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Center pivot irrigation is a way to irrigate crops by use of irrigation pipes that rotate around a central pivot. It is also sometimes called central pivot or circle irrigation. With this method, a circle-shaped area around the pivot is watered, and this is often the cause of circular patterns seen in aerial photos of cropland. The equipment used for this type of irrigation can also be altered to move in a straight line. In such a case, it is known as a linear move irrigation system.
The parts of a center pivot irrigation system generally include pipes, trusses, wheel towers, and sprinklers. Water is fed from the central pivot point through the pipes, and to the individual sprinklers. The pipes are usually connected and held up by the trusses, which are mounted on the wheel towers. The sprinklers are located along the length of the pipes.
Center pivot systems move in a circular motion, with the pace set by the outermost wheels. The inside wheels, which are located between pipe segments, feature angle sensors that determine when the wheels rotate in order to align the pipe segments. Most systems are powered by electric motors, but hydraulic power may also be used.
A common length for center pivot irrigation systems is 1,320 ft (400 m), and this size of system can irrigate about 130 acres. Other lengths are also used, but generally do not exceed 1,640.42 ft (500 m). Systems are usually stationed at a single location, but can also be towed between two locations, so that a larger area may be watered with one system.
Most sprinkler systems in center pivot irrigation are drop systems, that feature a U-shaped, or gooseneck, pipe fastened to the top of the main pipe. Sprinkler heads are positioned only feet away from the crops to limit wind and evaporation losses. Alternatively, drops may be used in a system called low energy precision application (LEPA) to deposit water the soil directly, through the use of drag hoses or bubblers.
One advantage of center pivot systems is that, while they require reasonably flat terrain, they are able to function on more uneven terrain than are most other irrigation systems. The amount of water applied can be adjusted by changing the speed of the system, and center pivot systems can also be used to apply some types of fertilizers and pesticides. Another advantage is that a relatively small amount of labor is required. A drawback, however, is that the initial cost of center pivot irrigation can be considerable compared to other types of systems.