Water resource planners use a water-production function, which is the relationship between yield and evapotranspiration (E) to determine the economic impact of various water allocation decisions. Wheat and barley were irrigated with a range of water levels using a sprinklerline-source to determine yield and evapotranspiration under deficit irrigation.

The water-production functions for spring and winter barley were different and varied under different levels of fertilizer. However, expressing the data in terms of relative yield and relative evapotranspiration produced a common water production function. The grain water-production functions for the winter wheat under nonnitrogen stress conditions were the same over years. The average wheat water-production function at Clovis, New Mexico, was statistically different from a derived wheat water-production function in Yuma, Arizona. However, when the water-production functions were again expressed in relative yield and relative E terms, the production functions became statistically the same (P < 0.05) and transferable to either site. The transferability of a water-production function from Location to location can be accomplished, when expressed in relative terms, under varying climate conditions and varying fertilizer levels. Water stress also affects the physiological development rate and physiological characteristics of both barley and wheat. The changes in the physiological characteristics of the crops can be used to estimate the resulting decrease in yield caused by moisture stress.