thumb|400px|A satellite image of circular fields characteristic of center-pivot irrigation, Kansas

thumb|200px|Farmland with circular-pivot irrigation

Center-pivot irrigation (sometimes called central-pivot irrigation), also called water-wheel and circle irrigation, is a method of crop irrigation in which equipment rotates around a pivot and crops are watered with sprinklers. A circular area centered on a pivot is irrigated, often creating a circular pattern in crops when viewed from above (sometimes referred to as crop circles, not to be confused with those formed by circular flattening of a section of a crop in a field). Most center-pivot systems were water-powered; however, today most are propelled by electric motors.

Center-pivot irrigation systems are beneficial due to their ability to efficiently use water and optimize a farm's yield. The systems are highly effective on large land fields.

History

On March 23, 1914 James A. Norton of Odebolt, Iowa, filed the patent for the center-pivot irrigation system. On August 17, 1915, it was granted as patent #1150144. The patent drawings shows multiple pairs of wheels supporting a pipe that is moved in a circle around a central pivot point. The description is: Watering arrangements making use of movable installations on wheels or the like movable around a pivot center.

Center-pivot irrigation was invented in 1940 by the farmer Frank Zybach, who lived in Strasburg, Colorado.

Zybach saw success with modified designs, which improved the systems operational efficiency. In 1954, he licensed his patent to Robert Daugherty and his company, Valley Manufacturing. Daugherty's engineers spent the next decade refining Zybach's innovation, making it sturdier, taller, and more reliable, and converting it from a hydraulic power system to electric drive. Daugherty's company went on to grow into Valmont Industries, with Valley Irrigation being its subsidiary.

Overview

Center-pivot irrigation is a form of overhead sprinkler irrigation consisting of several segments of pipe (usually galvanized steel or aluminum) with sprinklers positioned along their length, joined together and supported by trusses, and mounted on wheeled towers.

For a center pivot to be used, the terrain needs to be reasonably flat; but one major advantage of center pivots over alternative systems that use gravity flow is the ability to function in undulating country. This advantage has resulted in increased irrigated land area and water use in some areas. The system is used in parts of the United States, Australia, New Zealand, Brazil,

To achieve uniform application, center pivots require a variable emitter flow rate across the radius of the machine. Since the outer-most spans (or towers) travel farther in a given time period than the innermost spans, nozzle sizes are smallest at the inner spans and increase with distance from the pivot point. Aerial views show fields of circles created by tracings of quarter-mile or half-mile (400 or 800 m) radial irrigation pipes, which consume up to several thousands of gallons per minute." In these systems the water is supplied by an irrigation channel running the length of the field. The channel is positioned either at one side or in a line through the center. The motor and pump equipment are mounted on a cart by the supply channel. The cart travels with the machine.

Farmers might choose lateral-move irrigation to keep existing rectangular fields. This can help them convert from furrow irrigation. Lateral-move irrigation is far less common, relies on more complex guidance systems, and requires additional management compared to center pivot irrigation. Lateral-move irrigation is common in Australia. There, systems are usually between 500 and 1,000 meters long.

Benefits

Center-pivot irrigation uses less labor than many other surface irrigation methods, such as furrow irrigation. This is an example of the Jevons paradox.

In parts of the United States, sixty years of the profitable business of intensive farming using huge center-pivot irrigators has emptied parts of the Ogallala Aquifer (also known as the High Plains Aquifer). The total water extraction from center-pivot irrigation in the area is estimated to be about .

In 1950, irrigated cropland covered . With the use of center-pivot irrigation, nearly of land were irrigated in Kansas alone. At some places, during maximum extraction, the water table dropped more than per year. In extreme cases, wells had to be greatly deepened to reach the steadily falling water table. and international journalists. A May 2013 New York Times article "Wells dry, fertile plains turn to dust"

See also

  • Irrigation management
  • Irrigation in Saudi Arabia
  • Water management
  • Fossil water
  • Hydrogeology

References

Additional sources

  • "The Ogallala Aquifer" Manjula V. Guru, Agricultural Policy Specialist and James E. Horne, President & CEO, The Kerr Center for Sustainable Agriculture, Poteau, Oklahoma
  • USGS High Plains Regional Groundwater Study
  • A Legal Fight in Texas over the Ogallala Aquifer
  • Kansas Geological Survey information on the High Plains / Ogallala Aquifer
  • Rapid Recharge of Parts of the High Plains Aquifer Indicated by a Reconnaissance Study in Oklahoma