Evaluation of ET-HS model for estimating water demand and water use efficiency of sugar beet in semi-arid condition of Isfahan, Iran

Hargraves-Samani method is one of the methods for calculating plant evapotranspiration that needs minimum meteorological data. In order to evaluate ET-HS model in determining sugar beet crop water demand in Isfahan, an experiment was conducted at research field of Department of Agriculture, Khorasgan Branch, Islamic Azad University, Isfahan, Iran in 2005. The study was based a Randomized Complete Block Design with three replications and six irrigation treatments. Irrigation treatments included irrigation to supply 50, 75, 100, 125 and 150% of crop water demand on the basis of ET-HS model and control on the basis of 90 mm evaporation from Class A evaporation pan during growing season. Results showed that the effect of irrigation treatment was significant on total dry matter and root yield. In addition, root yield increased in the treatment of irrigation to supply 150% of crop water demand. But, sugar percentage increased up to irrigation to supply 100% of crop water demand albeit insignificantly, and then started to decrease. White sugar yield significantly increased to 8.7 t.ha-1 up to irrigation to supply 100% of crop water demand and then, started to decrease with further increase in irrigation level. The highest water use efficiency for root yield was obtained from the irrigation to supply 50% of crop water demand. Given the precision of ET-HS model in control treatment, it can be used for irrigating sugar beet in such regions as Isfahan and sugar beet water demand can be determined only on the basis of the daily temperature data without using the data of evapotranspiration or soil water depletion, so that the yield does not decrease and the appropriate white sugar yield is obtained by the application of minimum irrigation level.