5.3 Water Application Uniformity

There are other ways to assess the uniformity of irrigation. For example, look at the crop and the uniformity of growth, especially perpendicular to the irrigation sprinkler head.

If, after a long period of time under irrigation, the crop seems to vary in growth rate across a growing bed or from one end to the other, then suspect a problem with watering uniformity. Check with the grower to see if hand watering is used on just parts of the growing bed, such as the distant end or along the outsides to supplement overhead irrigation.

Non-uniformity may be caused by the incorrect or non-uniform operating pressure or by the wrong spacing of sprinklers/nozzles. The wrong nozzles may also have been used. This situation should not be found very often.

Uniformity of application can be checked using a grid of empty straight-sided cans set in the irrigated area. This catch can method of evaluating uniformity is simple and very good.

  • The primary requirement is that the open diameter of the container should be exactly the same.
  • Set the cans on a grid that places them on lines between sprinklers, along the edge of the growing bed, and inside the growing bed in a symmetrical pattern. Sprinklers typically discharge more water close to the sprinkler and less at the outer edge. Use 20 or more catch cans to achieve better results (for both overhead sprinklers and drip emitters); set them out in a uniform grid pattern. Check for variation between cans. This method evaluates the water application uniformity.
  • Sprinklers should overlap enough to even out the total application rate. Place the cans, run the irrigation cycle, and then measure the collected water in a marked measuring container. Avoid windy days because the wind will distort the application pattern of the sprinklers.
  • Write the results onto a sketch of the test area. The goal is to have less than 10 % variation between all of the containers.