4979. Oasis effect : Vertical energy transfer from air to the crop; effect of dry fallow surrounds on the microclimate of a relatively small acreage of land where an air mass moving into an irrigated area will give up much sensible heat. For small fields this may result in a higher ET (crop) as compared to predicted ET (crop) using climatic data collected inside the irrigated area; conversely ET (crop) predictions based on weather data collected outside the irrigated fields may over-predict actual evapotranspiration losses.