Yield per drop of water

High-crop sprayers have nothing on a one-of-a-kind mobile platform created by the ingenuity of USDA Agricultural Research Service (ARS) engineers in Greeley, Colorado. Besides being able to skim across cornfields at tassel height and taller, this vehicle packs its own telescoping crane.

While some farmers would love to get their hands on such a vehicle to service center pivots, the machine has proven invaluable in helping the team of Colorado ARS researchers pinpoint how much water it takes to grow a bushel of corn, wheat, sunflowers, or pinto beans.

This landmark research will assist farmers with increasingly limited water resources to determine how much yield they can produce in those four crops from each gallon of water applied.

The research team, consisting of USDA researchers Tim Trout, Walter Bausch, Dale Shaner, and Lori Wiles, has discovered that it takes 2,500 gallons of water to produce 1 bushel of corn.

The purpose of this precedent-setting research was to pinpoint the yield per drop of water that was actually consumed by the four crops. That measure is called a crop water productivity function, and it eliminates all water that does not enter a plant's roots.

High-tech high-boy

The high-boy platform innovated by the ARS team employs a raft of sensors to monitor crop growth and leaf temperature, which are indicators of crop deprivation. The crops under observation receive six different levels of irrigation from a full irrigation down to only 40% of a full rate. In the case of corn, the ARS team found over a four-year research period that yields ranged from 210 bushels down to 130 bushels across the six irrigation applications.

Already the research has turned up some surprising results. For example, Trout found that corn needs 600,000 gallons of water per acre (from rain and irrigation) to produce 200 bushels of corn.

"After an initial amount of water to the corn growing, the consumption rate stayed about the same through all six levels of irrigation at about 2,500 gallons per bushel of corn," says Trout.

That flies in the face of the traditional belief that crops use water less efficiently as they get more of it. In this experiment, Trout found 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 of the country.

"Corn farmers might do better financially to use full irrigation on a portion of their irrigated acres, rather than using limited irrigation spread over all the acres," Trout says. "Another option would be to grow a different crop that requires less water, if the economics of limited irrigation work for that crop."

The researchers plan to use computer models to test the results beyond the climate and soils on the research farm for a wide range of conditions throughout the central High Plains.