Standards and Methods for Evaluation of Irrigation System Uniformity
Two commonly accepted standards or methods are available as guidelines for performing evaluations of Irrigation System Uniformity.

  • NRCS Handbook — Available at your local Natural Resource Conservation Service office or
Pivot Extensions (cornering arm or Z-arm)
Some center pivot irrigation systems are designed to expand the wetted area to allow coverage of corner or odd-shaped fields, often referred to as cornering arms or Z-arm. These systems require two separate evaluations if the extension accounts for 30 percent or more of the irrigated portion of the field. One evaluation will evaluate the system while extended, and a second when the arm is not deployed.
Overview of Evaluation of Irrigation System Uniformity Guidelines (center pivot)

  • Have the producer walk the system length and note any application problems while the system is applying water. All known application problems need to be corrected before doing an evaluation of Irrigation System Uniformity.
  • Have the producer start the system and establish a setting for his normal application (avoid weather extremes).
  • Run the system for 10 minutes or more without changes to water supply system.
    • Place catch cans in a line from the center pivot point past the outer edge of the wetted area.
    • Catch cans should be placed to form a straight line from the pivot point to a point on the outer edge of the wetted area.
    • Space catch cans 20 feet apart for system overhead impact sprinklers, and 10 feet apart for all other center pivot application systems.
    • Place catch cans with opening at a height above the crop, or in a field opening width four times greater than the height difference between the crop and catch can opening.
    • A drop of mineral oil may be added to each catch can to minimize evaporation if a reading cannot be taken immediately and conditions favoring evaporation are prevalent.
    • If the catch can placement falls into the wheel tracks, it may be moved one to two feet to avoid damage.
  • Record the number of catch cans placed, the producer’s intended application, catch can opening diameter and other pertinent information. A sample record sheet to use for data collection follows.
  • Record volume collected from each catch can (ml.).

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