Improving center pivot irrigation system uniformity
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Irrigation system uniformity is the ability of an irrigation system to apply even amounts of water to all areas within an irrigated field. In simple terms, if the producer’s goal is to apply one inch of irrigation water, the system will apply one inch of irrigation water in each area. Areas of the field that receive under or over the goal will receive under or over the goal for all applications, multiplying the error.
Sprinklers that over and under apply water by 40 percent will receive 0.6 inches (if under) or 1.4 inches (if over) of irrigation water each time the system attempts to apply one inch of water. By the end of the season, areas requiring eight inches of irrigation water will receive 4.8 inches (if under) or 11.2 inches (if over) of irrigation water. To compensate for the lack of uniformity, producers often apply enough water to prevent drought symptoms in the under-watered areas, leading to over application in parts of the field. By improving system uniformity, producers can reduce overall water use. Using the example discussed above, if 100 pounds per acres of nitrogen is applied through the irrigation system some areas will receive 60 pounds and others 140 pounds.
Irrigation system uniformity evaluation is conducted by sampling the output from a system and identifying areas of the sprinkler package that need improvement. Many machines operate at about 75 percent uniformity, making 10 -15 percent improvements in efficiencies achievable. Most common correction is made in the zone of interface between the end gun and the sprinkler package water supply. With proper adjustment of the end gun and a careful match between water supply volume/pressure and the sprinkler package requirements, almost all center pivot irrigations can achieve a 90 percent rate of uniformity of application or higher.
As a Michigan State University Extension irrigation educator, I have worked on the issue of application uniformity for almost two decades. During that time, I have found very little system uniformity performance differences between newer systems and older systems. In Michigan and Indiana, equipment wear is minimal. The issue of low performance is more likely to be depend on whether the system was assemble correctly when installed and if the sprinkler package was designed for the water supply volume and pressure actually delivered to the system.
MSU Extension, working in cooperation with the Michigan Groundwater Stewardship Program, has been teaching technicians, producers, agency personnel and farm employees a procedure for evaluating irrigation system uniformity since 2004. Several Conservation District offices offer these evaluations as a service to irrigators. To learn more about the procedure, view example results from previous training or download the Irrigation system uniformity spreadsheet visit our website.
