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Corn+Soybean Digest

Pressure Regulators Boost LEPA Efficiency

Fitting low-energy precision application (LEPA) nozzles with pressure regulators brought big gains in irrigation efficiency for Mike and Gary Friemel.

It's their own version of precision agriculture on their Texas Panhandle farm near Groom.

The brothers' farming operation includes 4,000 acres of corn. They run 13 center pivots, 10 of which are half-mile circles that can water nearly 500 acres in one rotation.

"We don't like to move sprinklers," says Mike Friemel. "With a half-mile system and 18 towers, we can water four times more than a quarter-mile system."

The pivots feature drop tubes equipped with LEPA nozzles that hang 18-24" off the ground. Most tubes are in 60" spacings.

Using charts provided by Seninger, the nozzle manufacturer, the brothers get readings on water applied from each tube, compared to the needed amount.

Pressure regulators help maintain the correct flow.

"We had some regulators, but didn't feel we needed them on all our systems," says Friemel. "When we put in our most recent pivot in 1997, I noticed the first few towers (from the center) had too much spray. That was on a 1,500-gallon (per minute) system. It appeared to be putting out more water than a 2,700-gallon system."

He checked the pivot charts furnished by Senninger with the original nozzle package. Tubes from the first few towers were scheduled to spray at 0.05 gallon per minute (gpm). But the nozzles were putting out 0.90 gpm.

"We were wasting water," says Friemel. "We contacted our irrigation consultant and he suggested regulators. Tests by the Texas Department of Agriculture also showed inefficiencies on unregulated nozzles. I was convinced we needed them on all the systems. We installed them and solved our problem."

The low-flow regulators, fitted between the drop tubes and nozzles, range from 6 to 10 lbs.

A LEPA system can have a 95% or higher efficiency rating. Friemel figures his systems were in the 80-85% range prior to being regulated.

"We improved our efficiency rating 10-15 percentage points," he says.

The Friemels irrigate because their average annual rainfall is 17-18". Their yearly irrigation varies from 24" on full-season, 114-day corn to 14" on short-season, 90-day corn.

The LEPA systems are also used to apply insecticide. By flipping the bottom nozzle pad to the chemigation mode, they can make the water spray upward to the canopy instead downward to the soil.

"With chemigation, we are much more efficient at controlling corn borers and mites," says Friemel.

"You can't get to the insect infestations as well with an aerial application. So we're getting better insecticide coverage and don't have the $3.50/acre aerial application charge. And with the better coverage, we can use a half or three-quarters application rate and still get good control," Friemel says.

Leon New, Texas A&M University ag engineer who helped pioneer LEPA, says that when water is limited, corn yields are higher under LEPA than under conventional pivots.

"Similar yields of corn are achieved with only 67-80% of the water applied by conventional methods," says New. "At least 20% more water will reach the ground in a LEPA system."

He recommends using furrow dikes or other tillage and crop residue to prevent runoff caused by nozzles close to the ground, especially in clay soils. The Friemels have a clay loam soil, but don't use dikes.

"We cultivate to make sure the clay soil is aerated," Friemel explains. "That helps prevent runoff."

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