Giant green circles

Travelers looking out airplane windows while flying across the United States may wonder what creates those giant green circles so visible from 30,000 feet.

The circles are crops irrigated with a self-propelled sprinkler irrigation system that rotates around a central point commonly called a “center pivot system” or “center pivot.”

Center pivots are so common that many people are surprised to learn they have existed only about 50 years. The center pivot's inventor, Frank Zybach received a patent for a “Self-propelled Sprinkler Apparatus” in July 1952.

The center pivot is the first, and most successful, robot for production agriculture. The center pivot can be used to irrigate from one to more than 600 acres. Varying the length of pipe or adding a corner attachment will allow center pivots to irrigate almost any size or shape field. An operator only has to turn on the water pump, start the center pivot and wait until the system completes its journey across the field, which can be scheduled from 12 hours to 10 days, depending on the volume of water applied.

Center pivots are used on about one-third of the irrigated land in the United States. In the Great Plains, they irrigate more than 90 percent, and that percentage is increasing each year.