Diurnal evapotranspiration measurements were made over lowbush blueberries and potatoes in Maine during selected portions of the 1977 and 1978 growing seasons. Half hourly measurements were made using a Bowen ratio-energy budget method. Data from these measurements provided the principal energy budget components, an evaluation of potential evapotranspiration, and an array of diagnostic measures used to evaluate the partitioning of available energy into sensible and latent heat. Evapotranspiration rarely reached potential values and a large variability was found to exist. In an attempt to provide a reliable daily estimate of evapotranspiration from potatoes, using a minimum number of environmental measurements, the equilibrium evaporation equation of Priestly and Taylor was examined. A modified version of this equation, incorporating a soil moisture tension term to account for drying soil conditions, was established to predict daily evapotranspiration rates.https://digitalcommons.library.umaine.edu/aes_techbulletin/1104/thumbnail.jp