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Animal production industries have seen substantial
changes over the past several decades, the result of domestic/export
market forces and technological changes. The number
of large operations has increased, and animal and feed
production are increasingly separated in terms of both
management and geography. Concern that these changes
are harming the environment has prompted local, State,
and Federal
policies and programs to control pollution
from animal production facilities.
Trends in Animal Production and
Manure Nutrients
Changes in the structure of livestock and poultry production
are behind many of the current concerns about animals
and the environment. Structural
changes have been driven by both innovation and
economies of scale. Organizational innovations, such
as production contract arrangements, enable growers to
access the capital necessary to adopt innovative technologies
and garner economies of size in their efforts to increase
profits. The significant economic benefits from vertical
coordination, particularly for poultry and swine operations,
have led to both larger operations and greater geographic
concentration of animals.
For example, the number of hog
farms fell more than 70 percent between 1992 and
2004 while the hog inventory remained stable. Larger
farms account for an increasing share of total output.
The average size of U.S. hog farms grew from 945 head
in 1992 to 2,589 head in 1998 and to 4,646 head in
2004. The share of hogs produced on farms with more
than 2,000 head increased from less than 30 percent
to nearly 80 percent. Similar trends occurred in the dairy,
poultry, and cattle sectors.
The innovations and economies of size that underlie
changes in the livestock and poultry sectors also served
to separate animal production from crop production. Large,
specialized facilities today focus on producing animals
and purchase most of their feed from off the farm. This
means there is generally less land on the animal farm
on which to spread manure. The amount
of land per animal unit declined nearly 40 percent
across all animal types between 1982 and 1997, from 3.6
to 2.2 acres per AU (AU defined as 1,000 pounds of live
weight).
Environmental Impacts of Animal Production
The major source of environmental degradation from confined animal production is the wastes (manure, urine, bedding material) that are produced. Animal waste can be transmitted through runoff of nutrients, organic matter, and pathogens to surface water; leaching of nitrogen and pathogens to ground water; and volatilization of gases and odors to the atmosphere. Pollutants may originate at production houses/lots where animals are kept; manure storage structures such as tanks, ponds, and lagoons; or land where manure collects or is applied.
The major pollutants include:
- Nutrients—Nitrogen and phosphorus are essential plant nutrients, but can degrade water quality by causing eutrophication.
- Ammonia—A pungent, colorless
gas that can be a health hazard to humans and animals
at high concentrations, and a precursor for fine particulates
(haze) in the atmosphere. It also contributes to soil
acidification and water eutrophication.
- Hydrogen sulfide—A colorless gas also hazardous to humans and animals.
- Methane—A nontoxic, odorless greenhouse gas.
- Odor—A nuisance associated with animal production facilities. Odorous gases consist of a host of compounds (over 300) that originate from manure in animal housing, manure storage units, and land application.
- Pathogens—Threats to human health that are often contained in manure. Some of the pathogens that pose a threat to human health include the protozoan parasites Cryptosporidium and Giardia and some bacteria species such as Salmonella, E. coli, and Campylobacter.
Manure Production and Excess Nutrients
Two indicators of potential environmental degradation
from animal feeding operations are total nitrogen excreted
and excess nitrogen and phosphorus. Total nitrogen is
an indicator of the potential for both air and water
pollution from the entire operation (production facility,
manure storage, and land application). Excess nutrients
are manure nutrients produced on the farm in excess of
the farm's crop needs. Excess nutrients are susceptible
to running or leaching off the field and into water resources
unless steps are taken to move the manure off the farm
to additional farm land or to other industrial uses such
as energy production or commercial fertilizer production.
In 1997, animal feeding operations controlled 73 million
acres of cropland and permanent pasture. This land was
estimated to have the capacity to assimilate only 40
percent of the nitrogen and 30 percent of the phosphorus
in the manure recoverable from animal production facilities
and available as a crop fertilizer. Large farms, which
constitute 2 percent of the total number of farms, accounted
for almost half of the excess onfarm nutrients.
In 1997, 68 counties had manure nitrogen levels that
exceeded the assimilative capacity of the entire county's
crop and pasture land. Many more counties (152) had surplus
manure phosphorus.
In these areas, it may be difficult to find enough land locally to spread manure without posing a risk to water quality. Research suggests that producers may have to haul manure extended distances in order to apply manure to land at agronomic rates.
Manure's Contribution to Environmental Degradation
While a nationwide study has
yet to be completed, a number of studies have indicated
that animal operations are significant contributors to
water quality impairments in several regions. States
reported to the Environmental Protection Agency (EPA)
in 1996 that animal feeding operations were a contributing
source in 10 percent of rivers and streams reported as
being impaired. A U.S.
Geological Survey (USGS) study of 16 watersheds
found that manure was the largest source of nitrogen
loadings in 6, primarily in the Southeast and Mid-Atlantic
States. USGS
modeling
of total nitrogen and phosphorus export from watersheds
in major water resource regions of the U.S. found that,
nationally, the median contribution of nitrogen from
animal agricultural sources was 14 percent, compared
to 22 percent for commercial fertilizer and 0.8 percent
for point sources (sewage treatment plants, factories).
For phosphorus, the median contribution from animal agricultural
sources was 26 percent, compared to 17 percent for commercial
fertilizer and 3 percent for point sources. The USGS' National
Water Quality Assessment Program found that the
highest concentrations of nitrogen in streams occurred
in agricultural basins, and were correlated with nitrogen
inputs from fertilizers and manure. An analysis of fecal
coliform bacteria in streams found that concentrations
were partly a function of the number of both confined
and unconfined animals in a watershed.
The impact of gases and odor from animal feeding operations
on human health and the environment has been difficult
to determine because data on emissions are generally
lacking. Animal waste in the United States has been estimated
to contribute about 50 percent of all anthropogenic ammonia
emissions, 25 percent of nitrous oxide emissions, and
18 percent of methane emissions.
Water-Air Interactions
Emissions to water and to the atmosphere are not independent events, but are linked by biological and chemical processes that produce various compounds. For example, nitrogen excreted from an animal can follow any number of pathways and enter water as nitrate or the atmosphere as ammonia, nitrous oxide, nitric oxide, or as part of a volatile organic compound. Reducing nitrogen movement along one pathway by changing its form will increase nitrogen movement along a different path.
Reducing Pollutants
A number of practices are available for reducing gaseous emissions and runoff/leaching from animal feeding operations.
- Diet
manipulation
 —Feed
additives and more efficient nutrient utilization
in animals can reduce the amount of nitrogen and
phosphorus in manure. This helps reduce the odor
and ammonia emissions from production houses, and
simplifies manure management for protecting water
quality at all stages of handling and disposal.
- Chemical additive—Different
chemicals can be added to manure during collection
in order to bind nutrients, thus reducing odorous compounds
and ammonia emissions. By reducing atmospheric emissions,
the nitrogen content of manure available for spreading
is higher, increasing its value as a fertilizer. But
the higher nitrogen content can also increase the cost
of applying manure at agronomic rates that protect
water quality.
- Air treatment—Trapping air vented from production
houses and treating it before discharge to the atmosphere
can reduce the release of odorous compounds, ammonia,
and other gases.
- Tank and lagoon cover—Covering storage
tanks and lagoons can greatly reduce the discharge
of ammonia and other gases. Conserving nitrogen in
tank and lagoon waste increases the value of the effluent
as a fertilizer, but can increase the cost of managing
manure to protect water quality.
- Solid-liquid
separation— Separating urea from solid fecal
matter using sedimentation basins or mechanical methods
avoids some of the reactions that cause the formation
of ammonia and odor. Separation also reduces the
cost of moving waste to land for efficient disposal.
- Manure incorporation/injection—Rapidly
incorporating manure into the soil after spreading by plowing or disking—or
injecting manure liquids or slurries directly into the soil—reduces odor,
ammonia emissions, and the potential for runoff to surface waters. However, incorporation/injection
may increase the risk of nitrogen leaching to ground water.
- Comprehensive
nutrient management—Nutrient
management matches the combined nutrient
applications from manure and commercial
nutrient sources to crop needs so
that as few nutrients as possible
are lost to the environment.
An important characteristic of most of these practices is that in reducing one type of emission, they may increase another type of emission. Such interactions can have an important bearing on the design of policies for protecting environmental quality.
Policy Responses
Federal, State, and local governments have responded to the environmental problems posed by animal operations through a variety of regulations and conservation programs (see the chapter on Federal
Laws Protecting Environmental Quality in this briefing
room). The Environmental Protection Agency introduced Clean
Water Act regulations in 2003 for controlling runoff of
manure nutrients from the largest animal feeding operations.
Concentrated animal feeding operations (CAFOs) requiring
a pollution discharge permit must develop and implement
a nutrient management plan that bases nutrient applications
on agronomic rates. This provision requires permitted CAFOs
to spread their manure over a much larger land base than
they are currently using, and most will need to move their
manure off farm. The impact on the livestock and poultry
farms' annual net income depends heavily on the willingness
of local landowners to use manure as a nutrient source.
USDA is using voluntary approaches
(see Policy
Instruments for Protecting Environmental Quality in
this briefing room) such as education and financial incentives
to encourage improved manure handling practices on all
AFOs. Sixty percent of Environmental
Quality Incentive Program funds are earmarked to environmental
concerns on animal operations.
Many States have enacted regulations
that address environmental issues associated with animal
feeding operations (AFOs), including some not addressed
at the Federal level. Some States had manure land application
requirements in place prior to EPA's 2003 regulations,
with coverage often extended to smaller AFOs. Odor is
a persistent local issue, and many States are using setback
requirements to separate animal operations from residential
areas. Ammonia emissions from large animal feeding operations
have prompted California to enact regulations in the
San Joaquin Valley to protect heavily populated areas
downwind.
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