Page 181 - Materials Chemistry, Second Edition

166 LIFE CYCLE ASSESSMENT HANDBOOK

simple sugars or biomass. The plants, together with photosynthesis, perform
respiration which consists of burning organic matter formed by photosynthe-
sis, with the emission of carbon dioxide to the atmosphere. In addition, the
plants drop to the ground some of its remains, like the leaves, which decom-
pose in the soil and undergo oxidation with formation of carbon dioxide back
into the atmosphere. The process of decomposition of organic matter in soil
can also lead to the formation of complex organic substances, called humus,
which have an important function to absorb water and hold it in the ground.
The plants are the source of nutrients for all other living organisms and thus
feed the food chain, from which the carbon returns to the atmosphere through
breathing, excrement and decay of dead animals. In this paragraph we briefly
consider the carbon cycle as a reminder that it is composed of carbon seques-
tration and emissions, both of these elements need to be taken together into
account and inserted within the system boundaries if a correct calculation of
biogenic carbon balance is to be performed.
For a long time food LCA studies have considered the carbon balance as
net zero, therefore, data about carbon sequestration and emissions along the
life cycle of the product were not included in the boundaries of the study.
Following this approach, however, some positive and negative factors of cer-
tain agricultural practices have not been properly considered. For example,
organic farming or composting increases the soil organic matter, with positive
consequences on biodiversity, but this has not been taken into account and no
effect on the impact categories, such as global warming, was considered. The
same considerations apply to the practices of intensive tillage operation that,
on the contrary, deplete the soil of organic substances. Many studies, there-
fore, currently focus on the verification of the carbon balance, which is no lon-
ger zero, but can be modified depending on which effect overrides the other
(sequestration or emission). Of course, the effect of sequestration prevails in
the majority of studies that follow this approach; therefore, the total carbon
balance is negative (good for the environment).
In our view, if the carbon balance refers to the effects described it is impor-
tant not to report the carbon gain to only the annual cycle of the crop but it
is necessary to consider the land use for 100 years, in line with the character-
ization factor of global warming. This is because many of the practices, that
have a positive effect on carbon sequestration, have an incremental effect in
carbon sequestration which is not infinite or continuous in time. For example,
the transition from conventional farming to organic farming in the early years
increases the organic matter content in the soil; however, this value settles for
all subsequent years and does not increase further. The LCA should therefore
consider the amount of carbon sequestered through agricultural practice and
divide it by 100 years, so that the environmental gain is not assigned just to
one year of observation. The calculation of the increase in the amount of dry
biomass stably incorporated into the plant should follow the same approach.
Moreover, many studies stop at the farm gate; the agricultural stage is often
partially assessed, without accounting for the emissions which occur during
the use of fertilizers and pesticides and the consumer-use phase is often