Species factor and evapotranspiration for an Ash (Fraxinus rotundifolia) and Cypress (Cupressus arizonica) in an arid region

The determination of crop coefficients (species factor) and evapotranspiration are important for estimating irrigation water requirements in order to have better irrigation scheduling and water management. The aim of this study was to determine the species factor and evapotranspiration for a reference crop of grass (Lolium perenne) and for two typical landscape crops of Ash (Fraxinus rotundifolia) and Cypress (Cupressus arizonica) using field drainage lysimeters in an arid region of Isfahan in central part of Iran. The potential evapotranspiration was estimated using nine different common methods. Among these methods, the FAO-Radiation, Turc-Radiation-Grass and FAO-Blaney-Criddle methods showed very close agreement with the lysimeter data. The Penman-Monteith 56 and FAO-Corrected-Penman methods showed moderate agreement with the lysimeter data. The Hargreaves, Priestley-Taylor, Makkink 1957 and Penman-Kimberley did not show close agreement with the lysimeter data. The adjustment factors were suggested to overlap the estimated values to the lysimetric values. The values of the species factor for Ash for four different growth stages (first-stage, crop-development, reproductive stage and late-season) were 0.24, 0.56, 0.73 and 0.37, respectively. The values of the species factor for Cypress for the above four different growth stages were 0.32, 0.44, 0.58 and 0.34.