New Irrigation Method
by John O'Connell
University of Idaho Extension irrigation specialist Howard Neibling is testing how a pivot irrigation
system that delivers water closer to the ground can improve soil moisture in Arco, Idaho.
ARCO, Idaho -- Irrigation experts from University of Idaho and Washington State University are testing a novel method of watering crops they've developed to save considerable water and power for Northwestern growers with appropriate field conditions.
UI Extension irrigation specialist Howard Neibling explained he and his WSU counterpart, Troy Peters, have tweaked an irrigation method long used to supplement natural rainfall in West Texas to better fit growers in the Northwest.
In Texas, pivots fitted for Low Energy Precision Application have hoses that reach the ground, dragging bubbler nozzles that leave moisture bands. Water is deposited beneath the crop canopy, where it's protected from evaporation and drift, improving application efficiency by 5-10 percent. LEPA systems utilize roughly 6 pounds per square inch of pressure, compared with about 20 psi for conventional pivot systems, resulting in energy savings from both pressure reduction and water conservation.
Neibling said irrigators in Idaho experimented with Texas-style LEPA about two decades ago but experienced excessive runoff, given that their pivots put out more than twice the water as is needed in Texas. Furthermore, moisture bands were inadequate to germinate their seeds.
With funding from Bonneville Power, Neibling and Peters are finishing the second year of a three-year trial to prove their method's effectiveness.
"We're both very encouraged with what we're seeing," Neibling said.
They doubled irrigation hoses per pivot span for improved field coverage and raised the hoses to a foot off the ground, fitting them with spray rather than bubbler nozzles for more even distribution. They've avoided runoff problems in flat fields with good soil infiltration, having tested LEPA in wheat, alfalfa, oats, mint, silage corn, grass seed and beans. To draw a good comparison, they've converted just a few spans of each pivot to LEPA. Trials have been conducted in Malta and Arco, Idaho, parts of Washington and Oregon and in Nevada, where growers interested in the technology contracted with Neibling.
Neibling has yet to tabulate soil moisture results, but Arco grower Mark Telford witnessed the water savings in wheat during a windy June.
"With the higher (conventional) nozzles you could just see the water carrying off in the sun," said Telford, who plans to use LEPA in potatoes next season.
Bonneville Power mechanical engineer Dick Stroh said Nevada grower Kirk Dahl was so impressed by the new method of LEPA, he intends to convert all of his pivots, and his neighbors are also interested in trying it. Stroh estimates the cost of converting an entire pivot to LEPA at $10,000, and a Bonneville Power program would pick up roughly $3,000 of the cost. He said a typical canal irrigator can expect to save 30 percent in power through LEPA.
The researchers are also testing humidity levels in LEPA fields, hopeful that it may reduce crop diseases.
Using bicycle wheels and pivot nozzles supported by a tent frame, Neibling invented a mobile sprayer to simulate his brand of LEPA. Next season, he and Peters will use the sprayer to collect soil infiltration data from several fields. With the data, they plan to create a web tool, allowing growers to input their specific cirumstances and determine if LEPA is a good fit for their operations.
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