Evapotranspiration (ETc), or crop water use is the water removed from the soil by evaporation from the soil surface and transpiration by the plant. Evaporation can account for 20–30% of growing season ETc for corn. Transpiration is the last step in a continuous water pathway from the soil, into the plant roots, through the plant stems to leaf surfaces and into the atmosphere. Approximately 70–80% of crop water use is resulted from plant transpiration. The amount of daily corn water use varies with atmospheric conditions: air temperature, humidity, solar radiation and wind speed. Higher ETc caused by high air temperatures, low humidity, clear skies and high wind speed, but lower ETc will result from high humidity, clear skies and low wind speed (Kranz et al., 2008).