Briefly describe how to calibrate a rotary spreader.

• A. Load a known weight, apply to 1,000 square feet, weigh remaining product, adjust gate to achieve within 10% of the labeled rate, repeat
• B. Pour product until the spreader feels full, then apply to field
• C. Estimate by eye on 1,000 square feet and compare to a chart
• D. Calibrate by spraying into water and measuring concentration

Answer: (A)

Calibrating a rotary spreader is about ensuring the actual amount of product released over a defined area matches the label’s rate. The reliable way is to use a known quantity of product and spread it over a defined area, typically 1,000 square feet. Load the spreader with a measured amount, apply it to the area, then weigh the remaining product to determine how much was actually used. From that, calculate the application rate (amount used per 1,000 ft²) and compare it to the labeled rate. Adjust the gate until the rate is within the label’s tolerance, usually within 10%. Repeat to confirm consistency under the same conditions.

This method directly measures what is being applied, accounting for gate setting, speed, and material density, so you can achieve a repeatable, accurate rate. Estimating by eye, filling until the spreader feels full, or testing in water and assuming the concentration will translate to dry granular distribution don’t provide an accurate or reliable measure of the field rate.