عنوان مقاله [English]
Although climate change in most parts of the world has changed the amount of water consumed in agriculture, various data from FAO are still used in irrigation planning and in determining allocation of irrigation water. The aim of this study was to determine the accuracy of FAO global data for sugar beet crop coefficient in Ardabil plain. At first, parameters of the water balance equation including rainfall and irrigation, drained water, soil water storage, and sugar beet evapotranspiration were determined, using three volumetric lysimeters. After preparation of lysimeters, on May 2017, sugar beet was planted in the lysimeters and the surrounding area, and irrigated. Volumes of drainage water collected from the lysimeters after each irrigation and volumetric water content before each irrigation was measured. Finally, using the measured data, the water balance equation was completed for various time intervals and the plant evapotranspiration and crop coefficients were determined for different quadruple growth stages. Means comparison was performed using t student test at two probability levels of 1% and 5%. Results showed that total the seasonal evapotranspiration of sugar beet plant was 1013 mm. The average crop coefficients for the first, second, third, and the fourth growth stages and the whole growing period were 0.33, 0.9, 1.16, 0.88, and 0.9, respectively. At two probability levels of 1% and 5% and in all growth stages, the mean of measured crop coefficient values was not significantly different compared to the values provided by FAO. The measured crop coefficient values are in good agreement with the published FAO values, therefore, the published data by FAO can be used for irrigation scheduling in the studied area.