G1335
This NebGuide discusses the availability and use of manure nutrients for field crop production.
Rick Koelsch, Livestock Environmental Engineer
Charles Shapiro, Soil Scientist, Crop Nutrition
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. To illustrate this process, example calculations are provided and a worksheet is included allowing you to complete the calculations as well.
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| Figure 1. Three key estimates needed to use manure nutrients as a resource. |
To accurately credit crop available manure nutrients, a producer needs three pieces of information:
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. Manure application rate — the rate at which manure is applied to the land measured as tons, 1,000 gallons or acre-inches.
3. Manure nutrient availability factors — the percentage of nutrients in manure available to the crop in a given year.
Estimating Manure Nutrient Concentration
Knowing the concentration of nutrients in manure is as crucial as knowing those facts about commercial fertilizer. Table I 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 I. Typical nutrient content of manure. Because of variability between farms, individual manure analysis is preferable to the estimates below. |
| |
|
Nitrogen
|
|
|
Ammonium-N
|
Organic-N
|
P2O5
|
K2O
|
| Slurry Manure |
|
———— (lbs. of nutrient per 1,000 gallons of manure) ————
|
Dairy
Beef
Swine (finisher, wet-dry feeder)
Swine (slurry storage, dry feeder)
Swine (flish building)
Layer
Dairy (lagoon sludge)*
Swine (lagoon sludge) |
8
29
9
6
2
11
10
10
|
12
5
42
28
12
37
4
6
|
13
9
17
11
5
20
17
16
|
25
9
40
34
13
51
20
48
|
40
13
24
24
17
33
16
7
|
| Solid Manure |
|
—————— (lbs. of nutrient per ton of manure) —————
|
Beef (dirt lot)
Beef (paved lot)*
Swine (hoop barns)
Dairy (scraped earthen lots)
Broiler (litter from house)
Layer
Turkey (grower house litter) |
67
29
57
46
70
40
70
|
2
5
4
3
15
18
|
>22
9
13
14
60
19
|
23
9
20
11
27
55
15
|
30
13
16
33
31
30
|
| Liquid Effluent from lagoon or holding pond |
|
————— (lbs. of nutrient per acre-inch) —————
|
Beef (runoff holding pond)
Swine (lagoon)
Dairy (lagoon) |
0.25
0.40
2
|
71
91
317
|
8
45
362
|
47
104
674
|
92
189
1082
|
| Value based upon ASAE, 2005, D384.2; Manure Production and Characteristics with exception of those “*”. |
A manure analysis should include:
- Both ammonium-nitrogen and organic-nitrogen (or total nitrogen). Knowing two of the three values means you can calculate the third.
Total-N = Ammonium-N + Organic-N
Nitrogen is excreted in two forms (Figure 2). About one-half of the excreted nitrogen is a stable organic-nitrogen present in the feces. The other half is excreted as urea in urine, which decomposes rapidly to ammonium-N (NH4+).
- Phosphorus and potassium as P2O5 and K2O equivalents.
- Nutrients in the same units of measure as you calibrate your manure application system. If manure application is measured by tons per acre, request the analysis be reported as pounds of nutrient per ton.
- Nutrients on a “wet” or “as is” basis since you are calibrating application equipment on a wet manure basis.
Additional information on manure sampling is available from Sampling Manures for Nutrient Analysis (NebGuide G1450) and Manure Testing: What to Request? (NebFact NF507).
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:
- Using one of the calibration methods detailed in Nebraska CNMP Application Workbook (EC720), pp. 87-88, available online at http://cnmp.unl.edu/landapplicationworkbook.html.
- Maintaining a record of total manure applied to a field (i.e. total number of loads x average capacity ÷ the field’s area).
Estimating Crop Available Nutrients
Manure application rate and a manure analysis provides 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 II) will assist in makng this estimate.
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.
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 (left-hand box, 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 moisture, the characteristics of the manure and other factors. During the cropping season following application, between 25 and 50 percent of the organic-nitrogen is available (middle box, Figure 2). Over the next several years, additional organic-nitrogen is mineralized to crop-available forms in decreasing amounts (right hand box, Figure 2). For example, 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.
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1Incorporation can be accomplished by tillage or by a 0.50 inch or greater rainfall.
2Organic-N availability assumes spring seeded crops such as corn and soybeans. For winter or spring manure application prior to planting small grains, multiply organic-N availability factor by 0.7. |
| Figure 2. Availability factors for manure nitrogen. |
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 II can now be used to complete a calculation for crop available nutrients. For determining crop available nitrogen in Table II, follow these steps:
- 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.
- Enter the manure application rate and nutrient concen?tration and calculate total nitrogen application.
- 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.
- Sum the estimated available nitrogen from ammonium, organic-N, and organic-N from past applications.
An example is presented in Table II for cattle feedlot manure applied at a rate of 28 t/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.
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.
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 estimate necessary?
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 through the growing season. 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.
The amount of manure nitrogen credit is an estimate based on average conditions. An alternative strategy is the presidedress nitrate test (PSNT) which may be a more accurate predictor of when manure release is sufficient to produce maximum yields in corn. The PSNT test is a one-foot soil sample taken in early June or at the 6 to 8 leaf stage. The soil is analyzed for nitrates. By this time of the growing season, manure nitrogen is mineralizing to nitrate. In Iowa and other states a soil nitrate level of over 25 ppm is usually sufficient for maximum corn production.
Corn can be monitored to determine if a nitrogen deficiency is developing by use of a chlorophyll meter. Under irrigated conditions additional nitrogen can be applied when needed with the irrigation system. In the near future remote sensing may allow monitoring of nitrogen status without the need to sample individual plants.
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.
Once the available nutrients are determined, the next step is to fit this information into a nutrient management plan. NebGuide G174, Fertilizer Suggestions for Corn, details how to determine the total nutrients needs based on soil tests and yield expectation. The Nebraska CNMP Application Workbook (EC720) provides reference tables for nutrient recommendations for many common crops.
Additional Resources
All University of Nebraska–Lincoln resources for nutrient management planning can be found online at http://cnmp.unl.edu. The Web site contains software tools, sample records, regulatory information, and other tools associated with nutrient management planning. Of particular value are two software tools, UNL’s Manure Use Planner and Purdue’s Manure Management Plan. These tools can be downloaded at no cost from the CNMP Web site.
