization (FAO)-adjusted initial K c value. The mid- and end-season K c values obtained in the study were approximately 6% and 11% greater, respectively, than the FAO-adjusted K c values for the corresponding stages. The observed differences among the local stage-specific K c values (especially at initial growth stage of cotton) and the FAO-adjusted initial K c values could be attributed to regional variations in environmental conditions, cultivars, and management practices. The ET c and K c values obtained from this study provide research-based information for future studies and the development of K c -based irrigation tools in this region. [ABSTRACT FROM AUTHOR]