Calibrating a boom sprayer, Ozkan said, is not as difficult as it sounds. It usually doesn’t take more than 30 minutes, and only three things are needed: a watch showing seconds, a measuring tape, and a jar that measures ounces. The ultimate goal is to calculate the actual rate of application in gallons per acre to check for accuracy, or to make adjustments as needed.

Ozkan recommends a method based on spraying 1/128 of an acre per nozzle and collecting the amount of chemical that would be released during the time it takes to spray that area. This particular amount of land is chosen because there are 128 ounces of liquid in one gallon, making it easy to correlate the number of ounces sprayed on that small area to the number of gallons that would be sprayed on the whole acre. For example, if you catch 15 ounces from a set of nozzles, the actual application rate of the sprayer is equal to 15 gallons per acre.

For this method to be accurate, it is important to make sure that the time used to collect the spray from the nozzles is the same that it takes to cover 1/128 of an acre. A table available at http://ohioline.osu.edu/aex-fact/0520.html shows various nozzle and row spacings and the time you must travel to cover 1/128 of an acre for each spacing. For example, the travel distance for a 15-inch nozzle or row spacing is 272 feet; for a 20-inch nozzle or row spacing is 204 feet; and for a 30-inch nozzle or row spacing, the distance is 136 feet.

To calibrate a boom sprayer for broadcast applications using this method, follow these steps:

1. Fill the sprayer tank with water.

2. Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.

3. Measure the distance in inches between the nozzles. Then measure an appropriate distance in the field based on this nozzle spacing, according to the table available at http://ohioline.osu.edu/aex-fact/0520.html.

4. Drive the measured distance in the field at your normal spraying speed, and record the travel time in seconds. Repeat this procedure and average the two measurements.

5. With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in step 4.

6. Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. If an individual sample collected is more than 10 percent higher or lower than the average nozzle output rate, check for clogs and clean the tip, or replace the nozzle.

7. Repeat steps 5 and 6 until the variation in discharge rate for all nozzles is within 10 percent of the average.

8. The final average output in ounces you get is equal to the application rate in gallons per acre.

9. Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments.