Submitted to: Irrigation Associations Exposition and Technical Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2007
Publication Date: 12/9/2007
Citation: Piccinni, G., Ko, J., Wentz, A., Leskovar, D., Marek, T., Howell, T.A. 2007. Determination of crop coefficients (Kc) for irrigation management of crops. In: Proceedings of the 28th Annual International Irrigation Show, December 9-11, 2007, San Diego, California. p. 706-719. 2007 CDROM. Interpretive Summary: Water use from corn, spinach, onion, cotton, and wheat was measured with monolithic weighing lysimeters at Uvalde, Texas over a five year period. Water use from a cool-season grass (tall fescue) was also measured with another monolithic weighing lysimeter to determine the grass reference evapotranspiration, ETo. The crop coefficient, Kc, was determined as the ratio of the measured crop water use, Etc, to Eto [Kc = Etc/ETo]. Two to three years of data for each crop were averaged for the Kc data. Peak Kc values were 1.2, 1.05, 0.85, 1.25, 1.23 for corn, spinach, onion, cotton, and wheat, respectively. These Kc data will improve irrigation scheduling and water management in the Texas Winter Garden and South Texas. The data are important to producers and regional water districts.
Technical Abstract: Weighing lysimeters are used to measure crop water use during the growing season. By relating the water use of a specific crop to a well-watered reference crop such as grass, crop coefficients (Kc) can be developed to assist in predicting crop needs using meteorological data available from weather stations. Seven lysimeters, consisting of undisturbed 1.5 x 2.0 x 2.2 m deep soil monoliths, comprise the Texas Agricultural Experiment Station - Uvalde lysimeter facility. Six lysimeters, weighing about 14 Mg, have been placed each in the middle of a one hectare field beneath a linear LEPA irrigation system. A seventh lysimeter was established to measure reference grass ETo. Corn, sorghum, spinach, onion, cotton, and wheat were grown over the last five years in the lysimeter fields. Daily water use was measured on 5-min intervals. Crop water requirements, Kc determination, and comparison to existing FAO Kc values were determined over a 2 or 3 year period depending on the crop.