Boom sprayer calibration tips
Calibrating for Band Spraying
Pesticides sometimes are applied in bands centered on the crop row (Figure 2). The application rate on the treated band must be the same as the broadcast rate for band application to be effective. But the total amount of pesticide used on a field is less, because only a portion of it is treated with chemicals.
Figure 2. Band spraying. Calibrating a sprayer for banding applications is similar to the procedure outlined for broadcast sprayers. The only difference is to choose the travel distance from Table 1 based on row spacing, not nozzle spacing. Drive the distance shown in the table at your spraying speed and catch the output from each nozzle for the length of time it takes to travel the indicated distance.
The average nozzle output again is directly equal to the application rate in gallons per acre. This application rate is less than the broadcast rate, because only a portion of the field is treated with chemicals. For example: If the broadcast rate recommended is 15 GPA and you're spraying 10-inch bands on 30-inch rows, you will need only 5 GPA, one-third of the broadcast rate. Therefore, at the end of your calibration, the average number of ounces caught from all the nozzles should equal 5 ounces, which represents an application rate of 5 GPA. At this rate you will treat bands at the recommended 15 GPA rate but the entire field at 5 GPA.
Herbicide recommendations are usually given on a broadcast basis. Therefore, convert the recommended broadcast rate to the band rate before comparing it with the measured rate to determine the application error. To convert a broadcast application rate to a band rate, use this formula:
Band rate = Band Width (in)/Row Spacing (in) X Broadcast rate
Then, compare this converted band rate to the measured rate. Make some adjustments and recalibrate the sprayer if the difference between the two rates is greater than �5 percent of the recommended rate.
- Recommended broadcast rate: 15 GPA
- Rate measured with calibration: 6 GPA
- Row spacing: 30 inches
- Band width: 10 inches
Determine the sprayer application error:
First, convert the recommended broadcast rate of 15 GPA to the band rate:
10-in. band width/30-in row spacing X 15 GPA = 5 GPA
Application error = 6 GPA - 5 GPA = 1 GPA (off by 20%)
Because the application error is more than 5 percent of the recommended rate, adjustments must be made and the sprayer must be recalibrated.
Figure 3. Directed spraying. Calibrating for Directed Spraying
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