3/1/2022 - By Dr. Jeff Atkinson

Optimum product performance is a result of a quality product applied with accurately calibrated equipment by a skilled applicator. These four tips will help ensure your investment in quality products translates into optimum performance.

Start the calibration process with Harrell’s Spreader Calculator.

Harrell’s Spreader Calculator considers granule size, spreader model, walking speed, blend bulk density, and target application rate to provide a starting point for calibration. While reasonably accurate, all spreaders are slightly different, so it is a good idea to field test spreader calibration prior to product application to managed turf areas. Harrell’s Spreader Calculator can be found here: Harrell's Spreader Calculator

Use calibration gauges to uniformly calibrate multiple spreaders.

While each spreader brand is unique, fertilizer flow rate is generally set by adjusting a restriction plant on the rear of a hopper by referencing a set of letters or numbers. For example, Harrell’s Spreader Calculator indicates a mini sized blend with a 45 lb per ft3 bulk density applied at 5 pounds of product per 1000 ft2 should be applied using setting 25 on a Lesco Rotary Spreader. This assumes the spreader is calibrated to factory specifications. Over time, spreader settings are bumped out of factory specifications. Normal wear and tear, incorrect assembly, or mishandling during transportation are all contributing factors.

As an alternative, use of a calibration gauge is a repeatable, accurate way to ensure spreader port holes are calibrated to open to the correct size and position uniformly across multiple spreaders (Figure 1). 

Figure 1 . Calibration gauges are useful tools to ensure uniform calibration between multiple spreaders.

Assign each applicator a spreader.

Some applicators walk slow, some applicators walk fast. Since walking speed has a direct effect on product application rate it is important to ensure each spreader is calibrated for each applicator’s walking speed. Considering the differences amongst spreaders outlined in point 2, an applicator using a different spreader from application to application will likely result in variability in application rate. Assigning each applicator a spreader removes this source of variability, resulting in more consistent applications.

Regularly clean and service spreaders.

Through a single application or a full season, granular spreaders experience a lot of wear and tear. As an example, residues from granular materials can accumulate on spreader impellers which affects application accuracy and uniformity (Figure 2). Service all parts per manufacturer recommendations to ensure proper spreader function throughout the season. The adage an ounce of prevention is worth a pound of cure certainly applies to spreader maintenance.

Figure 2 . Accumulation of fertilizer blend residues on an impeller blade will negatively impact spread accuracy and uniformity.

Growing season is right around the corner. A relatively small amount of time preparation for the season by calibrating and tuning up application equipment will ensure you maximize your investment in quality products. If you have questions about calibration reach out to your Harrell’s rep, they are experienced and ready to help you get the most out of your program this season.