Irrigation System Performance

Irrigation energy use for center pivot systems can be reduced by lowering the system pressure. However, this can lead to increased runoff due to smaller wetted areas. This section, and the accompanying fact sheet, discusses the issues surrounding lowering the system pressure.
Improving the efficiency of water application is a second way to conserve energy and water [34, 35, 36, 37]. Water application efficiency is a comparison between the depth of water pumped and the depth water is stored in the soil, where it is available to the crop.
Irrigation systems can lose water in various ways:

  • Water is lost to evaporation in the air, or directly off plant foliage,
  • Water is lost at the soil surface as evaporation or runoff,
  • Excess irrigation and/or rainfall may also percolate through the crop root zone leading to deep percolation.

For center pivots, water application efficiency is based largely on the sprinkler package. High pressure impact sprinklers direct water upward resulting in relatively large wetted diameters. Larger wetted diameters result in more opportunity for wind drift and in-air evaporation losses. In addition, when applying one inch of irrigation, high pressure impact sprinklers apply water to foliage for 20-40 minutes longer than low pressure spray heads mounted on drop tubes. The difference in application time results in more evaporation directly from the foliage or canopy for high pressure impact systems. These factors have been used as reasons for converting from high pressure systems to some lower pressure sprinklers. However, caution should be used when converting to lower pressure systems so that surface runoff does not result with the new sprinkler package.

For more on converting to lower pressure technology, see:
> Fact Sheet 2: Converting to Low-pressure Irrigation Technology