This article appears in the March 2018 issue of Potato Grower.
Issues like declining water availability and high energy costs are becoming a major concern for irrigators in a world affected by dwindling natural resources. Growers know that more efficient farming practices and irrigation technologies are needed to keep farm profits sustainable and are experimenting with new ways to enhance current technologies.
American growers have looked at LEPA (low-energy precision application) technology, which was developed in the 1980s, and have tested different ways to use these sprinkler heads. The technology was already known for its ability to reduce wind drift and evaporation loss dramatically, so in recent growing seasons, growers have begun installing this technology in new ways to see if they could increase the benefits.
What began five years ago as an experiment is now an award-winning technology found in Texas, Arizona, Nevada, New Mexico, California, Kansas, Colorado and Idaho. Now known as LEPA close spacing, growers are using it for a variety of crops such as potatoes, onions, carrots, alfalfa and corn. It’s also gaining interest in areas where water is regulated, and among forward-thinking growers looking to produce good yields with significantly less water and energy.
Understanding LEPA Close Spacing
LEPA originated from a collaboration of researchers from Texas A&M and Senninger Irrigation. The applicator was designed to deposit water near the soil surface—about 18 to 24 inches above the ground—at low pressures to help prevent wind drift and evaporation. Cotton growers originally used it in the western High Plains of the United States.
In those early LEPA systems, applicators were mounted far apart to irrigate every other furrow. Since this precision application wetted less than half the soil surface, it helped reduce the effects of evaporation, making LEPA 95 percenet efficient in water use.
The new close spacing method adjusts the spacing between heads to 40 inches or less between heads. This adjustment allows growers to maintain the benefits of lower wind drift and evaporation loss and reduced pumping costs while also obtaining:
- A more uniform root zone coverage
- Increased yield using less water
- A chance to leach salts in the soil
- The ability to avoid wetting the plant canopy in row crops
- The opportunity to apply the water needed in fewer pivot passes
- Reduced potential rodent damage to crop and equipment over drip systems
LEPA close spacing has proven so effective that in 2017 the Irrigation Association selected “Close-Spaced LEPA Installations: Saving Water and Energy and Increasing Yields” as the winner of its new Vanguard Award, which recognizes a project executed by a team of individuals, companies, organizations or other group entities that have executed an innovative installation project in the irrigation industry.
Firsthand Experiences
John Maurer from Triple D Ranch in Dyer, Nev., discovered LEPA close spacing bubblers outperformed standard sprinklers over alfalfa. The climate in Dyer—at an elevation of 4,898 feed—is windy with little to no rainfall and very low humidity. The primary soil type is heavy silt clay loam. LEPA close spacing bubblers produced an average of 21.5 percent more bales and tonnage by 6.5 percent during four cuttings over the season on three center pivots. The grower attributes these yield increases to the water application of LEPA close spacing heads. The water application rests on the soil surface and slowly infiltrates, producing lateral water movement in the soil and leaching of salts beneath the root zone.
“The groundwater basin here is depleting like most in any heavily irrigated area,” says Maurer. “It became a concern. So when we started using these and saw what they would do to cut that out, that was a big motivation for me, because it's all about efficiency. We found out real quick that we’ve got more water in the ground and that we could actually cut back on the amount of water. We started seeing the difference in the hay growth. Very seldom do we ever get more hay [from the] second cutting than first. On one particular field, we put the bubblers on right after the first cutting, and for the second cutting in 30 days, we had 40 more bales on one pivot.
“This year when we got the soil samples back, we flushed out a bunch of sodium,” Maurer continues. “We’ve gone from 2.6 down to 1.6, which is pretty substantial. It was the first time that we’ve ever been able to move salt. Now that we have the ability to push water down and flush it out of the root, we can move off salt. I’m excited about what we’re going to be able to do to these fields as we continue to push the water into them.”
Grower Bob Holloway in Mingo, Kan., was able to produce 50 percent more corn with just 250 to 300 gallons per minute thanks to LEPA technology.
“The situation we were in required us to either give up one irrigated circle or find a more efficient means of irrigating,” says Holloway. “I found that with the LEPA bubbler system, it allowed us to apply the water we have available in a more productive way. The water that is being applied is resulting in less surface moisture and more beneficial subsoil moisture. This should be all producers’ goal.”
Irrigation distributors also see the benefits and increased popularity of LEPA close spacing. Rick Grimes, owner of Southwest Irrigation in southwestern Arizona, says almost 99 percent of his company’s sales could be attributed to LEPA technology. In Arizona and California’s Imperial Valley, summer weather brings temperatures upwards of 120 degrees, and evapotranspiration rates range between 0.6 to 0.7 inches per day. This means a grower with 320 acres of land will need at minimum 12 gallons of water per minute per acre just to offset the evapotranspiraiton rates in June, July and August. In their experience, a LEPA sprinkler closer to the ground uses less horsepower and less pressure to achieve the same results as traditional sprinklers that are 3, 4 or 6 feet off the ground. LEPA close spacing lets growers irrigate more acres and save money because they can put more water on the ground more efficiently and get a more uniform crop. “Thirty-inch spacing will come out traditionally between 98 and 99 percent uniformity and distribution of water applied,” says Grimes. “You can’t get that with the sprinkler that’s 10 feet apart and 5 feet off the ground.”
Rod Stilwell has been with American Irrigation in Garden City, Kan., since 2000. Weather conditions in this area are usually windy and dry.
“The main crops around here are corn, wheat, soybeans, milo, alfalfa and potatoes,” says Stilwell. “With close spacing, growers are seeing that they can shut down their systems more often, therefore saving water and energy. It’s a cost-effective way to produce good yields.”
Making it Work
LEPA close spacing systems work better in relatively flat fields with a slope no greater than 1 percent. Circle planting is recommended to keep the applicator centered in the furrow, which not only works to control runoff but also to avoid wetting the crop canopy. Strip-till and no-till practices further help keep water in the rows and allow for better conditions to preserve the soil moisture, minimize evaporation and protect the row from drying out.
Bubble sprinklers perform at low pressures ranging from 6 to 20 psi, using less energy than conventional low-pressure sprinklers, and operate using fewer gallons per minute than conventional spray nozzles.