Center-Pivot systems and lateral move irrigation machines

Center pivots are a form of sprinkler irrigation consisting of several spans joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The machine is fed with water that comes from the Pivot pad.

Center-Pivots are typically less than 500 metres in length (circle radius). To achieve uniform application, center Pivot systems require a continuously variable emitter flow rate across the radius of the machine. Nozzle sizes are smallest at the inner spans to achieve low flow rates and increase with distance from the pivot point.

Most center pivot systems now have drops hanging from goosenecks attached at the top of the pipe with sprinkler heads that are positioned a few feet above the crop, thus limiting evaporative losses and wind drift. Pressure regulators are typically installed upstream of each nozzle to ensure each is operating at the correct design pressure.

Crops may be planted in straight rows or are sometimes planted in circles to conform to the travel of the center pivot.

Originally, most center pivots were water-powered. These were replaced by hydraulic systems and electric motor-driven systems. Most systems today are driven by an electric motor mounted at each tower.

For center pivot to be used, the terrain needs to be reasonably flat; but one major advantage of center pivots over alternative systems is the ability to function in undulating country. This advantage has resulted in increased irrigated acreage and water use in some areas.

Linear/Lateral Move Irrigation Machines

The above mentioned equipment can also be configured to move in a straight line where it is termed a linear move or lateral move irrigation system. In this case the water is supplied by an irrigation channel running the length of the field and positioned either at one side or midway across the field width.

The motor and pump equipment is mounted on a cart adjacent to the supply channel that travels with the machine. Farmers may opt for linear moves to conform to existing rectangular field designs such as those converting from furrow irrigation.

Lateral moves are far less common, rely on more complex guidance systems and require additional management than compared to centre pivot systems.

Vehicle collides with Pivot Irrigation System

State police are looking for the driver of a vehicle who fled after colliding with a Pivot irrigation system southwest of Bridgeville.
Police say a faulty stop arm on the irrigation system – a large metal structure more than a thousand feet long that moves on wheels around a central pivot point to water farm crops – placed it onto Cannon Road between Wesley Church Road and Federalsburg Road, where it was struck by the car traveling east about 2:45 a.m.
The collision left both the vehicle and the irrigation structure inoperable. The occupants fled after removing the license plates from the vehicle, police said.
They said there was no sign anyone was injured. The pivot had to be removed from the vehicle by a towing company, which then removed the vehicle.
The Bridgeville Fire Department and the De Department of Natural Resources and Environmental Control responded to remove hydraulic fluid that spilled onto the road. The road was closed for about two hours.

Evaluation of a Center Pivot irrigation system

Here is the evaluation abstract of a central Pivot irrigation System (CPIS), made in Brazil from a technical and economic point of view. The profitability of the system was simulated using real data obtained from a farm located in Chile, projected over a time horizon of ten years.

Internal Rates of Return were estimated on two crops that frequently use CPIS maize for seed and maize-for grain, assuming a decreasing capital allocation and an increasing governmental subsidy, in the terms provided by Chilean Law 18.450.

From a technical standpoint, results showed that the operation parameters agreed with the specifications of the manufacturer. The Hermann and Hein Coefficient of Uniformity obtained was 86%, classifying the area irrigated as «well watered».

The Distribution Uniformity parameter obtained was 79%, an adequate result for the crop and soil conditions of the test.

The Internal Rate of Return obtained for maize for-seed varied from 23% to 103% for the range of 100% to 25% of self-financing.

For the case of maize-for-grain the investment is profitable only with a maximum of 70% of capital allocation from the part of the farmer, implying that the minimum subsidy required from the part of the State is 30%.