Determination of Actual Evapotranspiration and Crop Coefficients of California Date Palms Using the Residual of Energy Balance Approach

As water scarcity becomes of greater concern in arid and semi-arid regions due to altered weather patterns, greater and more accurate knowledge regarding evapotranspiration of crops produced in these areas is of increased significance to better manage limited water resources. This study aimed at determining the actual evapotranspiration (ETa) and crop coefficients (K-a) in California date palms. The residual of energy balance method using a combination of surface renewal and eddy covariance techniques was applied to measure ET(a)in six commercial mature date palm orchards (8-22 years old) over one year. The experimental orchards represent various soil types and conditions, irrigation management practices, canopy characteristics, and the most common date cultivars in the region. The results demonstrated considerable variability in date palm consumptive water use, both spatially and temporally. The cumulative ETa(CETa) across the six sites ranged from 1299 to 1501 mm with a mean daily ET(a)of 7.2 mm day(-1)in June-July and 1.0 mm day(-1)in December at the site with the highest crop water consumption. The mean monthly K(a)values varied between 0.63 (December) and 0.90 (June) in the non-salt-affected, sandy loam soil date palms with an average density of 120 plants ha(-1)and an average canopy cover and tree height of more than 80% and 11.0 m, respectively. However, the values ranged from 0.62 to 0.75 in a silty clay loam saline-sodic date palm orchard with 55% canopy cover, density of 148 plants ha(-1), and 7.3 m tree height. Inverse relationships were derived between the CET(a)and soil salinity (ECe) in the crop root zone; and between the mean annual K(a)and ECe. This information addresses the immediate needs of date growers for irrigation management in the region and enables them to more efficiently utilize water and to achieve full economic gains in a sustainable manner, especially as water resources become less available or more expensive.