Research in Evapotranspiration: Energy Sources for Evapotranspiration in the Plains Region

摘要

Evapotranspiration studies at the University of Nebraska, 1966-1969 are summarized. A six acre field was equipped for irrigation. Two precision weighing lysimeters and meteorological instrumentation were installed. Maximum summer evaporative flux was found to be about equivalent to an energy consumption of 1.2 cal/sq cm/min. Nocturnal evaporation accounted for about 10% of the total evaporation from bare soil. The Bowen-ratio energy balance method gave good agreement with measured evapotranspiration from alfalfa. Climatological methods were also studied for predicting potential evapotranspiration. Greenhouse and field trials of antitranspirant effectiveness on alfalfa were conducted; several materials reduced transpiration in the greenhouse, but in field trials, variability in soil water content and soil characteristics obscured differences caused by treatment. An analytical model predicts that antitranspirants will, in the eastern Great Plains climate, be largely ineffectual. The tools available provide opportunities for measurement of potential evapotranspiration for continued testing of the Bowen-ratio energy balance method, and for development of climatological methods for estimating long term water use on a regional basis. (WRSIC abstract)