Agriculture Reference
In-Depth Information
concentration, and (2) decreasing atmospheric O
3
formation due to lower CH
4
concentrations
(Fuglestvedt et al., 2010).
In addition, both NO
x
and ammonia (NH
3
) react with atmospheric constituents to form
fine particles (aerosols), considered cooling agents (Forster et al., 2007). Eventually, the NO
x
compounds are deposited on downstream ecosystems in gaseous, particulate, or dissolved
forms, where it undergoes the same fate as other Nr inputs, including potential transformation
to N
2
O, terrestrial acidification and water eutrophication.
NO from agricultural soil is produced by microbial processes, as by-products of
nitrification and products of denitrification, both microbial processes (see previous section)
are strongly affected by N fertilization (Mosier et al., 1998; Robertson & Groffman, 2007),
more broadly NO emissions are also affected by the same environmental and agronomic
factors, including fertilizer application rate and soil moisture. Soil NO can be also produced
by chemodenitrification when HNO
2
spontaneously decomposes to NO. NO produced in soils
is rapidly oxidized to NO
2
in the atmosphere.
NO
x
emissions in some croplands are considered episodic, in some cropped systems the
magnitude of NO
x
emissions can rival those of N
2
O (Matson et al., 1998). Stehfest and
Bouwman (2006) estimated that global NO emissions from cropland and grassland are less
than half of the global N
2
O-N emissions.
L
IFE
C
YCLE
A
SSESSMENT
M
ETHODOLOGY
Life Cycle Assessment (LCA) is a technique used to assess each and every impact
associated with all the stages of a process from cradle-to-grave (i.e., from raw materials
through materials processing, manufacture, distribution, use, repair and maintenance, and
disposal or recycling) (Figure 5). LCA enhances the understanding of how alternative systems
compare with each other, but also how different sub-processes in a system affect the overall
results (Bauman and Tillman, 2004). The environmental performance of the systems studied
is calculated using the LCA-based methodology described in the ISO 14000 series standards
(ISO, 2006a,b). The LCA concept consists of four steps: (1) Goal and Scope definition, (2)
Life Cycle Inventory (LCI), (3) Life Cycle Impact Assessment (LCIA), (4) Life Cycle
Interpretation.
Goal definition and scoping is the phase of the LCA process that defines the purpose and
method of including life cycle environmental impacts into the decision-making process. In
this phase, the following items must be determined: the type of information that is needed to
add value to the decision-making process, how accurate the results must be to add value, and
how the results should be interpreted and displayed in order to be meaningful and usable.
Therefore, the following items shall be considered and clearly described: the functional unit,
the system boundaries, the product system to be studied; the product system boundaries;
allocation procedures; types of impact and methodology of impact assessment, and
subsequent interpretation to be used; data requirements; assumptions and limitations; initial
data quality requirements; type of critical review, if any; type and format of the report
required for the study.
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