2,500 gallons per bushel

Tom Trout can't really see underground. But he employs the superpowers of field research to peer under the surface and to see how much water crop roots are absorbing. His aim, he says, is to measure "crop water productivity function."

Rather than measure water-use efficiency by calculating crop yield per drop of water applied, Trout has turned that approach on its head and is determining potential yield per drop of water absorbed. So runoff (or leaching) is deducted from the total water applied, leaving only the moisture absorbed by the crop.

To determine moisture-absorption rates, the USDA Agricultural Research Service (ARS) engineer is leading a team of researchers into a fifth year of fieldwork involving corn, wheat, sunflowers, and pinto beans being grown on a 50-acre farm outside of Greeley, Colorado. The crops receive six rates of irrigation – from full irrigation down to only 40% of full.

Trout and his colleagues, Walter Bausch, Dale Shaner, and Lori Wiles, designed the research to determine the level of limited irrigation that is economically best for those four crops. This information will provide more accurate guidance on irrigation amounts and timing.

High-crop platform elevates sensors
The effort has lead the team to create some rather unique research tools. Soil-moisture sensors and a water station (both common features in irrigated fields these days) were at work. But the team fashioned a high-crop platform to roll down rows carrying a telescoping boom across the top of the crop being evaluated. That platform is equipped with digital cameras, infrared detectors, and an infrared thermometer all suspended 15 feet above the crop from a telescoping boom. The platform is at work weekly, rolling across fields monitoring crop growth and also leaf temperature, an indicator of water deprivation.

Regenesis Management Group of Denver, Colorado, is working with the ARS team to create monitoring instruments and software for a Web-based application being designed by the company, known as SWIIM (Sustainable Water and Innovative Irrigation Management).

Research discoveries
In the first three years of research, each acre of land in the study produced about 10 bushels of corn for each inch of water consumed. That equates to 1 pound of corn for each 60 gallons of water absorbed.

Trout found that corn yields varied from 210 bushels for a full application of water down to 130 bushels for the lowest irrigation level.

On a per-acre basis, Trout found an acre of corn consumes about 600,000 gallons of water to produce 200 bushels of corn. "After an initial amount of water to get the corn growing, the consumption rate stayed about the same through all six levels of irrigation – about 2,500 gallons per bushel of corn," Trout says.

This flies in the face of the traditional belief that crops use water less efficiently as they get more of it. But in this research, Trout discovered that while that is true in terms of drops of irrigation water applied, it is not necessarily true in terms of drops of water consumed. In other words, there is no reduction in the amount of water corn takes in to produce each bushel, despite the reduction in the amount of irrigation water applied. This may make limited irrigation less attractive financially, at least for corn in this region.

"Corn farmers might do better financially to use full irrigation on a portion of their irrigated acres, rather than limited irrigation spread over all the acres," Trout says. "They could then sell or lease the water rights on the nonirrigated acres (a practice that is common along the eastern range of Colorado). Another option would be to grow a different crop that requires less water, if the economics of limited irrigation work for that crop."

Learn more

Tom Trout | 970/492-7419 | thomas.trout@ars.usda.gov