If you fly across the United States, large areas of the Midwest and plains are covered with neat circles. These are made by a process called center-pivot irrigation. A long water pipe is carried on a series of wheels, and each pair of wheels is driven by a motor. Rods and cables between the sets of wheels turn the motors on and off, and keep the pipe straight as it revolves around a central pipe. The water comes from a well nearby.
The rig shown here is parked in a field in Wisconsin. One of the spray heads is atop the pipe at far right. In a rainy climate like Wisconsin, center-pivot irrigation supplements natural rainfall and makes the difference between an average harvest and a good one. In dry regions like the plains, it makes it possible to farm areas that were too dry to farm before this method was invented. In those places it makes the difference between farming and not farming.
Center-pivot irrigation makes it possible to farm land that is otherwise too dry, but it wastes a lot of water because a great deal evaporates in the air instead of reaching the soil. Also, the water comes from underground, where it has been stored for thousands of years. Over much of the plains, the water is coming from a layer called the High Plains or Ogallala Aquifer. This water is being used much faster than it is being replaced, and in some areas the water will probably run out during the 21st Century.
Created 25 November 2005, Last Update 21 December 2010
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