A calibration test conducted by (from left) Vicki Williams and Cindi Siegel of B&M Crop Consulting and Farm Journal Associate Field Agronomist Missy Bauer pinpointed inefficiencies for Kevyn Van Wert of North Concord Farms.
Irrigated corn growers spend big dollars to ensure their crops get enough water at the right time. But a recent study led by Farm Journal Associate Field Agronomist Missy Bauer indicates that many producers may not be applying the amount of water they think they are. That can affect yield and efficiency of fertigation and chemigation. Not to mention, it can waste energy.
The study was conducted in six Michigan and Indiana fields. Using a technique devised by Lyndon Kelley, an irrigation educator for Michigan State University and Purdue University, Bauer placed collection cups (32-oz. cups from Taco Bell) every 10', in a line from the pivot point to the far end of the irrigated area. She then determined the amount of water that was under- or overapplied in 10' increments down the length of the pivot.
Too little or too much. The study had two goals, Bauer explains: to determine whether the systems were applying a uniform amount of water from end to end and to determine whether they were applying the amount of water for which they were calibrated.
Not one of the six systems was applying as much water as the operator thought. The desired rate in each case was 1⁄2" of water. The average actual rate was 0.41"—82% of what the operator intended.
The measure of uniformity from nozzle to nozzle—the application of water evenly across a field—is called the system uniformity coefficient, expressed as a percentage.
In Bauer’s study, the average system uniformity coefficient for the six systems was 81%.
"You will never get 100% efficiency," Kelley says. "But most equipment is capable of 90% to 92%."
The Natural Resources Conservation Service offers an assistance program to help irrigators improve uniformity to at least 85%. "Almost all systems will benefit from some corrections," Bauer says.
"If the uniformity coefficient is from 80% to 85%, you may need to analyze your sprinkler package, and individual sections will benefit from corrections," Bauer continues. "Below 80% calls for adjusting or replacing sprinklers and making corrections to individual sections."
An inefficient system means some areas get too much or too little water at every irrigation. "A 30% deviation in an 8" application year means some areas receive as little as 5.6" while others receive 10.4"," Kelley says.
The graphs above show deviation from the target application rate in individual fields. The sawtooth pattern indicates the amount of variability. If a system was 100% effective, there would be no variability and the graph would look like a straight line.
Such graphs show you where to look for problems. In field No. 1, the system uniformity coefficient was only 76%, meaning the system was not applying water uniformly. The high points show that the sprinklers near towers 2 and 6 were applying too much water.
The low points in several areas show where sprinklers were applying too little. All sprinklers need to be checked. "This is an older center-pivot system, so some sprinklers may be showing signs of age and need to be replaced," Bauer says.
- March 2011