Water requirements of olive orchards - II: determination of crop coefficients for irrigation scheduling

Intensification of olive cultivation by shifting a tree crop that was traditionally rain fed to irrigated conditions, calls for improved knowledge of tree water requirements as an input for precise irrigation scheduling. Because olive is an evergreen tree crop grown in areas of substantial rainfall, the estimation of crop evapotranspiration (ET) of orchards that vary widely in canopy cover, should be preferably partitioned into its evaporation and transpiration components. A simple, functional method to estimate olive ET using crop coefficients (K-c=ET/ET0) based on a minimum of parameters is preferred for practical purposes. We developed functional relationships for calculating the crop coefficient, K-c, for a given month of the year in any type of olive orchard, and thus its water requirements once the reference ET (ET0) is known. The method calculates the monthly K-c as the sum of four components: tree transpiration (K-p), direct evaporation of the water intercepted by the canopy (K-pd), evaporation from the soil (K-s1) and evaporation from the areas wetted by the emitters (K-s2). The expression used to calculate K (p) requires knowledge of tree density and canopy volume. Other parameters needed for the calculation of the K-c's include the ET0, the fraction of the soil surface wetted by the emitters and irrigation interval. The functional equations for K-p, K-pd, K-s1 and K-s2 were fitted to mean monthly values obtained by averaging 20-year outputs of the daily time step model of Testi et al. (this issue), that was used to simulate 124 different orchard scenarios.