Department of Soil&Crop Sciences

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Calibrating a Drop Spreader

Measure the width of the drop spreader pattern and lay out and mark a calibration distance

We will be using the sweep-up method first in this calibration exercise - followed by the catch pan method.

Start by familiarizing yourself with your drop spreader - what is the width of the drop pattern? Lay out a calibration distance on a smooth clean floor (10 feet is usually adequate). Mark your calibration distance with objects or paint and follow these steps.

You will need a few things before beginning this process:

  • Measuring tape
  • Accurate scale
  • A cup or tray to hold fertilizer pellets
  • Broom and dust pan
  • calculator
  • Know your desired application rate
  • Have your desired fertilizer

You will need to know your desired application rate and the analysis of your fertilizer product before you begin this process.

Example: You want to put down one pound of nitrogen per thousand square feet of a fertilizer with the analysis of 21-0-0 (21% nitrogen).

To determine how much of this particular FERTILIZER per thousand square feet you need to equate to one pound of nitogen per thousand square feet - divide the desired RATE by the ANALYSIS.

1 pound N per thousand / 0.21 (21%nitrogen)
1/0.21 = 4.76 pounds of this particular fertilizer
This means that you need to spread 4.76 pounds of this fertilizer over 1000 square to put out the desired 1 pound of nitrogen per thousand square feet.

Now determine how much of this fertilizer you need to drop within the calibration distance to properly calibrate your spreader.

You need 4.76 pounds of 21-0-0 for 1000 square feet - now determine your calibration area.
You have for example a spreader that is three feet wide and a calibration distance of 10 feet. 3ft x 10ft = 30 square feet

4.76 pounds of 21-0-0 X pounds of 21-0-0
1000 square feet 30 square feet

cross multiply (4.76)(30)=(1000)(x pounds)
x = 0.14 pounds of 21-0-0 in the calibration area - this is equal to 2.3 ounces (16 ounces per pound) and 65 grams (454 grams per pound).

Now you go through the calibration process with the ultimate goal of finding the correct setting on the spreader to drop this amount of fertilizer within the calibration area.

Designed by Jason L. Gray.