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

Abstract

Regional variations in environmental conditions, cultivars, and management practices necessitate locallyderived tools for crop water use estimation and irrigation scheduling. A study was conducted in northeastLouisiana (mid-south US) aimed at estimating daily crop evapotranspiration (ETc) and reference evapo-transpiration (ETo) and thus, developing local crop coefficient (Kc) curves for irrigated upland cotton. ETcwas determined using paired weighing lysimeters installed near the middle of a 1-ha cotton field andplanted with cotton as in the rest of the surrounding field, while ETowas calculated using the Standard-ized 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 Kcvalues averaged over 2 years were 0.42, 1.25 and 0.70 for initial, midseason, and end seasonstages of cotton, respectively. The initial-stage Kcvalue was approximately 26% lower than the Food andAgricultural Organization (FAO)-adjusted initial Kcvalue. The mid- and end-season Kcvalues obtained inthe study were approximately 6% and 11% greater, respectively, than the FAO-adjusted Kcvalues for thecorresponding stages. The observed differences among the local stage-specific Kcvalues (especially atinitial growth stage of cotton) and the FAO-adjusted initial Kcvalues could be attributed to regional vari-ations in environmental conditions, cultivars, and management practices. The ETcand Kcvalues obtainedfrom this study provide research-based information for future studies and the development of Kc-basedirrigation tools in this region.