Title

Manure Spreader Calibration For Nutrient Management Planning

(NM1418, Revised June 2026)
File
Publication File:
Summary

Livestock manures contain many beneficial and valuable plant nutrients. However, if the manure application equipment is not properly calibrated, these valuable nutrients may be wasted by overapplication or crop yield goals may not be met due to underapplication. This publication explains two simple manure spreader calibration techniques.

Lead Author
Lead Author:
Revised by Mary A. Keena, Livestock Environmental Management Specialist
Availability
Availability:
Web only
Publication Sections

Table of Contents

Purpose for Calibration

Livestock manures contain many beneficial and valuable plant nutrients, mainly nitrogen (N), phosphorus (P), potassium (K), sulfur (S) and micronutrients. However, if the manure application equipment is not properly calibrated, these valuable nutrients may be wasted by overapplication or crop yield goals may not be met due to underapplication.

Misapplication of manure also increases the risk of environmental pollution. Environmental issues with manure pollution pertain mainly to bacterial pathogens, P in runoff entering surface waters and N leaching through the soil to groundwater. These factors can cause health and environmental issues (Freitas and Burr, 1996).

Nutrient Properties

Manure has many inorganic (mineralized) and many organic (immobilized) nutrients. The immobilized nutrients are not plant available until microbes break down the manure, releasing the nutrients into the soil (mineralization).

Roughly 50% of the N, 80% of the P and 90% of the K found in manure is plant available during the first growing season after manure application. Most of the remaining immobilized nutrients will be mineralized during the following growing season.

The added organic matter from manure promotes sustained fertility due to a slow release of nutrients and increase in soil cation exchange capacity (CEC), which is the soil’s capacity to hold onto positively charged ions.

Soil characteristics such as water-holding capacity, water infiltration, bulk density and soil buffering can be improved by using manure with a properly planned and practiced nutrient management plan. Economic benefits arise from increased soil health, crop production and money saved from reduced fertilizer costs.

Testing Manure

Manure composition can vary greatly due to differences such as animal species, bedding, diet, climate and storage facilities. Average values (Table 1) can help develop a nutrient management plan, but experts highly recommend having a manure sample analyzed by a specialized lab before application to better manage nutrients from manure, ensuring safe environmental practices and meeting crop yield goals.

Refer to NDSU Extension publication “Manure Sampling for Nutrient Management Planning” (NM1259) for sampling methods and analysis interpretation

Table 1. Manure book values for various livestock species and categories.
AnimalNP2O5K2O
------------------ Pounds Per Ton ------------------
Beef

13

6

12

Sheep

20

10

20

Poultry
Layer

34

51

26

Tom turkey

40

50

30

Equine, sedentary

7

2

2

----------- Pounds Per 1,000 Gallons -----------
Dairy, lactating

54

28

30

Swine
Gestating

55

36

45

Finishing

93

37

47

Sources:
Midwest Plan Service, 2004
Keena and Augstin, 2026

Calibration Methods

Sheet Method

This method works well for solid manure applications.

Materials:

  • Tarps/sheets (at least three) of known area (length [feet] x width [feet] = area [feet2]). Landscaping fabric works well because applied manure will not slide off as easily as it will on a plastic sheet.
  • 5-gallon bucket
  • Scale

Procedure:

  • Weigh the bucket and a sheet to tare the weight off the manure.

  • Lay out the sheets in a row and anchor them with a few rocks or stakes. Photo 1.

    Figure 1
  • Start the tractor and turn the spreader on. Allow time for the spreader to start spreading. Photo 2.

  • Record your tractor gear, engine’s revolutions per minute (rpm) and spreader settings.

    Figure 2

  • Drive over the sheets, applying manure over them. Photo 3.

    Figure 3

  • Retrieve the manure-covered sheets and weigh them in the bucket. Photos 4 and 5.

    Figure 4
    Figure 5
  • If a sheet measuring 21.8 feet2 (3 feet by 7 feet 4 inches or 4 feet by 5 feet 6 inches) is used, then the weight in pounds of manure on the sheet is equal to tons/acre (Table 2, Example 1). Example 2 shows how to determine the application when a different size sheet is used (see Table 3 for some examples of tarp sizes, manure weight and corresponding application rate).

  • The application rate is given by the following expression: Rate (tons/acre) = (pounds of manure on sheet x 21.8) ÷ sheet area (feet2).

    Table 2. Sheet Method Worksheet
    Manure on Sheet (lbs)MultiplyCorrection Factor (21.8)DivideSquare Feet of Sheet
    (length x width)    		EqualsTons of Manure Per Acre
    Example 1

    21.25

    x

    21.8

    /

    21.8

    =

    21.25

    Example 2

    21.25

    x

    21.8

    /

    24

    =

    19.3

    Sheet 1

    x

    /

    =

    Sheet 2

    x

    /

    =

    Sheet 3

    x

    /

    =

    This procedure also should be replicated three or more times and averaged to help account for variability (Jokela, 2008).
    Table 3. Tarp sizes, manure weight and corresponding manure application rate.
    Manure
    Weight    		Tarp Size, feet

    5x7

    6x8

    6x4, 8x3a

    4x10, 8x5b

    lbs.

    Manure Application Ratec, ton/acre

    2

    1.2

    0.9

    1.8

    1.1

    4

    2.5

    1.8

    3.6

    2.2

    6

    3.7

    2.7

    5.4

    3.3

    8

    5

    3.6

    7.3

    4.4

    10

    6.2

    4.5

    9.1

    5.4

    12

    7.5

    5.4

    10.9

    6.5

    14

    8.7

    6.4

    12.7

    7.6

    16

    10

    7.3

    14.5

    8.7

    18

    11.2

    8.2

    16.3

    9.8

    20

    12.4

    9.1

    18.2

    10.9

    22

    13.7

    10

    20

    12

    24

    14.9

    10.9

    21.8

    13.1

    26

    16.2

    11.8

    23.6

    14.2

    28

    17.4

    12.7

    25.4

    15.2

    30

    18.7

    13.6

    27.2

    16.3

    32

    19.9

    14.5

    29

    17.4

    34

    21.2

    15.4

    30.9

    18.5

    36

    22.4

    16.3

    32.7

    19.6

    38

    23.6

    17.2

    34.5

    20.7

    40

    24.9

    18.2

    36.3

    21.8

    42

    26.1

    19.1

    38.1

    22.9

    44

    27.4

    20.0

    39.9

    24.0

    46

    28.6

    20.9

    41.7

    25.0

    48

    29.9

    21.8

    43.6

    26.1

    50

    31.1

    22.7

    45.4

    27.2

    a Halves of a 6- by 8-foot tarp.
    b Halves of a 10- by 8-foot tarp.
    c Manure Application Rate = (Manure Weight [lbs.] x 21.8)

What is the magic 21.8 number?

To convert the weight of manure applied to the area of the calibration strip or tarp (pounds/square feet) to tons/acre, we need to multiply the weight in pounds by 43,560 square feet (= 1 acre) and divide it by 2,000 pounds (= 1 ton).

Instead of doing a two-step calculation, we calculate a factor that will convert at the same time the weight from pounds to tons and the area from square feet to acre.

The factor 21.8 is the rounded value for the division of 43,560 square feet/acre by 2,000 pounds/ton (= 21.78).

Axle Weight Method

This method works for solid and liquid manure applications.

Materials:

  • 100-foot measuring tape or a measuring wheel.
  • Scale capable of weighing the manure spreader (truck scales or portable axle scales work well).

Procedure:

  • Weigh the manure spreader loaded. In the event the spreader is a tandem axle and the scale is unable to weigh both axles at the same time, each axle may be weighed individually and their weights can be added. (If using a tractor-pulled spreader and parking the tractor and spreader on the scale is not possible, be sure to lower the manure spreader jack onto the scale to take weight off the tractor tongue.).
  • Record tractor gear, engine RPM and spreader settings.
  • Apply manure to a desired area or measure the area after manure application (length [feet] x width [feet] = area [feet2]).
  • Weigh the spreader after application.

The application rate can be calculated by the following expression:

Rate (tons /acre) = (loaded spreader weight [pounds] – empty spreader weight [pounds]) x 21.8 ÷ application area [feet2] (Table 4).

Table 4. Axle Weight Method Worksheet
Loaded
Spreader
Weight
(lbs.)		MinusSpreader
Weight After
Application
(lbs.)		EqualsManure
Weight
(lbs.)		TimesCorrection
Times		DivideApplication
Area (feet2)		EqualsManure
Application
Rate
(tons/acre)
Example 1

37,188

-

19,321

=

17,867

x

21.8

/

16,438

=

23.7

Application 1

-

=

x

21.8

/

=

Application 2

-

=

x

21.8

/

=

Application 3

-

=

x

21.8

/

=

Application 4

-

=

x

21.8

/

=

This procedure might be the most time consuming, but it is the most accurate because it can account for variability within the application procedure.

These techniques sufficiently meet calibration criteria stated in the USDA-NRCS North Dakota 590 Nutrient Management Standard.

References

Freitas, R.J., and M.D. Burr. 1996. Animal Wastes. In Pollution Science. I.L. Pepper, C.P Gerba and M.L. Brusseau (ed). Academic Press. San Diego, Calif.

Jokela, B. Verified April 21, 2021. Manure Spreader Calibration. The University of Vermont Extension. www.uvm.edu/sites/default/files/Agriculture/CVCROPS/ManureCalibration.pdf

Keena, M.A. 2026. Nutrient Characteristics of Solid Beef Manure in North Dakota. www.ag.ndsu.edu/publications/livestock/nutrient-characteristics-of-solid-beef-manure-in-north-dakota

Midwest Plan Service. 2004. Manure Characteristics Manure Management Systems Series. Section 1, Second edition.

Refer to NDSU Extension publication “Manure Sampling for Nutrient Management Planning” (NM1259) for sampling methods and analysis interpretation.

This publication was authored by Chris Augustin, NDSU Dickinson Research Extension Center director; Ron Wiederholt, former Extension nutrient management specialist; and Teresa Dvorak, former Extension livestock nutrient management specialist, NDSU, 2009, and revised by Paulo Flores, NDSU assistant professor, 2015.

Photos taken at the Carrington Research Extension Center by Mary Keena.