Editorial to the special issue on “Contributions to update the FAO56 guidelines for computing crop water requirements”

The editorial of the current Special Issue (SI) describes and comments the twelve papers included in it. First, the questions relative to update the FAO56 guidelines on crop evapotranspiration are discussed with explaining why the papers of the SI focus on the crop coefficients (K_c) and their consistent importance of after more than half a century of use. Then, papers relative to tabulated K_c for orchards, grass crops and natural vegetation are presented and, following, various field studies determining crop evapotranspiration for deriving K_c and K_cb values are discussed.