Crop water use (transpiration) during the growing season is a major factor in attaining high yield potential. Soil water loss (evaporation) and crop water loss (transpiration) occur simultaneously; making predictions of evapotranspiration complex. Actual evapotranspiration values vary greatly from day to day (0.04 to 0.40 inches/day) because of the following factors:

• Soil: residue cover, soil texture, soil moisture in the profile
• Crop: crop type, growth stage, cultivar
• Climate: radiation, temperature, relative humidity, wind speed