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Dennis Busch, Tim Wagar and Mike Schmitt
Introduction
Laboratory analysis of manure nutrient content is an essential component of crop management planning that can improve farm profitability and the environment. Manure analysis is necessary for application rate planning. Estimates of manure nutrient content are available from a number of published sources, but nutrient composition varies widely between farms due to differences in animal species and management, and manure storage and handling (Table 1). The only method available for determining the actual manure nutrient content for a particular operation is laboratory analysis.
The most important factor in obtaining an accurate sample is proper sampling. Since such a small amount of material is used for analysis, it is essential that the sample submitted represent the manure that is applied to the fields. This fact sheet was developed to answer frequently asked questions related to proper sampling methods, analysis, and interpretation of results.
Table 1
Nutrient analysis of manure collected from 430 farms in Minnesota between 1994 and 1997 |
| |
Liquid
lb./1000 gal. |
Solid
lb./ton |
| |
N |
P2O5 |
K2O |
N |
P2O5 |
K2O |
| Swine |
Farrowing |
27 |
27 |
15 |
-- |
-- |
-- |
| Nursery |
34 |
25 |
18 |
-- |
-- |
-- |
| Gestation |
40 |
42 |
18 |
22 |
27 |
14 |
| Finishing |
53 |
39 |
29 |
22 |
22 |
17 |
| Dairy |
Cows |
25 |
15 |
27 |
11 |
7 |
9 |
| Heifers |
-- |
-- |
-- |
13 |
12 |
19 |
| Beef |
Cows |
-- |
-- |
-- |
15 |
10 |
9 |
| Steers |
-- |
-- |
-- |
14 |
9 |
14 |
| Poultry |
Turkeys |
-- |
-- |
-- |
44 |
63 |
34 |
When is the best time to sample manure - before or during hauling?
These are pros and cons associated with sampling manure prior to hauling and with sampling manure while hauling.
It is recommended that manure be sampled during hauling. The sample will be more accurate and safer. The only drawback to using this method is that the results of this year's sample cannot be used to plan this year's manure applications. However, manure test results can be used to adjust commercial fertilizer application rates and estimate next year's manure nutrient content.
The paragraphs below list some additional factors that should be considered when determining the best time to take manure samples.
Sampling manure before hauling
Pros:
Timeliness - Manure results can be used to determine this year's manure application rates.
Cons:
Accuracy - Retrieving an accurate sampling prior to manure hauling and application may be difficult. Tests may not be as accurate when manure is not thoroughly mixed.
Safety - Sampling manure storage structures can be dangerous. When sampling manure from storage structures, there is always the risk of falling into manure or being overcome by manure gases.
Sampling manure during hauling
Pros:
Accuracy - Tests should be more accurate, because the process of agitating and loading manure helps ensure that samples accurately represent the contents of the storage structure.
Speed - Sampling manure during the application process should require very little time.
Safety - Sampling manure from application equipment is safer because there is less chance of falling into manure or being overcome by gases.
Cons:
Timeliness - The results of the manure sample taken from application equipment during the process of hauling cannot be used to plan this year's manure applications. However, they can be used to determine whether adequate amounts of plant nutrients were applied, and as an estimate for next year's manure nutrient content.
What is the correct sampling procedure?
For best results, sample the manure that is in the tank or spreader box being delivered to the field for application. Such samples will be the most representative because the liquid pit manure is likely to have been agitated in order to load the tank, and semi-solid manure scraped from the barn is moderately mixed after being loaded into a box spreader.
If possible, sample submitted for lab analysis should be a mixture of manure taken from several loads (5-10) representing the beginning, middle, and end of the application process. This will help ensure that manure samples accurately represent the manure being applied.
For liquid manure, retrieve samples with a plastic pail or a coffee can on a pole from the top of the spreader if possible. Otherwise, a sample can be taken from the bottom unloading port. Sampling should be done immediately after filling.
For solid manure, collect manure from application equipment using a pitchfork, shovel, or plastic glove. When sampling solid manure, try to avoid large pieces or chunks of bedding. During the sampling process, place sub-samples in a 5-gallon bucket and store in a cool place.
After collecting 5-10 sub-samples in a 5-gallon bucket, mix sub-samples thoroughly. From this mixture, fill sample jar 3/4 full (allowing room for gas expansion), wipe off sample jar, and seal in a ziplock bag. Manure samples should be frozen prior to mailing in order to slow down any microbial activity, and mailed early in the week so that they will not remain in the post office over the weekend.
Sampling manure from storage structures
An alternative to sampling manure during application is to sample manure from the storage structure prior to application. However, sampling from storage is not as accurate as sampling during application, and it can be more dangerous. For these reasons it is recommended that manure be sampled during application. If time and management practices prevent this, manure can be sampled from the storage structure. Exercise caution!
Liquid manure
A can or other container can be attached to a long pole and dipped into the pit or basin. An alternative method is to use a 1/2" or 3/4", 8-10-ft. PVC pipe. Push the pipe into the manure, avoiding the bottom foot of the structure. Place a hand over the top opening to seal the pipe, pull up, and empty into a bucket.
Solid manure
Stacked, piled, or bedded pack manure can also be sampled in storage, and an average nutrient content estimated. Using a pitch fork or shovel, take 10-20 sub-samples from different depths and locations in the pile or pack. Place the sub-samples in a pile, mix, and obtain a composite sample as described above (again, avoid large pieces of bedding). You may want to take two or more composite samples for analysis, and use the average of the results.
How many samples need to be taken to determine manure nutrient content?
The number of samples that must be submitted in order to be confident of manure nutrient content will vary with manure storage and handling methods. The table below gives guidelines on the number of smaples that should be submitted for different storage structures and explains why additional samples are needed for certain systems.
| Table 2 |
| Storage structure |
Samples needed |
Reason |
| Agitated liquid slurries, under-barn pits, earthen basins, above ground tanks |
1 |
If properly agitated for 2-4 hours prior to sampling, one sample should be sufficient to characterize the manure. One sample should be taken each time the structure is emptied or less often if repeated analysis shows little variation. |
| Liquid slurries |
3 or more |
Several samples are required because solids settle and nutrients tend to stratify in storage. At least three samples are needed and should roughly correspond to the top, middle, and bottom portions of the pit or basin. |
| Lagoon liquids, single or multiple stage solids-separation systems |
1 |
Lagoons that act as settling basins or are used in flush/recycle systems are usually not agitated. Take one sample just from the top 1/2 ft. of liquid at various locations around the lagoon, staying 10-15 ft. away from the edge. Avoid surface scum or debris. |
| Stored solids* (stacking slabs, bedded packs, piles, compost) |
3 or more |
Due to nutrient stratification in storage and the presence of bedding in feed, solid manure is a very mixed material. Fewer samples may be needed for compost that has been mixed by periodic turning and has been covered, or from smaller piles or packs that are spread more frequently. |
| Scrape and haul* |
1 per season |
Samples should be taken at seasonal changes throughout the year to characterize manure. Fewer samples may be needed when animal size, type, numbers, and feeding remain constant. |
| Poultry (in-house systems) |
1 per house |
If manure is sampled prior to loading and application, use a pitchfork to sample to the depth of the floor in 5-10 locations around the house. Sub-samples should be taken from around feeders and waterers in proportion to the areas they occupy. |
| *Where multiple samples are taken, record field locations that correspond to manure samples submitted. |
How often should manure be sampled?
For systems that are emptied or cleaned out once per year, a good rule of thumb is to sample and analyze manure each time it is applied. This is especially true for uncovered lagoons, pits, basins, and stacking slabs. Variations in temperature and precipitation between years will affect changes in nutrient content due to dilution, evaporation, leaching, and volatilization. Manure from under-barn concrete pits or covered above ground tanks will not vary as much between applications, unless the type of animal or other factor changes (species, size, feed, bedding, confinement). Systems emptied twice per year or more may differ between application times, so a fall analysis may not be accurate for planning spring applications.
Keep track of the manure analyses from a particular storage system over a period of time. This will help you determine both the necessary frequency of sampling and an average nutrient content to use for manure application planning. Remember that manure should always be resampled if you change any component of your animal management or manure storage or handling system.
Summary
Laboratory analysis of manure is an important management tool to use crop nutrients profitably and efficiently on the farm. Published estimates of average manure nutrients can be misleading for planning appropriate application rates. The nutrient content of manure can vary from farm to farm and species to species. Therefore, the only reliable method to determine the nutrient levels in manure is to take a representative sample for laboratory analysis.
Depending on the manure handling system, one to several samples may be needed during application or taken at seasonal changes during the year. Multiple samples will cost more (about $20 each), but having more than one test result will mean a much higher level of accuracy for planning manure applications.
A list of manure testing laboratories is available from your county Extension or Soil and Water Conservation District office. Contact the lab for special instructions, sample containers, and mailing boxes. After samples are collected, freeze overnight to halt microbial action and resulting changes in nutrient composition. Fill out the information sheet as completely as possible and enclose with the samples and appropriate fees in the box provided. Packing material placed around the samples will keep them cool until delivery. Mail manure samples early in the week, avoiding weekends and holidays.
The analyses needed for developing a manure application plan are total nitrogen (N, sometimes called total Kjeldahl nitrogen or TKN), phosphate (P2O5), and potash (K2O). Analysis of dry matter, or solids content, is needed if results are reported on a dry matter basis and must be converted to an as-is or wet basis. Most laboratories report results on an as-is basis.
Almost all manure testing labs offer a package of analyses for a set fee. These usually include total N, P2O5, K2O, and solids, and sometimes include ammonium-N (NH4-N). Knowing NH4-N can be useful if this N fraction makes up a large percentage of the total N in the manure. All of the ammonium-N is usually available the first year of application. If this fraction is high (70% or more of total N), then total manure N availability the first year may be somewhat higher than average for a particular manure type.
It is usually not necessary to analyze manure for other mineral constituents such as calcium (Ca), magnesium (Mg), zinc (Zn), sulfur (S), or boron (B). Most manure contains significant quantities of these minerals, and fields with manure histories are rarely deficient. Deficiencies are better managed using soil testing and plant analysis.
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