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Tips for tuning up micro-irrigation systems

The continuing drought confronting many California tree nut producers heightens the need to ensure that drip or micro-sprinkler systems are applying water most efficiently.

It’s important to check these systems regularly to know just how much water they are applying and to identify and fix any problems before they get worse, says Larry Schwankl, irrigation specialist with the University of California-Davis.

Things can change over time, he notes. For example, the pump may not be applying water at the same pressure it once did. Or, the orifices of a micro-irrigation system may be partially clogged, making it difficult to spot any water application problems.

“Knowing the rate at which you are putting on water gives you the more control over this very limited resource,” he says.

He offers these suggestions for fine-tuning your micro irrigation system:

• Determine the water application rate.

• Collect the water coming out of a drip emitter or micro-sprinkler for 30 seconds. Then covert this figure to a discharge rate in gallons per hour.

• Make sure you check application rate throughout the orchard to get a good representative sample. Base your calculations on the average application rate.

• Measure uniformity of water application.

Because of variations in coverage of any irrigation system, it’s important to measure which trees are getting more and which ones are getting less. Schwankl recommends measuring water discharge from 36 emitters or sprinklers in an orchard — some at the head of the system, some in the middle and some at the end. “Compare the 25 percent of the trees getting the least amount of water and compare that to the average,” he says. “That gives you a good idea about how much extra water you need to apply so that those trees in the lowest 25-percent area get an adequate amount.”

• Maintain the system.

The primary factor affecting uniform water application is clogging of lines and orifices, he says. Use good filters, whether screen, disk or sand media and clean them of sand and other debris they collect. The dirtier the water, the more frequent the need for maintenance.

Bacterial slimes and algae and other organic materials can also clog a system. “Almost any surface water will have biological contaminants to some degree,” he says. A biocide, chlorine or a copper-based product can control this problem.

Chemical precipitates, like calcium carbonate (lime) or iron, can be eliminated by treating the system with products that control water acidity.

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