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 also 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. The only method available
for determining the actual manure nutrient content for your particular
operation is with laboratory analysis. 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. The following
guidelines outline proper technique for obtaining samples as well as
handling and transport.
When You Should Sample
Liquid manure
samples can either be taken at hauling time, or directly from the waste
lagoon. For safety and best results, it is recommended that manure be
sampled during hauling. The sample will be more accurate because it has
been mixed and safer to obtain. 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. This is because samples are taken during
application periods and lab results can take up to a week to be
returned. Additionally, manure results will vary throughout the year as
dilution or nutrient influx occurs. However, manure test results can be
used to adjust application rates made later in the year and estimate
next year's manure nutrient content, if all variables (i.e., cow
numbers, rainfall, inflow sources, etc.) stay relatively the same.
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 factors change
(i.e., 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.
Sampling from Tanker Truck
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 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.
Ideally, the 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. After collecting 5-10 sub-samples in a
5-gallon bucket, mix sub-samples thoroughly. From this mixture, fill a
clean/sterile sample jar 3/4 full (allowing room for gas expansion),
wipe off sample jar, and seal in a bag. Be sure to write the date,
sample number, and any other pertinent information on the jar. Manure
samples should be stored in a cool, dark place and sent to the
laboratory within 12-24 hours of collection. If this is not possible,
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 from a Storage Lagoon
An alternative to sampling manure during application is to sample
manure from the storage structure prior to application. However,
sampling from storage lagoons 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.
Lagoon samples should be taken with a plastic pail or a coffee can on
a pole from varying locations and depths of the lagoon. If a can or
other container cannot 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. Do not collect samples from areas that have
uncharacteristic crusts or floating chunks on the surface. Collect
anywhere from 10-20 sub-samples in a 5-gallon bucket, mix sub-samples
thoroughly. From this mixture, fill a clean/sterile sample jar 3/4 full
(allowing room for gas expansion), wipe off sample jar, and seal in a
bag. Be sure to write the date, sample number, and any other pertinent
information on the jar. Manure samples should be stored in a cool, dark
place and sent to the laboratory within 12-24 hours of collection. If
this is not possible, 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.
Solid Manure Sampling
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 place a composite sub-sample
of the pile (avoid large pieces of bedding) into a large airtight bag.
You may want to take two or more composite samples for analysis, and use
the average of the results. Write the sample number, date, and other
pertinent information on the bag.
Keep track of all 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.