Crop Coefficients (Kc) are crop specific evapotranspiration values generated by research used with reference evapotranspiration data to estimate the crop’s evapotranspiration requirement (ETc). ETc is calculated by multiplying the crop coefficient (Kc) by the reference evapotranspiration value (ETo).
For more information about Crop Coefficient
http://www.fao.org/docrep/X0490E/x0490e0b.htm
http://biomet.ucdavis.edu/evapotranspiration/CropCoef/crop_coefficients.htm - from UC Davis Biometeorology
Comments about crop coefficients for Hass Avocado on Mexican Seedling Rootstocks - James Oster and Mary Lu Arpaia