Beltwide '06:Saving Water, One Pivot At A Time

Equipping 19 pivot systems in Georiga with variable-rate irrigation (VRI) systems cut water usage by 127 million gallons in 2005, consultant Carl Hobbs reported during a presentation last week at the 2006 Beltwide Cotton Conference. That’s enough water, according to one estimate of per-capita usage, to supply 3,000 people for a year, Hobbs said.

Hobbs and his partner, Jay Holder, operate Hobbs & Holder Precision Irrigation Technologies, and they have been working with farmers, Extension personnel, soil conservationists and university researchers on VRI systems for the last couple of years. Hobbs also is a crop consultant and a regular contact for 2 of our newsletters, PeanutFax and AgFax: Southeast Cotton.

“We’re comfortable advertising a 12% water savings with VRI, but on those systems we saved 19%, on average, and with some systems it was as high as 28%,” Hobbs specified.

A VRI system is equipped with computer-controlled pressure valves that can be turned off or turned down, as needed, across all or parts of the pivot. On a boggy part of the field the electronic controller reduces or shuts off the flow. In a sandy part of a field, the pivot might slow down to increase the gallonage. The controller also can shut off the end gun to prevent it from spraying water into roads, trees or adjoining fields. In addition, water rates can be varied around a circle that contains more than one crop.

Decisions about how to program a pivot are made with aerial imagery, field maps and ground-level evaluations. Initial programming is handled on a desktop computer, then copied to a compact flash card for transfer to the pivot’s controller, which Hobbs described as a specialized spray controller. A GPS receiver on the pivot tells the controller where the nozzles are at any given time.

“VRI puts only as much water in a given part of the field as the crop needs,” Hobbs said. “One grower who waters from a pond told me that until he got the VRI system he had never been able to put three-quarters of an inch of water around the circle without having to slow down at some point to let the pond catch up. A turf grower had never been able to produce grass in one quadrant of his circle because it was too boggy. Now, though, he can reduce the flow on that part of the field, and he’s now growing high-value zoysia in that area.”

Cost-sharing funds from NRCS have helped defray the cost of some VRI equipment installations. Most electric-drive pivots with pressure regulators can be retrofitted, Hobbs said. More installations are planned for 2006 in Georgia and South Carolina. Hobbs said he and Holder expect to set up systems this year in Mississippi and Arkansas.

Not every pivot may be a good candidate for VRI, Hobbs said, and work needs to be done on a suitability index to determine to what extent an investment in VRI would pay for itself. In a level field with a uniform soil type the payback would take longer than in a field with highly variable soil types, for example.

There still are plenty of pivots in Georgia, however, that are candidates for a VRI retrofit. In 1970, Hobbs noted, only 87 pivots could be found in the entire state of Georgia. Today, the state boasts 10,500 systems, which is more than any other state except Texas.

For more information, go to the Hobbs & Holder web site, http://betterpivots.com.