Center Pivot Irrigation (CPI) is a highly mechanized method of crop watering that has become a defining feature of large-scale agriculture. This system involves a long, self-propelled pipeline that rotates slowly around a central anchor point, delivering water to the crops below. When viewed from above, the system’s rotation is responsible for the distinct, massive circular patterns visible on farmland. CPI automates the process of irrigation over vast areas.
Components and Function
The physical structure of a center pivot system is built around a stationary central tower, which serves as the hub and the fixed water supply connection. This pivot point is anchored to a concrete base and houses the main control panel, where the system’s operation and movement are managed. Extending outward from the central tower is a long, pressurized pipeline, often constructed from galvanized steel or aluminum, segmented into sections called spans.
The entire pipeline is held above the crop canopy by wheeled support towers, known as drive units, spaced at regular intervals. Each drive unit is equipped with an electric motor and gearbox that powers the wheels, allowing the structure to move in a continuous, circular path. The outermost support tower sets the pace; an alignment system ensures the inner towers maintain the correct position by moving slightly faster or slower as needed.
Water is delivered to the crops via a sprinkler package, consisting of numerous sprinkler heads or nozzles attached along the pipeline. Modern systems often utilize low-pressure spray heads on drop tubes, which hang down closer to the ground, minimizing water loss from wind drift and evaporation. The flow rate of these nozzles is carefully calibrated to increase toward the outer end of the system, ensuring an even application of water despite the greater distance the outer edge travels during rotation.
Water Use and Application Uniformity
The controlled movement and precise nozzle arrangement of center pivot systems contribute to water application consistency across the irrigated field. This uniformity ensures that all plants receive the intended volume of water, reducing variability in crop growth and yield. Performance is measured using a metric called the Coefficient of Uniformity (CU). Well-designed and maintained systems typically achieve values above 90%, indicating excellent water distribution.
The move toward low-pressure nozzles and drop tubes has significantly increased the system’s water application efficiency compared to older, high-pressure impact sprinklers. By applying water closer to the ground, these modern configurations reduce the amount of water lost to the atmosphere before it reaches the soil, minimizing evaporative losses and wind-related drift. High efficiency, often ranging from 80% to 95%, means the system can apply water at a rate the soil can absorb, thereby reducing surface runoff and soil erosion.
The mechanized and automated nature of the system also translates into a substantial reduction in the labor required for irrigation scheduling and application. Once the system is programmed, it can operate semi-autonomously, providing growers with better control over the timing and depth of water application. This precision allows for the uniform application of fertilizers and other chemicals mixed with the irrigation water, a process known as chemigation, ensuring even distribution across the field.
Addressing Non-Circular Fields
The inherent circular pattern of a standard center pivot system leaves sections of a square or rectangular field—specifically the corners—unirrigated, representing a loss of 15% to 20% of the total available acreage. To maximize the cultivated area, farmers often employ specialized corner systems that dynamically extend the reach of the pivot. These corner systems use an additional jointed section of pipe and a dedicated drive tower that swings out and retracts only when it senses the system is approaching a corner of the field.
The movement of the corner section is controlled by a guidance mechanism, frequently a buried electric cable or GPS technology, that tells the swing arm precisely when to extend and where to apply water. An end gun, which is a large sprinkler mounted at the very end of the main pipeline, works in conjunction with the corner system to maximize the wetted area. While effective at filling in the corners, these mechanisms add complexity and cost to the overall irrigation setup.
A separate mechanized system, known as lateral move or linear move irrigation, uses the same core technology but is designed to irrigate perfectly rectangular fields. Unlike a CPI system, a lateral move machine is not anchored at a central point and travels in a straight line across the field. Water is supplied either from a ditch running the length of the field or via a large hose that is pulled along, making it an alternative for fields where a circular pattern is not desirable.