Application Equipment, Calibration, and Techniques
What calibration answers
Calibration determines gallons per acre delivered. Three variables control it - nozzle flow, ground speed, and swath width - and changing any one changes the rate. Pressure and flow are related by a square-root rule: quadrupling pressure doubles flow.
Nozzle flow formula
GPM per nozzle = (GPA x MPH x nozzle spacing in inches) / 5940. With 20 GPA, 10 MPH, and 20-inch spacing: (20 x 10 x 20) / 5940 = 0.67 GPM. Choose the nozzle size closest to that flow at your intended pressure.
The 1/128 acre method
One hundred twenty-eighth of an acre is 340 square feet. Mark a course so that nozzle spacing times course length equals 340 square feet: at 20-inch (1.67 ft) spacing, the course is 340 / 1.67 = 204 feet. Drive it at field speed, catch one nozzle's output in ounces, and ounces collected equals gallons per acre. Verify speed with MPH = (feet x 60) / (seconds x 88).
Nozzles and pattern
Check the pattern with a spray card or in a tray; replace nozzles worn more than 10 percent above rated flow, and replace all nozzles as a set. Higher pressure means finer droplets and more drift; wider fan angles require lower boom height.
Techniques
Match carrier volume to the product and target, keep the boom level and at the labeled height, avoid overlaps at headlands, and rinse the system between products. Trap: calibrating once a season - recalibrate when nozzles, speed, or formulation changes.
Traps
- Mixing units (ounces, gallons, inches).
- Assuming gauge pressure equals nozzle pressure when screens or filters are plugged.