Probing the Evapotranspiration Equation

Reducing agricultural soil evaporation through better irrigation and other practices would help save precious water.

To better study agricultural water loss, Suat Irmak, UNL soil and water resources engineer, has developed a network of advanced monitoring systems throughout Nebraska that continually measures evapotranspiration, the combined water lost to soil evaporation and through plant leaf surfaces.

"On a worldwide scale, 60 percent of the total precipitation goes back to the atmosphere by evapotranspiration," Irmak said. "In Midwestern states like Nebraska, it’s 90 percent. We have to measure evapotranspiration so we can have a good handle on what is happening to our water resources."

Irmak and his team travel the state to download data collected throughout the year by sophisticated equipment at 12 sites. The Nebraska Environmental Trust, Central Platte Natural Resources District, UNL Extension, the Nebraska Rural Initiative and others help fund this work.

These data enable Irmak to study how and when it’s possible to stress plants with less water without hurting yields. He also uses the information to research the effect of tillage, rotation, different crops and irrigation practices on evapotranspiration rates to develop water-saving management strategies.

In addition, farmers can use the real-time data to know how much to irrigate or adjust their practices to reduce water use. Appropriate irrigation, zero or reduced tillage and other management practices reduce evapotranspiration rates, making more water available for other uses, such as municipal water supplies and wildlife habitat.

Watershed managers and state policymakers can use accumulated data to better allocate water resources and develop effective water and agricultural policies.
 
Irmak’s evapotranspiration network is receiving attention from agriculturalists and the water resources community worldwide. "Evapotranspiration is critical for everything we do in water resources," he said. "We are one of the best institutions that has good quality resources in this research arena."