Application Equipment, Calibration, and Techniques
Nozzles and droplet size
Flat-fan nozzles give a tapered or even pattern for broadcast spraying; hollow cones make finer droplets for penetration and directed work; full cones handle soil and band work; air-induction and flooding tips produce coarser droplets and reduce drift. Droplet size drives the tradeoff: finer droplets cover better but drift farther.
The calibration formula
The standard relationship is gallons per acre = (GPM per nozzle x 5940) divided by (MPH x nozzle spacing in inches). Flow varies with the square root of pressure, so doubling pressure raises flow only about 41 percent while making droplets smaller and driftier. Doubling ground speed halves the gallons per acre.
Worked example
An 8002 nozzle delivers 0.2 GPM at 40 psi, on 20-inch spacing, at 4 MPH. GPA = (0.2 x 5940) divided by (4 x 20) = 1188 divided by 80 = 14.85 GPA. To apply 15 GPA, hold those settings; to change rate, change speed, pressure, or nozzle size rather than guessing.
Calibration discipline
Measure a known area, catch from several nozzles, confirm all are within about 5 to 10 percent of the average, and recalibrate after nozzle changes. Nozzle wear enlarges the orifice, raising flow and skewing the pattern.
Drift management
Use lower pressure, coarser nozzles, lower boom height, shields, and appropriate wind conditions. Spraying during a temperature inversion, or in wind above the label limit, is a frequent trap.