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Serving: NE
irrigation equipment in field Tyler Harris
REAL-WORLD CHALLENGES: Growing conditions and overall geography are significantly different in the Oklahoma Panhandle compared with west-central Nebraska.

Takeaways from Oklahoma's TAPS competition

There are differences from the Nebraska program when it comes to managing a variable-rate irrigation system.

Nebraska is the first, but it is not the only state to have a farm management competition. Following the lead of the University of Nebraska-Lincoln's Testing Ag Performance Solutions farm management competition held at the West Central Research and Extension Center in North Platte, Neb., since 2017, Oklahoma State University kicked off a similar TAPS competition at its irrigation site in the Oklahoma Panhandle south of Elkhart, Kan., this year.

This year, the Oklahoma TAPS program was introduced featuring a variable-rate irrigation system. And the VRI system brought some challenges for competitors and competition organizers alike, says Jason Warren, OSU soil and water conservation/management Extension specialist and Oklahoma TAPS organizer. Warren gave an update on the Oklahoma TAPS program at the recent Water Management Field Day in North Platte.

The VRI system, while not covering the full pivot span, allows participants to variable-rate irrigate on the outside three spans. Similar to the Nebraska TAPS program, this VRI system allows nozzle-by-nozzle control on 16-inch spacing. While this brought new options for the program's six participants, Warren notes it presented some logistical challenges.

"We're pumping from 250 to 300 feet deep, and we're pumping from three wells — two of which are running 350 to 400 gallons per minute, and an electric well that's about 200 [GPM]," Warren says. "Historically, we minimize pressure to minimize costs for pumping that deep. We pump for a minimum of 10 pounds at the end of the pivot, and we're using 6-pound regulators. With VRI, we found we needed to increase that pressure. So, we had to down-nozzle to build flow and build pressure. Once we did that, it worked very well."

However, there's another challenge: In the Oklahoma Panhandle, irrigators often lose pressure once other irrigators in the area started to draw down their wells.

"Even with a combined 900-gallon nozzle package, we were only getting 15 pounds at the center of the pivot, and 10 at the end," Warren says. "It's flat terrain, so we don't have much pressure drop from the middle of the pivot to the end. We can use low pressure, and even though we're pulling from deeper into the ground, we can maintain pressure from the inside to outside."

"That was our plan when we started," he adds. "As the season went on, we lost capacity and all of our farmers typically lose capacity to some extent. If they lose too much pressure, they'll have to reduce pump speed and down-nozzle toward the end of the season."

Another challenge in semiarid western Oklahoma is high evaporative losses. When applying nitrogen through fertigation for the TAPS competition, Warren notes they applied about three-tenths an inch of water for every pass to apply 30 pounds of nitrogen.

"That three-tenths was inefficient in our environment," he says. "When growers counted it in their water budget, I don't think they were getting as much water as they thought. We're probably losing one-tenth an inch to canopy evaporation. We used four passes for fertigation, each applying three-tenths of an inch, so overall we lost four-tenths of an inch just on fertilizer."

Along with greater evaporative losses, soils in the Oklahoma Panhandle have a higher water-holding capacity and can handle slower passes of the pivot.

"These guys are used to going slow. We'll start off with a three-quarter-inch turn when we have shallow roots," Warren says. "Then we'll slow it down to one-and-a-half-inch and one-and-three-quarters-inch. Our soils can take it, and we're mitigating evaporative water loss. On these quick turns, we're going to lose water and lose days of effective application. We're going to adjust the TAPS program for that and nozzle everything up to a high capacity and give the option of putting an inch and a half out, or a quarter-inch with fertilizer."

They also ran into technical issues in keeping the center pivot turning.

"It's a 30-year-old pivot, and the person that farmed the ground before us piecemealed everything together," Warren says. "He had Valley gearboxes on a Zimmatic pivot — things that should never work. We had three weeks of running at the end of the season when the pivot never stopped, but for the first two months, it stopped at least once on every turn. We've replaced the gearboxes, and next year we won't have that problem."

Looking ahead, Warren notes his dream for the TAPS program is to create plots for water, nitrogen and planting prescription maps layered over yield data — and using soil moisture probes and models to conduct on-farm demonstrations in the area.

"We can clip as-planted and as-applied data, and once we get yield data, we can combine them and generate a spreadsheet with yields inside strips," Warren says. "The genius of the TAPS program is the fact that most of the time, it's not Extension or companies evaluating products and telling farmers about them. It's farmers engaged in evaluation. If something doesn't work right, they see it. Then we can work with service providers to make it better."

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