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Fall Microirrigation System Maintenance

California Avocado Commission — Microirrigation systems (microsprinklers, drip emitters and drip tape) tend to provide better distribution/emission uniformity than other irrigation methods. However, the miniscule flow passages in these systems can become clogged and thus disrupt the uniformity of water applied to a crop.

Late fall and winter are an ideal time to review irrigation systems for needed repairs or malfunctions. A great resource is the University of California Division of Agriculture and Natural Resources’ (UCANR) webpage that outlines various causes of microirrigation clogging and means of preventing or mitigating the problems.

The first step in alleviating clogs is identifying the problem. Clogs can be caused by:

  • Particulates — sand, silt, clay — from surface water sources
  • Biological materials — algae, bacterial slimes — from surface water sources
  • Chemical precipitates — such as iron and calcium carbonate — from groundwater sources or fertigation

To identify the issues, UC ANR recommends first flushing water from the lateral lines through a nylon stocking or paint straining cloth and examining what material is collected. If you see mineral particles, you have identified your problem. If you notice that clogging tends to occur at the ends of the lines, this also tends to indicate particulate clogging.

If you identify organic matter when flushing the line, then biological materials are the issue. You also can open the end of a lateral line and feel inside the tube to see if it is slimy. If so, biological materials are the source of your problem.

If you note white, crusty materials or reddish staining of the soil near the emitters, this is indicative of chemical precipitates.

Once you have identified the clogging source, you can take steps to address the issue.

Particulate issues can be prevented by regular line flushing and the use of filters. UCANR provides a list of various filters and a table noting which filter to choose based on water source, particulates and irrigation system. To adequately flush the lines, water must flush at least 1 foot per second at the end of the drip line — 1 gallon/minute for 5/8” diameter and 2 gallons/minutes for 7/8” diameter drip lines.

If organic matter is the source of the clogging, the best mode of treatment is a good filtration system combined with use of a biocide to remove the biological contaminants. Visit the UCANR site for a list of filters and the aforementioned “how to choose a filter” table.

If calcium carbonate (lime) or iron is clogging your emitters, strong acid can make either disappear if emitters are left in it overnight. Lowering the pH (6 or below) of the water by injecting common acids — sulfuric acid, muriatic acid or hydrochloric acid — can help prevent clogging due to lime. UCANR provides specific formulas to help growers determine the injection rate needed to alter water pH.

If high iron levels are the source of the clogging, aerating the water to oxidize the iron and then allowing the precipitates to settle before irrigating (a reservoir or settling basin is necessary) is the most practical option. Common acids also can be injected to decrease the pH of the water (4 or less).

For more information on routine microirrigation tasks, visit the UCANR website.

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