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Are Your Nozzles Costing You Yield?

New center pivots head to the field designed right down to the last nozzle to apply water as uniformly as possible across a field in order to maximize yield. 

So when those nozzles become worn or are plugged, water distribution is jeopardized resulting in over- and underwatered areas in the field. This not only directly affects yields cutting them by 10% to 15% or greater (according to past university research) but can also cause runoff, soil erosion, deep percolation of water and nutrients, and anaerobic soil conditions (plant oxygen stress), warns Daran Rudnick, Extension irrigation engineer, and Rodrigo Werle, cropping systems specialist. Both men are with the University of Nebraska.

“Consequently, poor water distribution can have a negative effect on a farm’s net return as well as lead to potential environmental concerns,” Rudnick adds. 

space to turn around

Alhough other pivot components can affect distribution, the vast majority of problems are caused by faulty nozzles as well as pressure differences along the length of the spans, Rudnick and Werle point out. Faulty nozzles can consist of:

Missing, clogged, and worn nozzles.

Stuck sprinklers.

Out-of-sequence nozzle packages.

Pressure differences along the pivot can be attributed to elevation change and pipeline friction losses, Werle points out. “When the sprinkler design flow rate varies by at least 10% for more than 15% of the system due to pressure differences, the use of pressure regulators is encouraged,” he adds.

The Nebraska Extension NebGuide G888, Flow Control Devices for Center Pivot Irrigation Systems provides in-depth information of working principles on pressure regulators and includes guidelines for selecting a regulator.

lack of constant pressure

“When regulators stop functioning properly due to a worn-out diaphragm or spring, they no longer provide the desired constant outlet pressure and consequent flow rate,” Rudnick adds. “One visual observation of a nonfunctioning regulator is when water is spraying out of the side of the regulator. If you have concerns that your regulators are approaching their useable life, contact your irrigation equipment dealer to have your regulators tested.”

Rudnick offers an inspection video shot in the field: It has tips on locating the mechanical causes for poor uniformity. You can view that video at itc.tamu.edu/documents/extensionpubs.

In some cases, obvious or easily noticeable pressure issues can be identified, such as the broken gooseneck connections. But stuck sprinklers or clogged nozzles may be less noticeable, especially if the sprinklers are on drops in a tall crop canopy.

use a drone

Aerial or drone imagery can spot nozzle problems if that problem is causing crop stress from lack of water. But aerial imagery can detect all distribution problems. So Rudnick and Werle recommend using catch cans set out in the field to detect distribution problems. Evenly distribute cans of equal size across the pivot, and measure the water they collect to pinpoint variations.  

To identify developing issues with pressure regulators or sprinklers, record and observe your system’s flow rate and pressure over time. That way, you can watch for changes, Werle adds.

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