Manure is an extremely important resource with many productive uses. Some
of the more important include:
Fertilizer
Well over 95% of all animal manure is used as a fertilizer
for land application. Nutrients found in the manure help to build and maintain
soil fertility, and its economic value is calculated from the availability of
Nitrogen (N), Phosphorus (P), and Potassium (K). Manure must be applied to land
carefully because excess nutrients can harm crop growth, contaminate the soil,
cause surface and groundwater pollution, and waste nutrients.
Composting
Composting is an aerobic microbial treatment of solid manure.
It has the advantage of reducing manure volume and transforming it into a more
stable nutrient form. The organic matter is allowed to decay in a pile or windrow.
When spread on land, nutrients are slowly released into the soil for crop use.
Temperatures above 160 degrees can be generated. Because oxygen is necessary for
composting, the pile should be turned regularly to incorporate the oxygen and
allow composting of the less decomposed material at the edge of the pile. The
nutrients in composted manure are less likely to be transported off site in runoff
and leach into the groundwater.
Litter
Livestock manure can be processed using a solid-liquid separation system. Solid-liquid
separation is useful if the liquids will be irrigated or used for flushing. Solid-liquid
separation reduces odors from storages, reduces size requirements for lagoons,
and allows for easier management and pumping for the holding ponds and lagoons.
Solid-liquid separation is used primarily in dairy liquid manure systems, but
is also used in swine liquid manure units.
Mulch
Livestock manure can be processed into a solid to be used as an off-farm fertilizer,
soil additive, or mulch. Developing a market for this product
can be difficult for farms, depending on their location and the acceptance of
the product by gardeners.
Recycling
Animal waste can be recycled for flushing systems to transport
manure to storage after most of the manure solids are removed.
Biogas Production
Manure mixtures that are treated anaerobically produce biogas
and a stable liquid. Biogas contains about 40% to 60% methane by volume and can
be used to run an engine generator to produce electricity, or can be burned for
heat. The disadvantage is that the gas has a relatively low BTU output (about
600 BTU per cubic foot) and is corrosive to generator engines due to the preserve
of hydrogen sulfide. This process is also very expensive to construct and maintain,
so its use is limited to very large livestock operations..
Solid Fuel
Dried solid manure can be used as a fuel for brooding (providing
zone heat for young birds, livestock, or the incubation of eggs), or it can be
burned to produce energy for other uses.
Settling Tanks
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