DU Testing | Irrigation Dispersion Rates & Crop Yields

Large acreage farms, depending upon the geographic location, often require irrigation to ensure optimal crop yields. But as any farmer who grows nuts, fruit or row crops knows, it’s prudent to quantify irrigation distribution uniformity rates in an effort to maximize every dollar allocated. How can you, as a grower, ensure that your irrigation system is performing optimally and that the water is evenly being applied to the fields? Distribution Uniformity (DU) Testing is one reliable method to measure an irrigation system’s performance.

DU Testing Accurately Measures Irrigation Dispersion Rates

DU Testing is a key indicator of an irrigation system’s effectiveness but other factors, identified later, may be involved. DU is typically measured during an irrigation audit in an effort to assess how evenly irrigation water is being applied to the crops. With the irrigation sprinklers turned on, “catch cans”, or catchments, are used to collect water samples at pre-determined points within a “grid” pattern around your field.

When the DU Test is complete, the volumes collected in all the cans spaced around the grid are recorded. Disbursement uniformity is then calculated using a ratio that looks at the average water volume, in millimeters, applied to the driest quarter of the grid, along with the average water volume applied across the whole grid. This calculation is referred to as the DU lq ratio, short for the Low Quarter DU. The higher the ratio the better the whole field irrigation coverage is, while a perfect score of 1.0 DU lq, equates to 100% dispersion efficiency.

Above or below average figures vary depending upon the type of irrigation system deployed on the test field. Here are the desirable DU ratios broken down for each irrigation system:

.85 or 85% for fixed sprinkler and travelling gun
.90 or 90% for center pivots, lateral moves, and boom
.95 or 95% for micro-sprinkler and drip

If your DU Test ratio falls below these numbers, your irrigation water is not being evenly applied.

Potential Applications of DU Test Results

Naturally, if you’re a farmer whose DU ratio is sub-optimal, the unequal irrigation water dispersion falling upon your field is a concern. For example, it may indicate that you have faulty sprinklers or pressure problems somewhere within your irrigation system. However, the amount of water leaving the sprinkler heads doesn’t necessarily equate with levels reaching crop roots below ground. Other factors that may influence the actual water volume between the catchment level and root zone include:

Surrounding plant canopy
Root depth
Root access due to influences like thatch and mulch
Varying field slope levels
Air temperature and water evaporation
Soil firmness and moisture saturation

Don’t Allow Poor DU to Threaten Your Next Yield

In the end, low irrigation dispersion uniformity may cause variations in crop yields and quality. Inefficient water use and higher costs are also a concern for growers. Field applied nutrients and fertilizers could also unexpectedly get washed away from the roots. If you farm, it’s always advisable to allow a professional to conduct a complete irrigation audit on your fields whenever dispersion uniformity is in question.

For more information on DU Testing, or to get a free price quote on your next irrigation project contact us now using the form to the right or click here to learn more about our installation services.

Above or below average figures vary depending upon the type of irrigation system deployed on the test field. Here are the desirable DU ratios broken down for each irrigation system: