Troubleshooting
Why drip system uniformity matters
F
or decades, using drip irrigation (including drip tape, drip emitters or microsprays) has helped many
farmers increase crop yield and quality while at the same time improve water and resource use efficiency. However, no matter how beneficial a drip system is expected to be, factors such as aging equipment, lack of maintenance or improper design can have a significant impact on the system’s ability to deliver irrigation water and nutrients efficiently and effectively.
This ability is known as the system’s distribution uniformity (DU) and is an
excellent indicator of how well it is operating. It’s a measure of how evenly water is applied across a field during irrigation. For example, if one area of a field is receiving 10 gallons of water per hour from an irrigation system, but another area of the field in the same irrigation set is receiving six gallons per hour, this is considered poor DU. This creates a problem because areas that are receiving less water need to be watered for longer, which means other areas of the field are receiving more water than needed. Ideally, DU audits measure above 90 percent
and are conducted yearly by mobile labs, consultants or trained on-farm personnel.
Recent on-farm irrigation system DU analyses conducted by mobile labs were reviewed in a report by AG H2O and the Center for Irrigation Technology. The report reveals that a significant percentage of existing drip systems have poor distribution uniformity. A drip system with poor DU has a ripple effect, translating into a waste of water, fertilizer and energy, lost profits and possible degradation to the environment (see table below).
Impact of poor DU performance | 80-acre system Inputs Fertilizer (lbs/acre)
Water in acre feet (surface water supply) Energy cost/acre @$0.18
Increased quantity of inputs per acre per year due to DU degradation (based upon a new system DU of 90%) Distribution uniformity (DU) 75% 70% 60 53
85% 80% 17 17
35 33
$5.00 $15 $25
80 77
$35
65% 60% 110 103 $45
140 133 $55
How to use this chart: If a grower wants to apply 3 acre feet of irrigation to all parts of the field, then depending on the degradation of uniformity, the grower must compensate by overapplying in some of the field. This chart calculates the wasted water, energy and fertilizers based on the overapplication. Prepared by AG H2O, Sept. 2017
Percent of farms measured DU and impacts of poor DU performance excerpted from AG H2O presentation to CAIA on “Management of Agricultural Energy and Water Use With Access to Improved Data”
24 Irrigation TODAY | January 2019
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