Even Pressure A Must In Calibrating Sprayers
May 9, 2008
Uneven pressure throughout the sprayer boom can mean uneven application of chemicals and later, untreated areas of oversized weeds, said a University of Nebraska-Lincoln specialist.
"We used to just start calibrating the sprayer and collecting output," said Bob Klein, cropping systems specialist at UNL's West Central Research and Extension Center at North Platte. But it's important to check pressure all along the boom first because there might be a restriction in the line.
Klein advised checking and comparing cab pressure with boom pressure. If there's a difference, the producer can make a note and compensate so that he or she knows the sprayer's exact pressure.
"We usually try to rig the pressure gauge with quick-attach fittings that can snap in place on the nozzle fitting," Klein said. "We like to buy the good glycerin-filled stainless steel gauges. The lesser quality gauges won't last much more than a year."
Three basic things affect the gallons applied per acre, Klein said.
First is speed. If the producer runs the tractor twice as fast, he or she applies half the rate, if nothing else is changed.
Second is nozzle spacing. The typical nozzle spacing is 20 inches, but Klein's research indicates that a 30-inch nozzle spacing is just as effective if 110-degree nozzles are used. Most new air-induction nozzles are only available in 110 degrees. Another reason why Klein favors a 30-inch nozzle spacing is that most farmers are still planting 30-inch rows. "So if we want to use drop nozzles, we can just add extensions to have drop nozzles," Klein said.
Thirty-inch nozzle spacing also allows for 50 percent larger nozzles. That, in turn, provides for using lower application rates without going to extremely small nozzles. Klein likes to avoid nozzles that require less than a 50-mesh nozzle screen because smaller screens tend to plug.
The third thing determining application rate is the nozzle flow rate, made up of nozzle orifice size, pressure and solution density. "Remember that anything heavier than water comes out more slowly than water, so we need to adjust the sprayer to compensate," Klein said.
He listed two concerns in sprayer calibration: efficacy and drift.
In his work, Klein has gotten good results from the new air-induction nozzles. Most older air induction nozzles required pressure of about 50 pounds per square inch, but the new extended-range air-induction nozzles are best set at 30 psi.
West Central REC, North Platte