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50-plus Years of Center-pivot Irrigation

When Coloradan-turned-Nebraskan Frank Zybach started piecing together his first experimental center-pivot irrigation system in 1947, he was on the cusp of nothing short of starting an agricultural revolution. The rickety contraption was basically a span of pipes only a few feet off the ground, suspended by guy wires, driven by metal wheels, and dragged over the ground by skids. It looked like a Rube Goldberg device for wetting soil.

Only about a half-century earlier, mechanized pumping helped pull irrigation practices out of the Dark Ages. The process of filling irrigation ditches with vast amounts of groundwater meant that farmers were no longer tethered to streams and ponds, or at the mercy of rainfall, to keep their crops alive. But irrigation ditches are wasteful and imprecise, flooding some portions of field while leaving others dry.

In the early 20th century, inventors began demonstrating the first spray irrigation systems. They were cumbersome contraptions of linked pipe that had to be connected to a wellhead, with long spans to set up and operate. Then the whole system had to be manually moved farther down the field and reset. It was hard and muddy work, but it represented the first time that farmers were able to irrigate rather large swaths of field at a single time.

Still, when Zybach – whom history remembers more fondly for his success as an inventor than a farmer – saw a demonstration of an early irrigation system at work, he decided it could be done better. A major limiting factor of those systems was that they were constantly moving in relation to their wellhead hookups. Zybach’s elegantly simple but technically complicated solution would be to use a rotating coupling at the top of the well to supply water to a single arm of pipes that swung in a circle around its water source.

center pivot irrigation system

A center-pivot irrigation system uses low pressure and high uniformity to water a cover crop mix that includes daikon radish in O’Brien, Florida. Credit: USDA NRCS photo by Doug Ulmer

His first iteration used water to drive the wheels. As with any swing-arm mechanism, the farthest end of the irrigator traveled much faster than the end at the center, so the system had to regulate its speed. It did so by using the guy wires to control the water valves that drove the wheels. If one section got too far ahead or behind the rest, the tension on the guy wires would adjust the valves to turn the wheels faster or slower. And since the outer end of the swing arm was moving faster, more water had to be sprayed at one end of the apparatus than from the other.

By 1949, Zybach had refined his system well enough to apply for a patent for the “Zybach Self-Propelled Sprinkler Apparatus.” Three years later, he won the patent and started plans to produce it with the help of a financial backer. But the system encountered skeptics. Not only did Zybach’s system look contrived, it only stood a few feet off the ground (not helpful for crops of meaningful height) and its circle pattern left more than 20 percent of a square field dry.

The first two years of production were slow-going, so Zybach and his partner licensed the design to Valley Manufacturing (known today as Valmont Industries), which was then a relatively young farm equipment company based in Nebraska. With the help – and occasional contention – of Zybach, Valley made improvements on the system’s original design: raising the pipes and sprinklers and developing an electrical drive system. Adding the center pivot irrigation system to its lineup of known farm equipment probably helped legitimize it in buyers’ minds, too.

“Prior to this pathbreaking invention, few had understood how irrigation could change the lives of Nebraskans,” the book Nebraska Moments summarizes Zybach’s invention. “Before 1850 there was little interest in settling Nebraska beyond the 100th meridian because the limited rainfall and lack of trees suggested the area could not support agriculture.” The book notes that the state’s number of wells increased tenfold between 1950 and 1990.

The same explosion occurred in many other states where center pivot irrigation opened up new land to farming. Today, massive crop circles are visible from space in places like South Africa and Saudi Arabia.

According to Western Farm Press, U.S. farming employs roughly 150,000 center pivots across the country – covering more than 20 million acres.

While the development of irrigation technology like the center pivot system unquestionably transformed modern agriculture, that prosperity has not come without its side effects. Today, farming irrigation accounts for about two-thirds of all groundwater use in the Unites States. And in recent years, farmers (especially in the West) have seen the levels of their wells start to drop.

According to the U.S. Geological Survey (USGS), many of the nation’s aquifers are seeing water withdrawn by human use faster than nature can put it back. Nowhere in the country is this effect more pronounced than over the Ogallala Aquifer, which spans the High Plains from Texas to South Dakota. Many counties have seen their average well levels drop by more than 20 feet in only 20 years – some areas have lost an average of more than 40 feet of water – according to analysis of USGS data conducted by the Gannett Company.

LEPA center pivot sprinkler

Low energy precision application (LEPA) center-pivot sprinkler systems meet a 96 percent efficiency rating while providing efficient watering applications to the plant. Credit: USDA photo

When farm wells are drilled, they are typically rated for how many acre-feet of water they can produce over a given period. That number, said Charles Corey, executive director of the Irrigation Research Foundation based in Yuma, Colorado, went largely ignored by most farmers, who watered their crops as they saw fit for decades.

As states like Colorado have come to realize the finite nature of their water supplies, they have started metering wells to track usage and restrict overpumping. That has created a situation where farmers need to look for improved efficiency in their irrigation systems. The calculus of watering starts with getting the appropriate nozzle height and drop size to minimize evaporation and maximize absorption in the soil, and then it gets complicated (smarter) from there.

The nonprofit Irrigation Research Foundation partners with manufacturers to test new farming technologies – i.e. seeds, software, pump systems, nozzles, etc. – on experimental and commercial fields to learn how “to do more with less water,” said Corey, whose research is aimed at helping manufacturers provide better information to their customers in the Ogallala. “That’s our concern: to prevent overpumping and keep this water resource viable for many years.”

The biggest single change to irrigation strategy has been adding the ability to control volume at the nozzles of center-pivot systems. In the past, farmers could adjust the speed of the pivot to increase or lessen the amount of water they applied to the fields. That strategy created huge watering zones that looked like slices of pie if viewed from above.

Today’s new systems give farmers control of nozzles that can release water at varying rates. Now irrigation systems can roll at a constant speed but change volume of output depending on the field’s needs.

“You might have a pack of 134 nozzles, but you get control of every three nozzles,” explained Corey. Each of those groups of three becomes a zone in that pivot’s rotation. “The important part is that once you have that control, then you can get creative with protocol, which consists of formulation,” meaning fertilizers, pesticides, and other applications.

center pivot data download

Two USDA researchers download data about the movement of a center-pivot irrigation system to reconstruct the amount of water and time it took to irrigate an area. Credit: USDA photo by Scott Bauer

Last season, the foundation tested a pivot system by Reinke® that used variable rate irrigation mated with a new Agri-Inject brand fertilizer system that can insert variable amounts of fertilizer into the irrigation zones. As the irrigation rates shift within each zone, so does the amount of fertilizer placed into the water stream. “We are able to control the fertilizer in parts per million per flow (per gallon per minute),” said Corey.

While all new technologies come with their costs, farmers ideally will be spending less on pumping, fertilizer, and pesticides, while maximizing crops yields.

As farmers learn their new systems, they are changing some very basic methods of irrigation. For instance, a recent Farm Journal article describes how Ken Ferrie, the publication’s field agronomist, achieved better absorption in sloping terrain by using multiple field passes at lower flow rates. By allowing smaller amounts of water time to absorb into the soil between passes, the process was able to get better penetration by avoiding runoff and ponding in the field’s problem areas.

This goes to illustrate the level of complexity with which farmers will need to understand their fields and equipment in the future. As the technology allows more precise dispersion of resources, Corey predicts, the industry will see regular use of consultants to test soil, crops, and other conditions, and to develop irrigation and fertilizer prescriptions customized to each field and crop.

As Zybach’s invention changed farming over the last 55 years, it will become the future of irrigation entering its next phase – where yields will continue to be strong, but no drop can be wasted.

50-plus Years of Center-pivot Irrigation

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  • United States
  • Eric Seeger