Spreader Calibration

Adapted with permission from the Rittenhouse fertilizer calibration manual

The approximate spreader settings printed on any product label should only be used as the initial setting for calibration. Set the rate control arm at this approximate setting.

Two items must be considered when calibrating a spreader. The first is the distribution pattern of the spreader. That is, the pattern the product makes as it strikes the ground after being thrown out by the spreader’s impeller. The second item is the product application rate, which is the amount of product applied per thousand square feet.

The product application rate, which is the amount of product applied per thousand square feet, is also significant because over-application can be costly and may cause plant injury, while under-application will reduce the effectiveness of the product.

To Calibrate A Spreader, Follow These Steps:

First make sure the spreader discharge holes are not fully closed. Second thread the upper jam nut on the operating lever rod further up the rod. Next, tighten the lower locknut and recheck. Repeat this procedure until the holes are fully closed.

To Achieve A Uniform Distribution Pattern:

The accurate method for checking pattern uniformity is to lay out shallow boxes or pans in a row on a line perpendicular to the direction of spreader travel. Eleven boxes or pans, two inches high placed on one-foot centers will provide accurate calibration. To conduct the test, begin with the pattern slide completely open and set the rate control arm at the suggested approximate setting. Make three passes over the boxes, pushing the spreader in the same direction each time. The product caught in each box is then evaluated to determine the distribution pattern. Weighing the product in each box is the most accurate, but a simpler method is to pour the contents of each box into a separate small vial or bottle. Then set the eleven vials or bottles side-by-side in order. This makes the pattern variation quite visible.

To reduce the amount of discharge to the right side (operator’s right) the pattern slide should be partially closed and the test repeated until the distribution pattern is uniform.

To Achieve The Correct Product Application Rate:

Using the collection of boxes or pans, make a single pass over them to determine the effective pattern width. The effective pattern width is twice (2x) the distance to the point where the rate drops to one-half the average rate at the center. Example: If the product in the vials from the center boxes averages two inches in depth, count out to the vial that has one inch of product. If this is the fifth vial from the center and the boxes were on one-foot centres, the effective pattern width is ten feet. (2×5 ft.)

The LESCO Calibration Gauges provide a series of “steps”, numbered in 1/32-inch increments, which will allow you to fine-tune the LESCO spreader. Once you have calibrated your rotary spreader for the product chosen, open the operating lever and insert the calibration gauges until you determine which step fits tightly into one of the open holes in the hopper bottom. Record that step number for future reference when using that product. You may choose to set other rotary spreaders for application of the same product by adjusting the shutoff plate to that calibration gauge step. This will provide consistent settings for all of your spreaders.

Fertilizer Spreader Tips:

1. Always push the spreader; do not pull.
2. Push the spreader at a consistent speed (approximately 3 m.p.h. is recommended)
3. Always close the operating lever before filling the hopper.
4. Be sure the screen is in place to prevent lumps or paper scraps from plugging the holes in the hopper bottom.
5. Always start walking forward before opening the operating lever, close the operating lever before forward motion is stopped.
6. Hold the handle at a height that will keep the impeller level.
7. Empty the spreader after each use. Wash the spreader thoroughly and allow it to dry. Keep the impeller clean.
8. Lubricate all moving parts. Apply grease to the five grease fittings: two in the axle supports, two in the gear support and one in the idler wheel (if the idler wheel has a steel hub.)