Calibration How Tos: How to Calibrate Your Rotary Spreader
rotary spreaders are an effective tool in turf and ornamentals management both on the commercial and consumer levels and with proper calibration the spreader will prevent overdosing or under dosing conditions which could lead to excessive product application, lack of pest control, damage plants, or even costly fines nursery workers, landscapers, and homeowners need to know the simple calibration processes and basic math in order to have accurate dispensing and materials will be performing the calibration and a simple scaled-down version so that you can use proportions to match your situation the first thing you need to do is determine the effective swath width in other words how wide is the path that your material was being evenly spread an easy way to do this is to spread out in odd number of catch trays or pans at two foot intervals this collection pan should all be the same size 1 or 2 inches deep and with an area of at least 1 square foot most pie pans don't meet this last specification better used in this program for demonstration purposes only box lids are preferable. also, be certain to take all necessary precautions for personal protection. unlike calibrating spray equipment you need to use the actual product pesticide or fertilizer granule when conducting a spreader calibration. run the spreader with the gate open over the top of the center pan in a perpendicular manner you may need to do this several times to get a good representation sample make sure you approach the pans from the same direction each time, then using a funnel, gather all the material from each individual pain into a series of jars or even the individual segments of a large size pillbox obviously this pill box must never be used for anything other than pesticides you should be able to see the pattern with the center pan catching the most and each subsequent pan to either side tapering off evenly look for the pans that have captured half as much as the center and this represents your affective swath once you know the distance between the pans either end up the swath you'll be able to determine the effective width in this case 8 feet because it's difficult to produce a completely even spread with rotary spreaders it's usually best to make 2 passes over a treatment area therefore, we'll base the calibration on applying half the products listed label rate calibrating to the full label rate in making 2 passes on an application would lead to a double dose a product weigh out enough product to load the spreader for a calibration test over a distance of 1000 square feet with a swath with the 8 feet our calibration distant should be 125 feet 1000 divided by 8 equals 125 due to the limitations of space our test will take place over a course measured at 62.5 feet will conduct one pass with the gate open, close the gate to turn around, then make another pass to our starting point for a total of 125 feet. now take and weigh the remaining portion of the material that is left from the spreader subtracting that total from the starting weight will give you the application rate for 1000 square feet remember because we're making two passes an application our total should only be half of the desired label rate give or take 10 percent. let's look at an example you want to calibrate your rotary spreader to apply insecticides granules at the labeled rate up three pounds per 1,000 square feet because you'll calibrate the spreader to deliver one-half of the labeled rate your goal is to apply 1.5 pounds per 1000 square feet. with an effective swath width 8 feet you'll need to travel 125 feet to accomplish your calibration test area above 1000 square feet. you decide to put 4 pounds a product into the spreader before the test and after running the test course the remaining product weighs 1.5 pounds the calibration application rate is therefore 2.5 pounds per 1000 square feet adjust the spreader by reducing the gate opening and performing another calibration test until the rate falls within the desired rate in this case that would be roughly 1.4 to 1.7 pounds while this may require multiple calibration tests the results are essential to proper dispensing in materials if the label states a target application rate per acre multiply the amount from the 1000 foot calibration course by 43.56 to arrive at your per acre rate. for example, if the herbicide you're going to apply calls for label rate up 80 pounds per acre and the calibration application rate is 2.5 pounds per 1000 square feet as previously measured then you're calibrated output is 108.9 pounds per acre this amount far exceeds the 40 pounds per acre goal so the spreader gate opening will need to be reduced accordingly and the spreader recalibrated. after the rotary spreader is properly calibrated to the desired label application rate there are two ways to make the application the first is the right angle method.
space your passes at the effective swath width covering the area properly, then make a second series of passes also at the effective swath width but at a right angle or perpendicular center passes to the original series.
the second method for application would be the half-width method use parallel passes at half the measured swath width for example in our calibration we determine the spreader to have an eight-foot swath for the half with method each pass but only be separated by 4 feet remember that consistency is the key your calibration results are only appropriate for the product that you're applying as well as the speed of travel and the height at which you hold the spreader handles at first calibration over rotary spreader may seem complicated however, as you can see when you apply the proper materials that the correct rate you not only have great results but you'll save time and money too