where KS is a stress reduction coeffcicnt [0 - 1], and KC is a soil water evaporation
coefficient. The Kcb represents the ratio of ETC to ETo under conditions when the soil surface layer is dry, but where the average soil water content of the root zone is adequate to sustain full plant transpiration. KS reduces the value, for Kcb when the average soil water content in the root zone is not adequate to sustain full plant transpiration. K. represents evaporation from wet soil that is in addition to ET represented in Kcb. The stun Kcb + Ke can not exceed the maximum value for a crop.