The K c coefficient serves as an aggregation of the physical and physiological differences between crops. Two calculation methods to derive crop evapotranspiration from ET o are presented. The first approach integrates the relationships between evapotranspiration of the crop and the reference surface into a single K c coefficient. The selection of the K c approach depends on the purpose of the calculation and the time step on which the calculations are to be executed. The final chapters present procedures that can be used to make adjustments to crop coefficients to account for deviations from standard conditions, such as water and salinity stress, low plant density, environmental factors and management practices.
Examples demonstrate the various calculation procedures throughout the publication.
Most of the computations, namely all those required for the reference evapotranspiration and the single crop coefficient approach, can be performed using a pocket calculator, calculation sheets and the numerous tables given in the publication. The user may also build computer algorithms, either using a spreadsheet or any programming language. These guidelines are intended to provide guidance to project managers, consultants, irrigation engineers, hydrologists, agronomists, meteorologists and students for the calculation of reference and crop evapotranspiration. They can be used for computing crop water requirements for both.