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United States Department of Agriculture

Agricultural Research Service

Title: Evapotranspiration

Authors
item Hatfield, Jerry
item Prueger, John

Submitted to: Encyclopedia of Agricultural, Food, and Biological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 20, 2001
Publication Date: August 26, 2003
Citation: HATFIELD, J.L., PRUEGER, J.H. EVAPOTRANSPIRATION. ENCYCLOPEDIA OF AGRICULTURAL AND FOOD ENGINEERING. 2003. P. 278-281.

Technical Abstract: Evaporation of water is a critical environment process. Evaporation is the physical process of converting liquid water into vapor and the release of large amounts of energy during this conversion process. The cooling that results from the energy released during evaporation benefits, animals, humans, and plants. This benefit includes maintaining temperatures within critical limits for optimum physiological function. The application of the evaporation process to plants and plant communities has some added dimensions compared to animals or humans. Plants have roots that extend into the soil and extract water from deeper regions of the soil profile. This water is transported through the vascular tissue contained in roots, stems, and leaves and is released to the atmosphere through stomata. These stomata serve as the sites for the evaporation process to occur within the leaf with water moving through the stomata into the atmosphere. This special process of evaporation from plants is referred to as transpiration. Evapotranspiration is affected by four primary factors: the amount of energy available, the gradient of water vapor between the surface and atmosphere, the rate of transport of water vapor mass from the surface to atmosphere (windspeed gradient), and the amount of soil water stored in the soil profile. Understanding evapotranspiration amounts is critical for crop decisions and soil management.

Last Modified: 4/23/2014
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