Calibration, Worn Nozzles, and an Aquatic Buffer
An applicator is calibrating a 300-gallon boom sprayer before treating a 60-acre field of dry peas. The boom has 11003 flat-fan nozzles spaced 20 inches apart; the target is 15 GPA at 5 mph and 35 psi. A timed catch from several nozzles over 60 seconds averages 0.33 gal per nozzle, and one nozzle delivers 0.38 gal. The label requires a 100-foot downwind buffer next to aquatic habitat, and an irrigation ditch runs along the field 75 feet from the boom's edge. Wind is 12 mph gusting to 20, blowing toward the ditch. It is 7:30 a.m., and the forecast calls for the wind to shift by 2 p.m. A farmstead well is 0.25 mile from the field.
1. Calculate actual GPA and acres per tank, and decide what to do about the output.
Read the worked answer
Actual output GPA = 5,940 × GPM ÷ (mph × nozzle spacing in inches) GPA = 5,940 × 0.33 ÷ (5 × 20) = 1,960 ÷ 100 = 19.6 GPA
This is about 31% above the 15 GPA target. The target flow per nozzle is: GPM = 15 × 5 × 20 ÷ 5,940 = 0.2525 gal/min
Acres per tank at current output 300 gal ÷ 19.6 GPA = 15.3 acres per tank
Decision
- The average nozzle is far above target, and the 0.38 gal nozzle is worse. This pattern indicates worn nozzles, not a pressure problem.
- Replace nozzles delivering more than about 10% above the rated flow, then recalibrate the whole boom.
- Do not compensate by changing speed or pressure alone; pressure changes flow only with the square root, and worn tips distort pattern.
- Check the pressure gauge and all screens while recalibrating.
2. Given the buffer and wind, should the application proceed this morning? Explain.
Read the worked answer
No. Three independent reasons point to waiting:
- Buffer distance: the label requires 100 feet downwind of aquatic habitat. The ditch is only 75 feet away and the wind is blowing toward it, so the required setback cannot be met.
- Wind speed: 12 mph gusting to 20 is likely above the label's maximum wind condition and is certainly high-risk for drift.
- Sensitive receptor: an irrigation ditch is aquatic habitat and may carry water to other properties.
The wind shift forecast for 2 p.m. does not justify spraying now. Wait for the shift, recheck the actual wind at the boom, confirm the buffer is met, and consider low-drift nozzles and a vegetative setback. If conditions do not improve, do not spray.
3. List the environmental protection steps you would take for this field, including the well and the ditch.
Read the worked answer
- Buffer: leave an unsprayed vegetative strip wider than the label minimum along the ditch, and do not treat the ditch bank.
- Drift reduction: use low-drift nozzles, lower boom height, and spray only when wind is within label limits and away from the ditch.
- Mixing and loading: do this well away from the well and the ditch, on a pad or contained area, with an anti-backflow device on the water supply.
- Well protection: keep the mixing site and rinse water away from the wellhead; check the label and local setbacks, and never dump rinsate near the well.
- Rinsate: triple-rinse containers and apply rinsate to the labeled field at the labeled rate; do not dump it on the ground or into the ditch.
- Spill kit: keep absorbent material and a tarp at the mixing site.
- Records: note wind, buffer distance, and the decision to wait, so the judgment call is documented.