Crop Water Use (Evapotranspiration)

atmometersThe evapotranspiration (ET) process is a key variable in many disciplines including,

  • irrigation management,
  • crop growth,
  • hydrologic cycle,
  • plant physiology,
  • soil-plant-water-atmosphere relationships,
  • microclimate and surface interactions, and
  • drainage studies.

ET can be defined in a broad definition as the combined process of both evaporation from soil and plant surfaces and transpiration from plant canopies through the stomates to the atmosphere.

In the ET process, water is transferred from the soil and plant surfaces into the atmosphere in the form of water vapor.

Crop ET can be measured directly using advanced techniques. However, in practice, the most commonly used method of estimating the ET rate for a specific crop requires first calculating reference ET and then applying the proper crop coefficients to estimate actual crop ET.

The first publication below provides a brief description of the evapotranspiration process and its role in the hydrologic cycle. It provides detailed information on the reference and actual evapotranspiration and crop coefficient concepts.

ET gagesThe second publication presents detailed information on one of the tools (ETgages) to measure reference evapotranspiration and provides guidelines and examples as to how to calculate actual crop evapotranspiration for a specific crop from the ETgage data and crop coefficients.

Evapotranspiration Publications from UNL 

Ecological Systems: Origin of Evapotranspiration (PDF 8pgs, 389KB)
Author: Suat Irmak. This article was originally published in the Encyclopedia of Ecology, Volumes 1-5 published by Elsevier.

Using Modified Atmometers (ETgage®) for Irrigation Management
This NebGuide describes the atmometer (evapotranspiration gauge) and explains how it can be used for irrigation scheduling. Examples are provided to show how information collected with an atmometer can be used to estimate crop water use for corn and soybean.
PDF version (4 pgs, 975 KB)

For more on ET, ETgage and irrigation scheduling, please visit the Nebraska Agricultural Water Management Network pages, and the Agricultural Irrigation: Management pages.