Page 132 - Materials Chemistry, Second Edition

Life cycle assessment and agriculture: challenges and prospects

suffice to say, LCA is a useful tool for the comparison of different technological options and 119
systems for producing similar products and services. Indeed, a not unrelated debate is that
between ‘natural’ and ‘synthetic’ materials and products elsewhere in the economic system.
LCA has contributed to debunking the myths around materials such as wool and nylon that
‘natural’ is always best. Semantically, while agriculture provides ‘natural’ alternatives to nylon,
vinyl and other hydrocarbon based compounds, it is also the provider of ‘synthetic’ versions of
various fuels and oils. Hence, the terms are essentially cultural, complex and contextual, and
LCA provides a systematic means by which different delivery systems for similar services can
be evaluated in environmental terms. The same applies to organic, permaculture, urban agri-
culture, genetically modified (GM), nanotechnologies, and so on; if data is available and
impacts can be modelled within uncertainty limits, then LCA is appropriate.
From biodegradable shopping bags to bio-ethanol, agriculture is likely to be increasingly
involved in the transition to lower fossil fuel dependency. The challenge for LCA is to describe
transparently and communicate efficiently the relative impacts of different options in general-
isable terms, to enable effective and appropriate decision-making concerning these new indus-
tries, and to enable the elimination of high-risk, unknown or relatively high impact options in
favour of more benign ones.

9.7.2 What are the key constraints on LCA application to agricultural systems
and how may they be overcome?
The diversity and openness of agricultural systems combined with gaps in data present ongoing
challenges for LCA. For example, the IPCC notes that climate change impacts on agricultural
pests, diseases, crop growth rates and yields, and water availability, are poorly understood
(IPCC 2007). Furthermore, methodological and boundary issues remain. Time boundaries
must be drawn carefully to accurately allocate impact. For example, arable crops are often
grown in rotation and fertiliser applications, and soil nitrification processes link temporally to
both previous and future crops. It has therefore been suggested that impacts should be allo-
cated according to uptake and efficiency per crop, allocating impacts over successive years of
different crops, using cropping plans and developed models of application/uptake of fertilisers
and soil dynamics (van Zeijts et al. 1999). Another ‘timing’ issue relates to land use change. As
indicated above, this is the single largest greenhouse impact of global agriculture, yet as in the
sugar cane case, most agriculture LCA starts from a position of established farming systems.
Since sugar cane in Queensland is long established, LCA does not typically include considera-
tion of ‘one-off’ environmental burdens associated with changes in land use from pre-existing
(natural) systems when this change took place in the past.
Timing is also related to our generally poor understanding of nutrient cycles in agricultural
systems. Agricultural impacts can often hinge on a few poorly characterised inventory entries:
effects of land clearing, fuel use on the farm, fertiliser, water, or N O emissions. The N O emis-
2 2
sions are particularly sensitive due to their potency in climate change (Ehhalt and Prather
2001; IPCC 2006). However, our understanding of the relationship between nitrogen fertiliser
application on crops and resultant fractional increases in soil N O emissions remains relatively
2
rudimentary. In one study, the global climate change impact of extra N O entering the atmos-
2
phere as a result of producing biofuels crops is estimated to equal or exceed the benefits of this
practice in substituted fossil fuels (Crutzen et al. 2007), thus questioning the entire case for
biofuels agriculture (see also Chapter 10). Moreover, this discussion implies a focus on green-
house gas emissions, whereas there are much greater gaps in data availability regarding other
impacts of farming – water, biodiversity, land use and pollution, both in terms of inventory
data and impact factors. This relates to the need for an ‘eco-indicator’ set for Australia as dis-
cussed elsewhere (see Chapter 5). Meanwhile, in the absence of reliable data and impact factors,

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