A recent
survey of manure handling practices used by Ohio dairies, indicates that about
50% have the potential to use composting to move nutrients off-farm economically
and create a value-added product. The
feasibility of composting manure varies depending on the manure, bedding and
amendments, which may be needed to reduce moisture in dairy or swine manure.
Research at the OARDC evaluated windrow composting of three mixtures:
dairy manure amended with sawdust, dairy manure amended with straw; and
swine manure from a High Rise Hog facility which used wood shavings as bedding.
In addition, the effectiveness of composting sand-bedded dairy manure was
evaluated. These studies yielded
the following results:
Discussion:
Harry
Hoitink (OSU) asked if the lower somatic cell count (SCC) for dairy cows bedded
on sand is reflected in lower infection rates.
Michel noted that producers receive a premium for milk with levels below
a specified SCC. SCC’s can be
reduced for organic bedding if it is well managed.
Jeff LeJeune (OSU) commented that clinical mastitis is not necessarily
based on SCC. (For a brief review
of SCC and mastitis, see summary of Dr. Larry Smith’s seminar at http://www.oardc.ohio-state.edu/ocamm/smith.htm)
Ted Short (OSU)
commented that it is generally assumed that composting results in a significant
loss of nitrogen. Why was that not
the case in these studies? Michel
noted that the compost had higher than average C:N ratios as a result of the
carbon-based amendments that were added to the manure to reduce the moisture
content.
Lynn Willett
(OSU) asked when the initial nitrogen measurement was made. Michel responded that the initial measurement was made after
the manure was mixed with the amendment. Willett
suggested that additional nitrogen would have been lost during transport of the
manure from the barn to the compost pad. Michel
agreed but observed that such a loss would be true whether the manure was
transported to a field for application or for any other manure management
strategy.
John Smith (OSU)
asked what C:N ratio is recommended to minimize nitrogen loss. Michel suggested a ratio of 30:1. Harry Hoitink (OSU) commented that differences in the
decomposition of different amendments needs to be considered in addition to the
carbon content.
Smith,
referring to data that indicated straw amended dairy manure did not heat as
effectively, asked if the chopping the straw would have an impact.
Michel noted that chopped straw had not been tried as an amendment but
suggested that it should increase the composting rate.
A Columbus
participant asked if the facility where sand (from a sand-bedded dairy) is added
to composted yard trimmings had tested for pathogen reduction and, if so, at
what point in the process. Michel
responded that pathogen testing in this system needs to be evaluated.
Currently, the materials are mixed with 1 part sand to 2 parts yard
trimming compost, on a volume basis.
Srinand
Sreevatsan (OSU) questioned the effect of composting on spore counts such as
bacilli. Michel
noted that, to date, this has not been evaluated, but needs to be.
Hoitink added that the literature indicates that for some heat resistant
microbes, anaerobic decomposition followed by aerobic composting can be
effective for destroying heat resistant microbes.
Hoitink
asked what composting system is most practical for a livestock operation.
Michel noted that an important consideration is minimizing the amount of
material, especially amendments, but there are trade offs.
While straw has a higher volume initially than sawdust, chopping it first
should help. While
sawdust has a lower volume and heats well in the early stages, it can require
more time (200 days to 1 year) to reach stability.
Hoitink
questioned the feasibility of static piles versus windrows.
Michel responded that in the study, the windrow size was probably too
small. Optimizing pile size is
important in managing moisture efficiently.
Hoitink suggested that a static, aerated pile under a pole barn would
require a smaller area than windrows and that the cover could help with moisture
issues. Michel noted that static
piles might become anaerobic in the center if too large.
A fleece blanket (designed to permit transfer of air but not moisture)
covering windrows may be a cheaper alternative to a pole barn.
Additional research is needed to evaluate optimal size.
Willett
questioned whether temperature differentials within the compost pile result in
some materials not reaching the temperatures (55 degrees C for 3 days) needed
for pathogen control. Michel noted
that the temperatures reported were based on an average from six locations
within the windrow taken over a period of 10 days.
During that time, the windrow was turned 2 to 3 times to mix the
material. This method should result
in all material reaching the required temperature. The exception could be the straw amended manure as high
temperatures were not consistent during the first 10 days.
Michel also
noted that during composting, the substrate changes resulting in a change in the
microbial community present. Research
on composted yard trimmings (which usually only reach a maximum of 50-55 degrees
C) demonstrated that the microbial population does change over time.
After 8 days, there was a significant change in the microbes of the genus
containing E. coli and Salmonella. However,
since some pathogens can cause disease at very low levels, additional research
is needed.
Notes
by Mary Wicks
The OCAMM (Ohio Composting and Manure Management) Program is funded by OARDC/OSU.