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Calibrating sprayers

Agriculture.com Staff 05/14/2009 @ 8:44am

Farmers are sometimes so focused on spray tip condition that they may overlook an operating condition fundamental to sprayer accuracy -- pressure.

Uneven application of chemicals and untreated areas of oversize weeds are problems that can happen when there's uneven pressure throughout the sprayer boom. Bob Klein, cropping systems specialist at University of Nebraska-Lincoln's West Central Research and Extension Center, says, "We used to just start calibrating the sprayer and collecting output."

But he explains that it's important to first check the pressure along the boom for a possible restriction in the line. Klein suggests checking and comparing cab pressure with boom pressure. Then, if there is a difference, farmers can make note and compensate to know the exact pressure of the sprayer.

"We usually try to rig the pressure gauge with quick-attach fittings that can snap in place on the nozzle fitting," Klein says. "We like to buy the good glycerin-filled stainless steel gauges. The lesser-quality gauges won't last much more than a year."

Klein says three things affect gallons applied per acre:

  1. Speed. You only apply half the rate if you run the tractor twice as fast.
  2. Application rate. "Remember, anything heavier than water comes out more slowly than water, so we need to adjust the sprayer to compensate," Klein states.
  3. Nozzle spacing. Klein's research suggests 30-inch nozzle spacing is just as effective as the standard 20-inch spacing if 110-degree nozzles are used. He also recommends 30-inch spacing because most farmers plant 30-inch rows. "So if you want to use drop nozzles, you can just add extensions to have drop nozzles," Klein says.

With 30-inch nozzle spacing, farmers can allow for 50% larger nozzles. This may, in turn, let farmers use a lower application rate without having to use exceptionally small nozzles.

Klein also says farmers should be concerned about efficacy and drift when it comes to sprayer calibration.

He says he has seen good results with the new air-induction nozzles. Most older models require pressure of about 50 PSI, whereas the new extended-range nozzles are best set at 30 PSI.

Farmers are sometimes so focused on spray tip condition that they may overlook an operating condition fundamental to sprayer accuracy -- pressure.

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