Pivot woes stand out in dry year
Finding a silver lining in a dry year isn’t easy. Rings of shorter, stressed corn or soybeans in a pivot-irrigated field mean lost yield in those locations, but they also point the way to problems with nozzles, sprinklers or other water delivery problems that can be fixed before or early in the next season.
“Pivot water delivery problems can easily be overlooked in a normal or wet season, but they show up much more clearly in a stressed year like this,” says Bill Kranz, University of Nebraska-Lincoln irrigation engineer.
• Problem sprinklers and nozzles show up more easily in a dry year.
• In some cases, corn yield dropped by 40 bushels per acre under bad sprinklers.
• Do a check of your pivot early in year when crop is small.
UNL irrigation specialists and irrigators themselves noticed those rings of shorter growing corn and soybeans quite often in 2012 from aerial photos and from roadside windshield observations. “Some systems are growing older and underperforming, but a drought puts the stress on any pivot,” he says.
Kranz says problems can be caused by several things:
• Sprinklers can blow out of their hole, creating a geyser.
• Sprinklers can wear out and stop rotating or rotate out of control.
• Your groundwater pumping level may have declined during the season so that the system flow rate and pressure no longer match the original design.
• Boots, gaskets and other seals start to leak.
• Sprinkler spacing is too wide, leaving rings of corn underwater.
“Each of these issues can result in extra water applied in some areas and insufficient water applied in corn yield by 20 to 40 bushels per acre.
A geyser from a blown-out nozzle creates runoff, cuts pressure for the system and impairs pressure regulators, says Kranz. He’s also seen plugged nozzles that apply no water at all.
On one Nebraska Panhandle pivot, sprinklers attached to drop tubes were spaced too far apart in corn. Right below the sprinklers, yields were 210 to 215 bushels per acre, but between the drop tubes, yields dropped by 40 bushels. “If drop tubes into the canopy are used, sprinklers need to be closer together to avoid this problem. Drop tubes also tend to flop up on truss rods,” he says.
Leaking boots, those rubber fittings between pivot spans, can wear out and split on older systems, affecting pressure. “Most of the problems are easy and relatively inexpensive to fix,” says Kranz. “If pivot delivery problems aren’t fixed, yield losses likely will occur.”
Flying over pivot circles in 2013 won’t be feasible for all, but Kranz advises checking your pivots when crops are small. It’s easier then to look for broken sprinklers and plugged nozzles.
WATERING WOES: An aerial photo of this York County, Neb., soybean field in 2012 reveals improper sprinkler performance that causes rings of water-stressed soybeans. Also notice the blown-out sprinkler and resulting geyser in the middle of the photo.
This article published in the November, 2012 edition of IRRIGATION EXTRA.