Boom sprayer calibration tips
Calibrating a row crop sprayer with two or three nozzles per row (Figure 3) is similar to calibrating a band sprayer. With broadcast or band applications, GPA is equal to the output from one nozzle. When more than one nozzle is used per row, the combined amount collected from all nozzles directed at one row is equal to the GPA. Again, this application rate is not the same as the broadcast rate. You must convert the recommended broadcast rate to the band rate before comparing it with the actual rate you obtained with calibration.
You want to spray a 30-inch row using three nozzles per row. The steps:
- Select a travel distance from Table 1 based on row spacing. The distance to travel for a 30 inch row is 136 feet.
- Drive 136 feet and measure the time in seconds.
- If it took 15 seconds, catch the output from each of the three nozzles for 15 seconds. If each tip delivers 5 ounces, the total ounces collected per row is 15 ounces. This represents the sprayer application rate of 15 GPA. (5 ounces/nozzle X three nozzle/row = 15 ounces/row).
- Repeat Step 3 for each set of nozzles on the boom to make sure the application rate is uniform across the boom.
Adding the Chemical to the Tank
You can spend hours in the field to achieve the accuracy desired from your sprayer through proper calibration, but it won't do any good if you don't know how much chemical to put in the tank. A survey conducted by agricultural engineers at the University of Nebraska revealed that of the applicators surveyed, 38 percent failed to add the correct amount of chemical to the tank.
The amount of chemical needed per tankful depends on the recommended rate and the number of acres you can treat per tank of spray.
- To find the acres treated per tank, divide the tank capacity by the GPA application rate.
- To find the amount of pesticide needed per tank, multiply the number of acres treated by the amount of actual chemical to be applied per acre.
Example 1 (broadcast application)
A sprayer has a 300 gallon tank, and it has been calibrated to apply 15 gallons per acre. The pesticide label recommends 2 pints of commercial product per acre for broadcast application. Determine the quantity of pesticide to add to the tank:
- First, find the acres each tank will spray: 300 gal. per tank/15 gal. per A. = 20 A./tank
- Next, calculate the number of pints to be added to the tank:
20 A./tank X 2 pts./A. = 40 pts./tank
- The final mix consists of 40 pints (5 gallons) of pesticide formulation and 295 gallons of water per 300 gallons of tankful.