Irrigation technician Devin Power, Power Hydrodynamics, Inc., Modesto, measures and records irrigation drip-line pressure. Line pressures that are not within system design specifications can be a common problem when addressing nonuniform irrigation water distribution, regardless of system type.Up-to-date irrigation system performance evaluation is essential to efficient irrigation water management. An orchard’s irrigation system should be tested at a minimum of every three years to ensure the system is performing at its highest potential. Evaluating an irrigation system has a similar result to all other annual farm equipment maintenance: It allows for the system to work properly, and frequent system checks help to avoid issues.
“Common system performance problems that I see include emitter plugging or line pressure that isn’t uniform or within system specification,” said Spencer Cooper, senior manager, Irrigation and Water Efficiency, Almond Board of California. “Variation in your system performance could be caused by extra pressure and plugging throughout the irrigation line.”
Impact Sprinkler Pressure Testing
The easiest way to measure the operating pressure of an impact sprinkler is to use a pressure gauge fitted with a pitot tube. The pitot tube is a small, hollow brass tube that should be available for purchase from your local irrigation equipment supplier. A 0–60 psi or a 0–100 psi liquid-filled pressure gauge works well for taking the measurements.
It’s recommended that the same new pressure gauge be used to measure all the pressures when sampling. A new pressure gauge is advantageous, because pressure gauges often become less accurate with use. If multiple pressure gauges are to be used, confirm that they all read the same pressure by measuring a single location with each gauge.
Once the pitot tube is fitted with a pressure gauge, hold the tube in the water stream just outside the sprinkler nozzle, and read the pressure on the gauge. Move the pitot tube around in the water stream until the maximum pressure is noted. With practice, the pressure can be measured at a sprinkler head in only a few seconds. When the measurement is taken, record its location within the orchard on an orchard plot map, or write a good description of its location.
The variability of the pressure measurements is an indicator of the degree of uniformity of sprinkler discharge in the orchard. High variability between sprinkler pressures leads to over-application of water in areas of higher pressure, and under-irrigation in areas of lower pressure.
Evaluating Other Delivery Systems
For evaluation of rotator sprinklers and micro-irrigation delivery systems, step-by-step directions can be found in the section Irrigation System Performance of the online document “Almond Irrigation Improvement Continuum 1.0,” available both as a PDF and a mobile-friendly EPUB. Before you take steps to personally evaluate your irrigation system, check to see if there is a mobile irrigation lab in your area. Mobile labs across the state are sponsored by a local agency (county, resource conservation district, water district, etc.) in partnership with the California Department of Water Resources. They are experts in irrigation system evaluation and will do the evaluation for minimal or no charge. Currently, there are 12 to 15 mobile labs working in California, with five in the Central Valley. Commercial companies in your area may also do irrigation system evaluations for a fee.
“It’s important for growers not only to maintain their irrigation systems, but to also understand the overall impact that maintenance has on the life of their irrigation infrastructure,” said Cooper. “Taking the steps to evaluate your irrigation system and making adjustments has the potential to improve your distribution uniformity, and could also greatly improve your irrigation efficiency.”
If there is more than a 20% difference between pressure readings, it is likely that the application uniformity is not as good as desired. Therefore, consult an irrigation professional, who may be able to make a recommendation to improve the pressure uniformity.
While this article provides recommendations for 1.0 minimum practices, growers can further improve their practices by consulting the Irrigation System Performance section of the Almond Irrigation Continuum Levels 2.0 and 3.0, which include increased frequency and detail in monitoring and improvement.
For more information about the Irrigation Improvement Continuum, please visit Almonds.com/Irrigation.
