1952: Frank Zybach gets a patent for the center-pivot irrigator. Hundreds of thousands of crop circles will appear on landscapes around the world … eventually.

You’ve seen ‘em if you’ve flown across farmland in the United States or other nations: big green circles of irrigated land, making repeated dot patterns. But they weren’t always there.

Zybach grew up in Nebraska but was farming in Colorado in 1947 when he saw a demonstration of modern movable irrigation. Workers were moving and connecting pipes fitted with sprinkler heads from one part of a field to another. Sprinklers could beat a couple of problems: uneven, hilly terrain and the tendency of water to run into sandy ground before getting to the end of the ditch.

But Zybach, a lifelong tinkerer, saw something more: Why have humans set up, take down, move the equipment and repeat? Why not have the equipment move itself?

Zybach built his first prototype within a year. It rotated around a center wellhead. Guy wires that were attached to support towers held the sprinkler-fitted water pipes above the ground. Control wires and two-way water valves kept the towers in line. The first support towers moved on skids, but Zybach soon replaced those with wheels propelled by the irrigation water itself.

He applied for a patent for the “Zybach Self-Propelled Sprinkling Apparatus” in July 1949. He knew he needed to improve his invention — making it tall enough to work for corn, among other things. So, the same year he got his patent, he moved back to Nebraska and went into business with a friend, A. E. Trowbridge.

The duo didn’t immediately succeed, partly because Zybach kept making improvements before Trowbridge could sell the models they’d already manufactured. They sold the patent rights for a 5 percent royalty to farm-equipment manufacturer Robert Daugherty of Valley Manufacturing (later Valmont) in 1954.

Valley built only seven systems the following year, but it kept on improving the device. Variable pressure let farmers apply different amounts of water on each full rotation. They could apply fertilizer and pesticides automatically, too. End guns let water reach those dry corners between the circles. Business took off in the 1960s. The amount of land tended by one irrigation worker quadrupled from about 400 acres to 1,600 acres.

More than a quarter-million center-pivot irrigation systems now water fields around the world. Modern systems run in forward or reverse on rubber wheels driven by electric motors.

The control sensors that keep the support towers in line have evolved from simple mechanical linkages to computerized sensors. Some systems use GPS and wireless to control water flow. They take directions from laptops and cellphones. Sophisticated mechanical trusses, not wires, support the pipes.

But what about those empty corners between the circles? Some countries now arrange their circular fields in large, hexagonal patterns to minimize the unsprinkled areas.

That’s hardly practical in the United States and elsewhere where land holdings have already been divided up in big, old-fashioned squares. So, the up-to-date center-pivot systems rely on low-voltage, radio-signal wires buried in the corners of the field. A sensor at the end of the pivot arm picks up the signal and telescopes the pipe outward toward the corner, then retracts again, following the border of the field.

As that technology spreads, the circles you see from your jet-plane window seat may someday be a thing of the past.

Source: Wessels Living History Farm

Photo: Center-pivot irrigation sprinklers rotate around a water supply to create a circular field of crops. (Courtesy U.S. Geological Survey)

This article first appeared on Wired.com July 22, 2008.