Agriculture Reference
In-Depth Information
greater N excretion and thus greater ammonia
emission (Table 10.3). Better N utilization was
maintained throughout the year with perennial
grassland, which reduced nitrate leaching and
denitrification losses by over 50%. More com-
plete year-round ground cover also reduced sedi-
ment erosion and runoff loss of P, and greater
use of grass allowed a whole farm balance of the
major nutrients. The elimination of maize har-
vest operations reduced the energy footprint by
about 25%. Greater fibre intake by the animals
increased enteric methane emission by about
10%. This increase in methane emission along
with the reduction in energy use provided a
small increase in the carbon footprint of beef
production. This change in crop management
was of benefit to the producer reducing annual
feed costs and increasing farm profit by over
US$140 per cow.
Many different cropping strategies can be
used to provide feed in livestock production, and
any given strategy can have both positive and
negative environmental impacts relative to other
options. This diversity makes this type of evalua-
tion specific to the farm or production system
being evaluated, and general conclusions can-
not be made. Reduced tillage operations and the
use of cover crops will normally be beneficial for
water quality, but they may or may not be of
benefit to air quality or of economic benefit to
the producer. Greater use of perennial grassland
will normally benefit most aspects of water
quality, but there may be trade-offs for air qual-
ity and carbon footprint. The economic costs
and benefits of grassland and controlled grazing
are greatly influenced by the size and type of
livestock operation.
nutrients is of greatest concern, so greater
amounts of gaseous emission may be tolerated
if this can lead to better water quality. In the
drier climate of the western US, air emissions are
often of greater concern than surface runoff.
Ultimately though, strategies are needed that
benefit both air and water quality while main-
taining profitable livestock production systems.
The farm is only a piece of the whole system
of pollution and the management required to
reduce pollution. As nutrients leave the farm,
they affect groundwater, surface water and air
beyond the farm. Because groundwater moves
relatively slowly, groundwater pollution is typi-
cally noticed locally where drinking water from
wells can be affected within several kilometres of
the farm. Surface water affects a larger area,
normally defined as the watershed, consisting of
streams and water bodies used for recreational
purposes as well as drinking and fishing. Gaseous
emissions such as ammonia affect the airshed of
the region. Airsheds are not well defined as they
are influenced by wind speed and direction, and
the topography of the region. Pollutants enter-
ing the air may travel great distances and trans-
form in the atmosphere before they are deposited
back to the earth. Greenhouse gases remain in
the atmosphere for many years raising atmos-
pheric concentrations, which are believed to be
affecting climate change. These effects reach far
beyond the region, affecting global atmospheric
Watershed evaluation
Watershed boundaries can be accurately defined
to track the flow of water toward streams, rivers
and larger water bodies. Watershed models are
often used to evaluate the impact of changes in
agricultural management at the watershed out-
let by simulating nutrient losses from agricul-
tural land and the transport of those nutrients
through the watershed. Two commonly used
watershed-scale water quality models are the
Annualized Agricultural Non-Point Source
Pollution Model (AnnAGNPS) (Bingner and
Theurer, 2012) and the Soil and Water
Assessment Tool (SWAT) (USDA-ARS, 2012).
Processes occur during stream flow, which
transform and filter nutrients, so the quantity
and type of nutrients leaving the farm are not
Beyond the Farm
As just illustrated, farms can create a number of
environmental impacts to both air and water
quality. There are often trade-offs when mitigat-
ing these impacts such that reducing one air
pollutant may increase another air or water pol-
lutant. The pollutant of most concern will vary
among regions, so some type of prioritization
among pollutants may be required when select-
ing mitigation strategies. For example, in many
regions in the eastern USA surface runoff of
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