| | Figure 1. Four samples of Scott "Standard" spreaders compared for rate consistency. |
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| | Figure 2. Four samples of Vigoro "10,000" spreaders compared for rate consistency. |
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| | Figure 3. Rate variation among four samples of each spreader model using a low rate of turf fertilizer. |
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The spreader settings typically found on bags of fertilizer and granular pesticides are usually based on tests performed on one sample of each spreader model listed. This procedure assumes that all spreaders of that model are identical and will thus require the same spreader settings. Unfortunately, that is not often the case – at least with homeowner spreaders.
Most true professional spreaders are reasonably consistent from one sample to another and can be recalibrated by the user to assure that they deliver consistent rates. Most homeowner spreaders cannot be recalibrated by the owner and are not consistent from one spreader to another of the same model.
A study conducted by the LSU AgCenter looked at four supposedly identical spreaders of each of two brands purchased from local stores. Spreader settings were developed using one spreader of each model, then the other three spreaders of that model were tested using those settings to see if they delivered the same rate. They did not. With the worst of the two brands, one sample spreader delivered over four times the rate of another supposedly identical spreader at the same setting using a low rate of fertilizer. The distribution pattern also varied among supposedly identical spreader models. Variations across the distribution pattern add to the variations in delivery rate so that the actual rate applied to a given area of the lawn can vary greatly.
This means that a spreader owner who follows the spreader setting recommendation on the label exactly could end up applying over four times as much fertilizer or pesticide as the recommended rate if one of the less consistent spreader models is used.
Even the better spreader samples tested had significant differences in rate, but the highest delivery rate was less than twice the lowest rate with that model.
About all a homeowner can do to minimize this problem is to buy one of the better spreader models, check the coverage actually delivered to his/her lawn by comparing the area covered with the recommended coverage for that bag of product and then correct the setting slightly if needed the next time the spreader is used. If you use a less consistent spreader model, the rate setting on the product label is unlikely to deliver the expected rate in your spreader.