Pictorial Guide to Calibrating Poultry Litter Spreaders

The use of poultry litter as a crop fertilizer is economically and environmentally important in Alabama. To be used effectively as a fertilizer, poultry litter must be applied evenly and at the proper rate.

In order to get the most out of the litter, the farmer must:

Know the crop's fertilizer needs
Know the fertilizer value of the litter
Put the right amount of litter on the land
Uniformly apply the litter

A crop or pasture's fertilizer needs can be obtained from county extension offices. Most dry poultry litter in Alabama has about 3% nitrogen, 3% phosphorus, and 2% potassium. It can be considered a 3-3-2 fertilizer.

Many farmers do not know exactly how much litter they are applying or how uniformly it is being applied to their land. There are many variables to consider--truck speed, PTO rpm, gear box setting, discharge opening, width of spread, and overlap pattern. By calibrating the spreader truck, farmers and certified animal waste vendors can apply poultry litter uniformly to the land at the best rate.

Measuring Rate of Application

Items needed to calibrate spreader truck:

5 Gallon Bucket
Tarp (8 ft by 8 ft, 10 ft. by 10 ft., 9 ft. by 12 ft., or 10 ft. by 12 ft.)
Scales (10-20 lb. capacity hanging scales work well)

To measure the rate of application of dry litter:

Weigh bucket empty to determine the empty weight
Locate a large, reasonably smooth, flat area where litter can be applied
Spread tarp on the ground. It's usually necessary to use pins or weights to keep wind from moving the tarp.
Drive spreader truck at normal application speed, allowing the litter to begin leaving the spreader at a normal rate well before reaching the tarp.
Gather up tarp so that none of the litter is lost. Carefully transfer the litter to the weigh bucket.
Weigh bucket with litter
Subtract the empty weight of the bucket to determine the weight of the litter applied to the tarp.
Use the following equation to determine the litter application per acre:

Pounds of litter collected over ground cover X 21.78 = Tons/Acre
Area of ground cover (sq.ft)

Note that many plastic tarps are measured by the pre-finished size. After finishing the edges of the tarp, it may be significantly smaller than listed on the package. Measure actual size to be sure.

Determining Uniformity of Application

Uneven litter application will cause uneven growth of the crop. If the path of the spreader truck can be seen, as it can be in this photo, then the application was likely done very poorly. Large differences in application rate are necessary to produce such patterns. Litter is almost always spread more heavily near the spinners and more thinly toward outer limits of the spreader's reach. Most spreaders will have only small amounts of litter spread further than 18 feet from the trucks path.

Items needed to check the uniformity of spread include:

small scales that can measure grams or ounces (optional)
plastic pans of equal size such as dishpans
wire flags to mark location of pans

Uniformity or evenness of the spreader's pattern can be tested at the same time that the rate of application is tested. To test for uniformity, place pans across the width of the spreader path. Eleven pans of equal size spaced at three foot intervals (omitting two pans where the truck tires will pass). Place the center pan in line with the center of the ground cover. Place a flag at each pan to save time placing pans for additional runs.

	The distribution pattern from one pass should look like the one pictured here. The litter will be placed heaviest in the center and taper off evenly on both sides. The overlap of each spreader pass results in an even pattern.
	If the spreader passes are too far apart a uneven pattern will result.

The driver should drive one pass to the left of the test field, one pass over the center, and one pass to the right of the test field. The passes should be the same distance apart that is normally used during spreader operation. After making the three passes over the test field, compare the amount of litter in the pans. A visual inspection will provide some information about the spreader pattern. Weighing the contents of each pan on a small scale will provide a more accurate estimate. Plot the amount of litter in each pan on a graph. Click here for a printable blank graph.

If the distribution is not uniform, then adjust either the spreader's swath width or the distance between spreader passes. Adjust the distance between passes to increase or decrease the overlap.

It's also possible to adjust the location of the deflector, which determines the where the litter will be deposited on the spinners. If the deflector is moved toward the front of the spreader truck, more litter will fall on the center of the spinners; move the deflector toward the back of the spreader and more litter will fall on the edges of the spinner. Making this adjustment will take some trial and error before getting a good pattern. Also, check the condition of the spreader fins. Missing or bent fins will reduce the spreaders swath.

Setting flags to mark the location of pans. The flags are set at 0,6,9,12,15, and 18 feet from the trucks path.

Inexpensive plastic tarp spread on the ground. Tarp has to be weighted or staked down.

Completed setup before truck runs.

Spreader truck makes three passes over the test area. One to the left, one over the center, and one on the right.

After the truck makes the three passes, the tarp is gathered up and the litter poured into a five gallon bucket.

The amount of litter in the bucket is weighed. The weight is checked on Table 1 to estimate the tons of litter per acre.

Litter in the dish pans is weighed on a portable scale that will measure grams or ounces. Here, Dr. Charles Mitchell is plotting the results on a graph.

Dr. Ted Tyson points out deflector, gate, and spinners.

The position of the deflector has an effect on the spreader pattern. If the pattern is not acceptable, adjustments can be made

If changes are made, tests should be repeated to re-check spreader truck pattern.

Written by Mike Henshaw, County Extension Coordinator
Alabama Cooperative Extension System-Winston County Office
Adapted from Circular ANR-889 by Charles B. Ogburn, Extension Agricultural Engineer (Retired)
Updated on January 20, 2005.

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	Setting flags to mark the location of pans. The flags are set at 0,6,9,12,15, and 18 feet from the trucks path.
	Inexpensive plastic tarp spread on the ground. Tarp has to be weighted or staked down.
	Completed setup before truck runs.
	Spreader truck makes three passes over the test area. One to the left, one over the center, and one on the right.
	After the truck makes the three passes, the tarp is gathered up and the litter poured into a five gallon bucket.
	The amount of litter in the bucket is weighed. The weight is checked on Table 1 to estimate the tons of litter per acre.
	Litter in the dish pans is weighed on a portable scale that will measure grams or ounces. Here, Dr. Charles Mitchell is plotting the results on a graph.
	Dr. Ted Tyson points out deflector, gate, and spinners.
	The position of the deflector has an effect on the spreader pattern. If the pattern is not acceptable, adjustments can be made
	If changes are made, tests should be repeated to re-check spreader truck pattern.