Agriculture Reference
In-Depth Information
Solid manure systems
upon mechanical aeration and turning to
enhance and decrease the duration of the com-
posting process. All of these systems require
a greater investment in manure management
as manure/compost is moved several times and
needs to be mechanically turned or aerated in
some way; in some cases these costs can be pro-
hibitive for on-farm adoption.
One of the major disadvantages of com-
posting raw manures is the loss of N as NH
3
- a
valuable nutrient for crop production and an air
quality concern, as well as a loss of carbon (C),
as carbon dioxide (CO
2
) and methane (CH
4
),
which is a valuable soil conditioner. During the
thermophilic phase (high temperature) of com-
posting, much of the manure N is lost mainly as
NH
3
. Nitrogen losses can range from 3% to 60%
of total initial N (Bernal
et al
., 2009) with the
majority of the N lost during the first 4 days of
composting (Jiang
et al
., 2011). The loss of
organic matter or C has been shown to range
from 9-81% of initial OM depending on the
manure type and bulking agent used (Bernal
et al
., 2009) with the greatest loss of C occurring
later in the composting process (Jiang
et al
.,
2011). Countermeasures to reduce the loss of N
during the composting process can improve the
fertilizer value of composts, and several man-
agement options are available. The addition of a
readily available C source such as molasses has
been shown to reduce NH
3
losses as more N is
stabilized in the microbial biomass (Liang
et al
.,
2006). Additives such as zeolite and biochar
have been shown to reduce N losses by up to
52% (Steiner
et al
., 2010; Luo
et al
., 2011).
Fukumoto
et al
. (2011) demonstrated that the
use of struvite precipitation and nitration pro-
motion in the composting process of swine
manure reduced total N losses by 60%.
Vermicomposting
is a process that relies on
earthworms and microorganisms to help stabi-
lize active organic materials and convert them to
a valuable soil amendment and source of plant
nutrients. As the process is mesophilic (moder-
ate temperature) less N is lost during the process
leaving a lower C:N ratio, which improves its
value for agricultural uses (Lazcano
et al
.,
2008). Due to the lower composting tempera-
ture, manures do not undergo thermal stabiliza-
tion that eliminates pathogens. Therefore, one
potential drawback to the use of vermicompost-
ing for treating animal manures is the presence
Depending on the type of livestock raised and
the production system, a large percentage of on-
farm manure may be handled as a solid.
Production systems that produce mainly solid
manures are broiler and turkey operations, beef
feedlots and dry-lot dairies. In addition, solid
manures can enter the system via solid separa-
tion of slurries and liquid manures. As the mois-
ture content in these manures tends to be low
they are good substrates for composting, pellet-
ing and for use in thermochemical conversion.
The need to move nutrients off farm has
resulted in much interest in
composting
manures
to reduce bulk, concentrate nutrients, reduce
odour, kill pathogens and weed seeds, and have a
stabilized product for transport (Westerman and
Bicudo, 2005). In addition, composting manure
has also been shown to degrade antibiotics effect-
ively thereby reducing the potential for transport
following land application (Kim
et al
., 2012;
Selvam
et al
., 2012). The composted material is
more uniform and easier to handle than raw
manure, providing a source of slow release
nutrients and therefore has commonly been
used for years on many production facilities.
There are several methods for composting
manures: passive composting, aerated compost-
ing, windrow composting, in-vessel composting
and vermicomposting. Passive composting is
probably the most common method used today
because it involves simply stacking manure (and
other feedstock) and leaving them to compost
over a long period. Very little, if any, activity is
performed on the pile once it has been con-
structed. Aerated static pile composting modifies
the passive composting technique by using blow-
ers to supply air to the composting manure. This
process does not involve turning and/or agita-
tion of the piles. Electronic feedback controls are
often used to monitor the pile temperature and
control the operation of aerating blowers.
Windrow composting is similar to passive com-
posting although the piles of manure are turned
or aerated by mechanical equipment to main-
tain optimum conditions. Manures are placed in
long rows and are mechanically turned at fre-
quent intervals in the composting process.
In-vessel composting refers to any type of com-
posting that takes place inside a structure, con-
tainer or vessel. Each type of vessel system relies
