G1335 • Index: Soil Management

Fertility • 2006, Revised December 2015

Determining Crop Available Nutrients from Manure

Charles A. Shapiro, Soil Scientist, Crop Nutrition

Leslie Johnson, Animal Manure Management Project Coordinator

Amy Millmier Schmidt, Livestock Bioenvironmental Engineer

Richard K. Koelsch, Extension Specialist

This NebGuide discusses the availability and use of manure nutrients for field crop production.

When managed correctly, nutrients in livestock manure can be a valuable resource. When managed improperly, however, these same nutrients represent a potential environmental pollutant. Accurate crediting of manure nutrients within a total crop nutrient program is fundamental to utilizing manure as a resource. This NebGuide illustrates how to estimate the crop available manure nutrients (part c, Figure 1) and calculate an agronomically based manure application rate. There are other tools available that do the calculations for you. This NebGuide will explain each step of the process. After understanding how and why these calculations are made, the tools offer fast and accurate ways to work with multiple fields and manure sources. To illustrate the calculations, an example calculation is provided and a worksheet is included, allowing you to determine manure availability for your situation.

To accurately credit crop available manure nutrients, three pieces of information are needed:

  1. 1. Manure nutrient of concentration at time of land application—the concentration of individual nutrients in manure measured as pounds of nutrient per unit of manure (ton, 1,000 gallons, or acre-inch).
  2. 2. Manure application rate—the rate at which manure is applied to the land measured as tons, 1,000 gallons, or acre-inches.
  3. 3. Manure nutrient availability factors—the percentage of nutrients in manure available to the crop in a given year.

Figure 1. Three key estimates needed to use manure nutrients as a resource.

Estimating Manure Nutrient Concentration

Knowing the concentration of nutrients in manure is as crucial as knowing those facts about commercial fertilizer. Table 1 provides estimates of typical manure nutrient concentrations. Because manure nutrient content can vary with livestock species, manure moisture, livestock diet, and collection and storage losses, a manure analysis is preferable to using table values for an accurate estimate. Where manure is stored outdoors, sampling on a seasonal basis (when significant quantities of manure are land applied) is recommended.

Table 1. Typical nutrient content of manure. Because of variability between farms, individual manure analysis is preferable to the estimates below.

% Dry Matter Nitrogen
Ammonium-N Organic-N P2O5 K2O
Slurry Manure (lb of nutrient per 1,000 gallons of manure)

Dairy

8

12

13

25

40

Beef

10

21

24

24

36

Swine (finisher, wet-dry feeder)

9

42

17

40

24

Swine (slurry storage, dry feeder)

6

28

11

34

24

Swine (flush building)

2

12

5

13

17

Layer¥

42

20

59

37

Dairy (lagoon sludge)*

10

4

17

20

16

Swine (lagoon sludge)

10

6

16

48

7

Solid Manure (lb of nutrient per ton of manure)

Beef (dirt lot)

67

2

22

23

30

Beef (paved lot)*

29

5

9

9

13

Beef (bedded pack barn)

30

1

17

11

14

Swine (hoop barns)

40

6

20

15

18

Dairy (scraped earthen lots)

46

14

11

16

Broiler (litter from house)

69

15

60

27

33

Layer

41

18

19

55

32

Turkey (grower house litter)

70

44

15

30

Liquid Effluent from lagoon or holding pond (lb of nutrient per acre-inch)

Beef (runoff holding pond)

5

44

5

20

109

Swine (lagoon)

0.40

91

45

104

192

Dairy (lagoon)

2

181

83

302

Values are based upon ASABE, 2005, D384.2; Manure Production and Characteristics with exception of those noted with the superscripts described below. Please note that these values have not been updated by the ASABE since 2005 and, therefore, might not accurately reflect manure produced by livestock systems that are feeding distillers grains.

Values based upon Iowa State publication PM1867, revised 2015.

Empty spaces indicate we do not have reliable numbers for this specific manure compound.

¥ Values based upon North Carolina State University publication AG-439–5, revised 1997.

Values based upon University of Missouri publication EQ 352, revised 2003.

A manure analysis should include:

Additional information on manure sampling is available in Manure Testing for Nutrient Content (NebGuide G1450).

Estimating Manure Application Rate

If manure nutrients are to be managed as a nutrient resource, the application equipment must be managed as a fertilizer applicator. Knowledge of manure application rate, like knowledge of fertilizer application rate, is key to managing nutrients applied to crops. Manure application rate can be estimated by one of the following:

  1. 1. Using one of the calibration methods detailed at go.unl.edu/calibration.
  2. 2. Maintaining a record of total manure applied to a field (i.e., total number of loads × average capacity ÷ the field’s area). The Nutrient Management Record Keeping Calendar is a helpful tool for record keeping. More information about the calendar can be found at: go.unl.edu/ec136.

Estimating Crop Available Nutrients

Manure application rate and a manure analysis provide the information needed to estimate total manure nutrients applied. The “total manure nutrients,” however, is less important than “crop available nutrients.” The process for estimating crop available nutrients is illustrated in Figure 2. A worksheet for completing the calculations (Table 2) will assist in making this estimate.

{Note: See PDF for Table 2.}

Some manure nutrients become available slowly through mineralization in the soil. Mineralization is a process by which soil microorganisms decompose organic nutrients into a mineral inorganic, or plant available form. An estimate of crop available phosphorus and potassium is reasonably simple. Seventy percent of the phosphorus and 70 to 90 percent of the potassium is available to the crop during the year it is applied. Many production fields in Nebraska are not deficient in these two nutrients, so the manure application is more of a maintenance application. When the soil does not test low, all phosphorus and potassium can be credited since the rest becomes available in the subsequent years.

Determining nitrogen availability, however, is more complex. The availability of ammonium and organic-nitrogen for specific livestock species, application methods, and other factors can be found in Figure 2. Ammonium and organic-nitrogen originate from the urine and feces, respectively. The ammonium fraction’s availability to the crop (Box I, Figure 2) depends upon both the time between manure application and incorporation into the soil and the environmental conditions. If manure is surface applied, ammonium (NH4) is converted over several days to ammonia (NH3) and lost by volatilization. Warmer temperatures accelerate this loss. If manure is mixed into the soil, the ammonium either is directly available to the plants or converts to another plant available form, nitrate-nitrogen (NO3).

Organic-nitrogen is mineralized to ammonium over several years at a rate affected by soil temperature, soil water content, the characteristics of the manure, and other factors. During the cropping season following application, between 25 and 50 percent of the organic-nitrogen is typically available (Box II, Figure 2). Over the next several years, additional organic-nitrogen is mineralized to crop available forms in decreasing amounts (bottom right of box II, Figure 2). For example, as a general rule, mineralization of stored swine manure will be approximately 35 percent, 15 percent, 7 percent, and 4 percent of the organic-nitrogen during the year manure is applied, one year later, two years later, and three years later, respectively.

Calculating Crop Available Nutrients

At this point, information should have been collected for 1) nutrient concentration of the manure, 2) manure application rate for the current year and the past three years, and 3) availability of organic-nitrogen, ammonium-nitrogen, phosphorus, and potassium. Table 2 can now be used to complete a calculation for crop available nutrients. For determining crop available nitrogen in Table 2, follow these steps:

  1. 1. Select the units used to measure manure application rate. Replace all “?” within the calculations with either tons, 1,000 gallons, or acre-inches of manure or effluent.
  2. 2. Enter the manure application rate and nutrient concentration and calculate total nitrogen application.
  3. 3. Enter the total nitrogen application and manure nutrient fraction available, and calculate the available nitrogen for ammonium, organic-N, and organic-N from past applications separately.
  4. 4. Sum the estimated available nitrogen from ammonium, organic-N, and organic-N from past applications.

An example is presented in Table 2 for cattle feedlot manure applied at a rate of 28 ton/ac this year and two years ago. Manure is disked into the soil within 24 hours. The producer’s manure analysis indicates nutrient concentrations of 5 lb of NH4/ton, 13 lb of organic-N/ton, 12 lb of P2O5/ton, and 21 lb of K2O/ton. When manure was applied 2 years ago, there was 11 lb of organic-N/ton.

A much simpler estimate of crop available phosphorus and potassium can also be completed in Step 5. The results of these calculations can be summarized in Step 6.

Figure 2. Availability factors for manure nitrogen.

Soil Testing and Crop Monitoring

The previous procedures have provided a “calculated” estimate of nutrient availability from manure. Soil testing provides a “field measurement” of residual nutrients. For a producer who regularly soil tests, is this calculated nitrogen availability in subsequent years estimate necessary? Yes, it is. The reasoning follows:

A deep soil test measures soil nitrate-N at the time of sampling. The above calculations estimate organic and ammonium nitrogen accessible to the crop during the growing season and in future years. Although most manure nitrogen will eventually be converted to nitrate nitrogen, this has not happened at the time soil samples are typically taken (fall, winter, or early spring). A soil test for nitrate nitrogen will not account for the future nitrogen available from manure. Thus, the “field measured” and “calculated” values are independent sources of nitrogen and should be added together. In the future we might have soil tests that accurately predict “mineralizable nitrogen,” but to date these have not been proven to be accurate under all field conditions.

The amount of nitrogen provided by the manure nitrogen credit is an estimate based on average conditions. An alternative strategy is the presidedress nitrate test (PSNT), which may provide a more accurate prediction of when manure released nitrogen is sufficient to produce maximum yields in corn. The PSNT test is a one-foot soil sample taken in early June or at the six to eight leaf stage. The soil is analyzed for nitrates. By this time of the growing season, manure nitrogen is mineralizing to nitrate, and this test will help determine if there is enough nitrogen available. In Iowa and other states a soil nitrate level of over 25 ppm is usually sufficient for maximum corn production. Nebraska has not published recommendations for this test, but refers people to the Iowa publications.

Corn can be monitored to determine if a nitrogen deficiency is developing by use of a chlorophyll meter or other canopy sensor. Several sensors are available commercially. What is still unknown is whether their calibrations are adequate for manured fields since there might be more future N available than under non-manured fields. Under irrigated conditions, producers have the option of applying additional nitrogen when needed through fertigation. Under rainfed conditions, additional N is difficult to apply after the 11-leaf stage unless high clearance ground application is used.

Phosphorus and potassium application needs can be determined by soil testing. Regular soil testing of fields receiving manure will document phosphorus and potassium status.

Using any one of these techniques or a combination will allow more accurate crediting of manure nutrients with confidence. The “calculated” estimate of manure nitrogen will remain an important pre-growing season planning tool for manure nutrient sources.

Additional Resources

All University of Nebraska—Lincoln resources for manure nutrient management planning can be found online at manure.unl.edu and soil testing and nutrient recommendations can be found at cropwatch.unl.edu/soils. The manure website contains software tools, sample records, regulatory information, and other tools associated with nutrient management planning.


This publication has been peer-reviewed.

UNL Extension publications are available online at http://extension.unl.edu/publications.

Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska—Lincoln cooperating with the Counties and the United States Department of Agriculture.

University of Nebraska—Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska—Lincoln and the United States Department of Agriculture.

© 2006–2016, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska—Lincoln Extension. All rights reserved.

Once the available nutrients are determined, the next step is to fit this information into a nutrient management plan. Extension Circular EC117, Fertilizer Suggestions for Corn, details how to determine the total nutrient needs based on soil tests and yield expectation. The Nutrient Management for Agronomic Crops in Nebraska, EC155 (revised 2014) provides nutrient recommendations for many Nebraska crops. Calculating the Value of Manure for Crop Production, G1519 assists in calculating the fertilizer value of the nutrients to be applied to a particular field.