Calibrating Solid Manure Application Equipment

Why should you calibrate solid manure spreaders? Simple, because you should know how much manure was applied to your fields. Combined with a manure testing program, you can calculate the amount of manure nutrients that were applied. This can save money on commercial fertilizer purchases AND improve water quality. Related: Calibrating liquid manure spreaders and irrigation equipment.

What Can Cause Manure Application Rates to Change?

Solid spreaders can have poor uniformity if operated improperly, so proper operation and calibration of these types of systems are critical. The system needs to be recalibrated if any of the following are changed:

  • Tractor speed
  • Gate opening (and spinner settings for spinner spreaders)
  • RPM
  • Width of spread
  • Manure characteristics
  • Wind
  • Slope
  • Operator (experience and consistency)

It is helpful to know the capacity and setting ranges available with solid spreaders. Solid spreader capacity is noted in the manufacturer’s specifications and may be listed in tons, cubic feet or cubic yards. Capacity is normally listed in struck level (flush with top of unit) height but may also be rated in “heaped” load.

This video shows how tarps that are laid out and manure spread on them can be collected and weighed. it was produced with smaller farms in mind, but the concepts and procedures apply to equipment of all sizes. Produced by: Rutgers University Cooperative Extension.

What Are the Steps in Calibrating Solid Manure Spreaders?

This video shows a process for weighing the  manure spreader and measuring the area over which manure was applied. The worksheet referenced is Know How Much You Haul Produced by the University of Wisconsin Cooperative Extension.

Tarp Method

Normally calibration of solid spreaders will involve collecting the discharged manure in a tarp to determine application rate and collecting manure in a series of pans laid across the travel path to assess spread pattern, uniformity and to adjust pass width. Click on the following link for an illustration of the procedure for this method. (Source: Rick Koeslch, University of Nebraska). Manure density is normally determined to allow conversion from volume to weight (e.g. tons) applied.

Weighing the Spreader

If manure spreader capacity can be weighed, then the only field measurements required are distance traveled to empty the spreader and width of spread pattern (or distance you move laterally with each pass through the field). From that information, a fairly simple estimate of application rate can be made.

Moisture content of manure has a large impact on manure density and actual spreader capacity. When calibrating, it is important to correctly interpret the nutrient analysis reports provided by the analytical lab. Some analyses report manure nutrient concentration at the moisture content submitted. Other analysis reports may give the nutrient analysis at a moisture content that is different than either the sampled material or the material to be applied. For accurate calibration, match moisture content of manure samples with moisture content of the manure being spread.

Adjustments to achieve the proper application rate and uniformity include adjusting travel speed, gate openings and hammer clearance, and adjusting spinners for spinner spreaders. Narrowing the effective width (pass distance) generally increases application uniformity but also increases application rate.

Types of Solid Manure Application Equipment

Manure is generally handled as a solid at a solids content of 20% or more. Solid manure spreaders come in various types. Spinner spreaders use spinning disks at the rear of the unit to propel the manure, box spreaders use a paddle and/or auger to discharge manure from the rear of the unit, and side discharge spreaders typically use augers and flailing hammers to “throw” the manure out the side of the unit. Spinner spreaders are used to apply poultry litter and are widely used as commercial fertilizer applicators. Side discharge units can handle materials with a wide range of moisture contents. Rear discharge spreaders are commonly used with scraped manure solids from open lots and manures with significant bedding.

Recommended Educational Resources

Author: Garry Grabow, North Carolina State University
Reviewers: Marsha Mathews, University of California-Davis, Rick Koelsch, University of Nebraska, Doug Beegle, Pennsylvania State University