Calibrate Spreaders to Improve Manure Applications

November 9, 2013 03:23 AM
Calibrate Spreaders to Improve Manure Applications

Consistency probably isn’t the first word you think of when you consider how to improve manure applications on your fields. But getting an even amount on every acre is one of the primary challenges farmers face when using manure as a crop nutrient, says Isaac Ferrie, a certified crop adviser with Crop-Tech Consulting.

"Poor distribution of manure across the field can result in uneven crop growth," Ferrie notes.

He says the best way to achieve a consistent application is to calibrate your spreader equipment,
a practice used by only one-third of farmers who apply manure, accor­ding to surveys conducted by Ohio State University Extension. Yet, calibrating equipment takes only an hour or so. That time, plus a little effort, can save you a bundle of cash.

A simple task. There are two common calibration methods—the weight method and the flow method. Ferrie says both methods work well, depending on your particular machinery setup and preference.

With the weight cali­bra­tion method, you have a couple of options. You can weigh the manure spreader before and after application, or you can install load cells on the spreader, much like you would with a grain cart to weigh corn.

If you apply liquid manure, you might want to consider using the flow method. It requires using a large electromagnetic flow meter (the 3" size or larger) to measure the actual flow of product through the machine. This process is like sidedressing liquid nitrogen using variable-rate technology. One major difference is that the electromagnetic flow meter for manure has no moving parts in the meter.

For both calibration methods, you need to know your swath width. This will help you determine how far apart to make each pass in the field so the manure is evenly dispersed.

The tarp test is the easiest way to accomplish this. Evenly space a series of three or four 56"-square tarps in a straight line in the field. Drive the spreader over the set of tarps, making sure your speed is equivalent to what you would normally run. Next, weigh the product that lands on each tarp.

"Fold up the tarp and set it on a scale," Ferrie says "You should only have 8 lb. to 10 lb. of manure on each tarp if you’re spreading 8 tons to 10 tons of manure on the field."

That’s because the calculations are set so that every 1 lb. of manure that lands on a tarp is equal to 1 ton of manure per acre. By analyzing the amount of manure on each tarp, you can determine how even your application rate is across the field and make adjustments to your swath width.

As you evaluate swath width, it’s helpful to understand that the distribution from a spreader typically resembles a triangle with the maximum application rate near the spreader path and decreasing rates further from the spreader path, explains John Worley, University of Georgia Extension poultry specialist.

"When the spreader pattern looks like this, the edge of the effective swath width occurs at the point where the application rate is one-half the maximum rate," Worley says. "If the rate is 4 tons per acre in the middle and decreases to 2 tons per acre 20' to the side of the spreader, then 20' is the edge of the effective swath. Since this occurs on both sides of the spreader, the effective swath width is 40'."

Worley says some application overlap is necessary to even out the distribution: "If the spreader paths are 40' apart, the overlapping patterns will produce a uniform application rate of 4 tons per acre."

You can e-mail Rhonda Brooks at

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