Odor and Nutrient Management Newsletter

Spring 1999

Tips for spreader calibration

by Gina Hanson, Manure Management Specialist, Northeast Iowa Demonstration Project

Manure spreader calibration is key to determining accurate manure nutrient contributions. For the past six years the Northeast Iowa Demonstration Project (NEIDP) at Postville, Iowa has helped local farmers determine manure application rates through spreader calibration.

Calibration Method 1

Start by determining how much manure is on each load. This can be measured in tons or gallons. The most accurate measurement is to weigh the spreader both full and empty. You may use portable scales or weigh a load of manure at your local coop. In addition, your local extension office or Natural Resources Conservation Service (NRCS) office may know where to locate a set of portable scales.

Table 1. Manure spreader calibrations for Northeast Iowa (hydraulic endgate).
Spreader size (bushels) Tons of manure per load *
90 1.45
110 1.75
150 2.15
180 2.50
220 3.0
260 3.50
290 4.0
320 4.30
390 5.40

Table 1. shows results from more than 100 endgate spreaders calibrated in northeast Iowa. There is no significant difference in the total weight of more liquid manure from the feeding floor and manure with bedding in the same size manure spreader. There is a difference in weight per cubic foot, however bedded manure usually is heaped higher on the spreader and the extra volume makes up for the weight deficiency.

*It is best to weigh a load and compare the results to the table values

Photo spreaderYou also can estimate the amount of manure on a load based on spreader size. For liquid manure, use 90 % of tank capacity to account for foaming and other factors. A 3,000 gallon tank spreader should hold 2,700 gallons of liquid manure.

For conventional solid manure spreaders, consult your spreader's user's manual for the capacity in cubic feet, bushels, or gallons. Use the following conversions to determine manure spreader capacity:

1 gallon of liquid manure weighs 8.34 pounds
1 bushel of manure weighs 77.4 pounds
1 cubic foot of manure weighs 62.4 pounds
7.48 gallons per 1 cubic foot of manure
1.24 cubic feet per bushel of manure
0.81 bushel per 1 cubic foot of manure

If the user’s manual is not available, measure the bed. Multiply the length by the width by the height of a level full spreader to determine the volume in cubic feet. Then multiply the result by 62.4 pounds per cubic foot to calculate the weight. Divide the result by 2,000 pounds/ton to determine the tons per load.

In some instances it is best not to fill the spreader to capacity, to prevent spills on the way to field. When using book values, multiply by 80 to 90 percent of capacity to account for this difference. Spreaders weighed with portable scales in Northeast Iowa averaged 80 percent of the stated bushel capacity.

Once you know the amount of manure per load, the next step is to spread the load, measuring the distance traveled. Also measure the spreader application width, keeping spread patterns in mind. Multiply the distance traveled to spread the load by the width the spreader is covering with manure. Divide that number by 43,560 (the area in square feet in one acre) to determine acres spread with manure.

You now have the area in acres covered with one load of manure. Divide the number of gallons or tons of manure applied in one load by the number of acres covered. The result is in gallons or tons per acre.

Calibration Method 2

Count the number of loads applied to a field and divide the result by the number of acres in the field. Multiply this by the tons or gallons per load to determine the application rate per acre.

Finally, take a good look at the uniformity of spread patterns in the field. When making a pass through the field, a small amount of overlap is required for uniform manure distribution. However, if there is too much or too little overlap, application rates will be uneven and it will be hard to use manure as a credible nutrient resource.

For more information, contact Gina Hanson, Northeast Iowa Demonstration Project, Postville, IA, (319) 864-3999.

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