A center pivot irrigation system is a mechanized method of watering crops, primarily used in large-scale agriculture. This technology utilizes a long pipeline that rotates around a single, fixed water supply point, applying water to the field in a distinct circular pattern. Center pivots are widely adopted because they offer high water conservation capabilities and minimize the labor associated with field irrigation.
Core Mechanical Components
The system’s fixed anchor is the central pivot point, typically a stationary tower bolted to a concrete pad that connects to the main water source. This central point houses the control panel and a riser pipe that supplies water to the rest of the structure. The pivot swivel, an elbow-shaped fitting, allows the pipeline to rotate 360 degrees while maintaining a continuous flow of water and electricity from the central point into the moving structure.
Extending radially from this anchor are the trussed spans, which are long sections of pipe made of galvanized steel or aluminum that carry the water out over the field. These spans are supported by steel trusses designed to evenly distribute weight between the supporting towers. The spans are connected end-to-end with flexible joints, allowing the entire structure to move over uneven terrain while remaining straight.
The pipeline is carried above the crop canopy by drive units, also known as towers, which are spaced every 35 to 55 meters along the length of the system. Each drive unit consists of a motorized base with a pair of wheels, usually powered by an individual electric motor. The motorized towers move the entire structure in a circular path, and each unit contains a tower box with controls and sensors to manage movement and maintain alignment.
The sprinkler package is mounted along the length of the span pipeline. Modern systems utilize low-pressure spray nozzles or drop tubes, which suspend the sprinklers closer to the crop canopy to minimize water loss from wind drift and evaporation. These low-energy precision application (LEPA) and low-elevation spray application (LESA) systems often operate at a pressure of 10–25 psi, a substantial reduction from the 40–80 psi required by older impact sprinklers. Pressure regulators are installed upstream of each nozzle to ensure a consistent flow rate and uniform water application across the entire radius, regardless of changes in elevation.
System Operation and Movement
Water is delivered from the central anchor through the riser pipe and into the main span pipeline. The control panel directs the system’s movement, sending electrical signals to the drive units along the span. The system’s movement is typically controlled by the outermost drive unit, which dictates the overall rotation speed of the entire pipeline.
The outer sections of the pipeline must travel a greater distance than the inner sections in the same amount of time. Consequently, the drive units on the outer spans rotate their wheels faster than the drive units closer to the pivot point. An automated alignment system manages this speed differential, ensuring the entire structure remains straight and cohesive as it rotates around the fixed pivot.
Variable rate irrigation (VRI) can be integrated into the system’s operation. VRI systems adjust the water application rate along the length of the span based on the unique needs of different zones in the field, which are often determined by soil type, topography, or crop variety. This precise control is achieved by individually managing the flow rate of the sprinklers, ensuring that water is not over-applied in one area or under-applied in another.
Land Use and Field Design
The fixed nature of the central pivot point dictates that the irrigated area will be circular, maximizing coverage around the anchor point. This design can leave unirrigated corners in square or rectangular fields. These systems are best suited for fields with relatively uniform and gentle topography, as excessive slopes can affect the alignment of the spans and the uniformity of water distribution.
By applying water directly to the crop root zone using low-pressure sprinklers, they minimize the water lost to evaporation and surface runoff. The use of modern sprinkler packages, such as LEPA, can achieve water application efficiencies of 90–98%. This efficiency makes center pivots a preferred choice in regions where water conservation and precise resource management are priorities.