By Jim Steiert
Correct nozzling is the key to maximum returns on water applied to Southern Plains fields.
Nicholas Kenny, Texas A&M AgriLife Extension irrigation specialist and agriculture engineer, says nozzles should be checked annually and those showing wear replaced. Nozzles may have an infinite lifespan when applying clean water, but not when sand and other abrasives are present in the irrigation water. Sandblasting wears nozzles, and that changes their output just as much as plugging.
Orifices and pressure regulators must be replaced as needed. A 20% pressure variation can mean a 10% sprinkler flow variation. Kenny says "Worn orifices and nozzles can result in 10- to 20% over application."
Pay close attention to outside pivot spans to make certain they are working properly, since they cover the most acreage.
Other things to check include:
* The first couple of sprinkler spans. They are prone to plug as they have smaller nozzles. Keep them clean.
* Re-nozzle when flow changes by 20 to 50 gallons per minute. Adding or removing regulators may also be necessary. As elevations changes, the sprinkler's application uniformity also changes.
* Add an air relief valve to pivots. "All wells pump air that accumulates at the highest point. Draining can create vacuum. An air relief takes care of all this," he said.
* Kenny says day and night application efficiency vary. He recommends offsetting the lap period by a half-day periodically so the whole field receives at least some night irrigation.
* Almost without fail, when the corn crop is tall, the area inside the crop canopy is steamy, and the air temperature hot, a pivot will get stuck—usually in the hardest place in the field to reach. "Be sure the pivot's tires are in good shape with plenty of lug to prevent spinning in low fields that are too wet."
Also, Kenny says, "Eliminate windshield wiping if possible. Big tire lugs help. If a few spans give problems with getting stuck, consider phenolic wheel lugs. Check sprinkler tracks for problem spots. Move wheel tracks periodically," he suggests.
* Replace worn or "iffy," tires now, while the pivot can be easily walked to a turnrow , or the unit is readily accessible before planting. Hard plastic bolt-on tires such as Rhinogators are an option, and can be put on as needed, intermixed with conventional tires.
* "Replace gearboxes before they fail. Motors on the end of pivots are notorious for going out. Check them now, before the busy season. Make sure machine voltage is sufficient to provide proper power to the entire length of the machine.
* "Irrigate during severe weather if possible. A pivot filled with water handles the wind much better," Kenny advises.
* Use bubble modes on sprinkler nozzles running as close to the ground as possible. Research shows you'll waste less water in bubble mode than you do if you use spray nozzles.