Sunday, July 06, 2008

NORTH PLATTE, Neb. --  If producers don’t have even pressure throughout the sprayer boom, they won’t get even application of chemicals, 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. But it’s important to check pressure all along the boom first because there might be a restriction in the line.

Klein advised checking 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 sprayers 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.”

There are three basic things that 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 30-inch nozzle spacing is just as effective, if the producer uses 110 degree nozzles. Most of the new air-induction nozzles are coming out with 30-inch spacing, Klein said. The other thing Klein likes about 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 extenders and easily put on 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 that determines application rate is the nozzle flow rate, made up of nozzle orifice, 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.

One new nozzle type that does well in Klein’s work is the air-induction type. Most of the old air induction nozzles required pressure of about 50 pounds per square inch.

The new extended-range air-induction nozzles, however, are best set up at 30 psi. So a lot of producers may want to investigate the new extended-range air-induction nozzles.