Page 64 - Materials Chemistry, Second Edition

50 N. E. Korres

4.2.1 LCA in Agriculture: A Challenging Complexity
Agriculture does not consume resources in a linear sense, as for example, many
industrial processes, and is not therefore a pure ‘‘cradle-to-grave’’ process (Haas
et al. 2000). The same authors argued that the term ‘‘LCA’’ in agriculture could be
misleading since the main agricultural processes are made within a farm and are
based on renewable resources. As they have suggested, ‘‘the term eco-balance used
for LCA in French or German is regarded to fit more accurately.’’
Agriculture LCA has several differences and greater complexity from LCA of
industrial processes, the most important is that agriculture utilizes land and soil.
The balances of soil nutrients such as nitrogen (N), phosphorus (P), and potassium
(K), through fertilizer application and plant uptake, need careful consideration.
Modeling nitrogen dynamics in the soil, for example, requires (1) the quantifica-
tion all N losses and (2) understanding of the interactions between these losses. A
conceptual model which is known as ‘‘hole-in-the-pipe’’ (Fig. 8) (Firestone and
Davidson 1989) depicts the flows of inorganic nitrogen through the microbial
processes of nitrification and denitrification. Nitrogen oxides escape through
‘‘leaks’’ in the pipe which symbolizes the actual nitrification and denitrification
processes occurring in the soil (the size of the pipe is variable mainly due to
varying availability of C and N). The size of the ‘‘holes’’ through which N gases
can ‘‘leak out’’ is determined by soil moisture content, water-filled pore space as
well as by other soil conditions such as pH and temperature.
It becomes obvious that estimating long-term balances requires the use of
simulation modeling, which most probably must be adapted to the local context
considering variations in soil texture, rainfall, altitude, etc.
Many agricultural systems are interlinked and therefore changes to one system,
for example, arable crops used for animal feed or grass silage for animal feed will
affect other systems e.g., animal production systems or bioenergy production
systems. Further complications occur with systems which are included or interact
with other, e.g., as in the case of beef production which is partly derived from the
dairy sector. Hence, there can be difficulties assigning environmental impacts
between various product components particularly when the animals which may be
reared in geographically diverse areas including lowlands and/or highlands
incorporated into the LCA.
In addition, agriculture contributes to GHG emissions by the consumption of
fuel or electrical energy, both directly (i.e., in the operation and maintenance of

Fig. 8 Soil N dynamics (based on Firestone and Davidson 1989)