Jay Capasso, UF/IFAS Extension, Jason Mallard, UGA Cooperative Extension, Phillip Edwards, UGA Cooperative Extension

Understanding Irrigation Distribution Uniformity (DU) and Efficiency: Why It Matters for Growers

Irrigation is an important tool for maximizing crop yield, but to truly optimize water use, it’s important to understand two key concepts: Distribution Uniformity (DU) and Irrigation Efficiency. Here is a breakdown of each term’s meaning and how it impacts your operation.

What is Distribution Uniformity (DU)?

Distribution uniformity meaures how evenly water is distributed across your field. Achieving a DU of 90% is possible for both center pivot and linear overhead irrigation systems. This means that 90% of your field will receive water in a uniform, even manner, which is crucial for minimizing water waste and ensuring your crops receive the right amount of moisture. In the Suwannee Valley, mobile irrigation labs offer free evaluations of irrigation systems to help growers assess their DU.

The catch can method is often used to calculate DU. This method involves measuring the water collected in various cans placed across the field, with the average of the lowest 25% of the measurements divided by the total average depth of water applied over the entire field.

Benefits of Maintaining Good DU

When you maintain good DU, you reap several benefits:

• Simpler Irrigation Scheduling: You don’t need to irrigate the driest parts of the field as much, saving time and water.
• Reduced Field Variability: More uniform water application means fewer pockets of dry or overwatered areas, making your field more consistent.
• More Accurate Soil Sensor Readings: When variability is reduced, soil moisture sensors give you a more accurate picture of water availability across the entire field.

Distribution uniformity also becomes essential if injecting liquid fertilizer through your irrigation system. With more even water distribution, the fertilizer will be applied more uniformly, resulting in better crop uptake and reduced crop growth variability throughout the field.

Factors That Impact DU

Several factors affect the uniformity and efficiency of your irrigation system. Flow rate variability can result from pressure differences, friction losses, or changes in field elevation. Pressure variations in regulators, which control water pressure in the irrigation system, can cause uneven water flow to sprinklers, leading to inconsistent water distribution. This can affect sprinkler performance and spray patterns, increasing system wear and energy costs. Stable pressure is essential for uniform irrigation. Nozzle wear or clogging creates uneven water distribution, while improper sprinkler spacing or design issues can also lead to variations in uniformity. End gun alignment issues can be problematic when water application from the end gun overlaps areas already covered by overhead sprinklers, leading to uneven water distribution. Environmental factors like wind and plant interference can disrupt water application through sprinklers. Operational practices, such as uneven water application during system startup or shutdown and pipe diameter variations, can also cause inconsistencies. Edge effects, where sprinklers overlap at the field edges, can result in less uniform water distribution.

Irrigation Efficiency: How Does it Differ?

While DU focuses on how evenly water is distributed, irrigation efficiency refers to how much of the water you applied is beneficially used by the crop. The equation looks like this:

Efficiency = Water Beneficially Used / Total Water Applied

For growers in the Southeast, irrigation efficiency generally refers to how much water is beneficially used to meet crop evapotranspiration (ET) or the crop’s water needs. We typically don’t need to worry about leaching salts, which could be a beneficial use of water in arid regions with salinity issues. Other potential beneficial uses of water application, though less common than meeting ET, include climate control or promoting weed germination (to be controlled later through management).

Efficiency can be challenging to measure accurately because it depends on how much water reaches crop roots for uptake. In practice, soil moisture sensors can help measure how much water reaches the root zone, providing insight into your irrigation scheduling and system efficiency.

Using Soil Moisture Sensors and DU and Efficiency

Soil moisture sensors are valuable tools for assessing the efficiency of your irrigation scheduling and system performance. To ensure accurate data, placing these sensors in representative areas of the field is crucial. Placing sensors in locations with poor DU can result in data that does not accurately reflect the field’s overall water distribution. This can lead to incorrect conclusions about irrigation scheduling and system efficiency.

Mobile Irrigation Labs: A Useful Resource for Growers in Florida and Georgia

For growers in Florida, mobile irrigation labs are an excellent resource that can help you evaluate the performance of your center pivot and linear move irrigation systems, providing valuable information on DU and efficiency. In Georgia, UGA Cooperative Extension performs evaluations of client’s center pivot and linear move irrigation systems. With professional evaluations, growers can identify areas where their irrigation system needs improvement. Agricultural cost-share opportunities may be available through the Florida Department of Agriculture and Consumer Services or local water management districts to help upgrade irrigation systems if issues are identified for those enrolled in the FDACS BMP program. In Georgia, opportunities are available through USDA NRCS programs. For more information on your local mobile irrigation lab, see the link below: https://www.fdacs.gov/Water/Mobile-Irrigation-Labs.

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