LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

PARALLEL SESSION 4A: CARBON FOOTPRINT 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
were estimated according to IPCC guidelines 2006 (IPCC, 2006). The N content in applied manure was
measured in the experiment. The diesel and energy consumption was based on the operations in the experiment.
GHG emissions related to diesel and energy consumption was based on data from the Ecoinvent database
(Ecoinvent Centre, 2009).
Direct and indirect emissions of nitrous oxide (N2O) were estimated according to the IPCC guidelines
2006 (IPCC, 2006). N leaching was based on measurements in the experiment as reported by Askegaard et
al., (2011). The greenhouse gas emissions and characterisation factors were based on IPCC 2007 standards
(IPCC, 2007).
2.2 Allocation of environmental burden in crop rotations and soil C change
At the agricultural production stage, the crops are interlinked in the organic crop rotations since the yields
of the sales crops depend on the recycling of nitrogen (and carbon) from the green manure crop through its
effects on soil fertility. Thus, the environmental impacts from the green manure crops need to be included in
the carbon footprint of the sales crops. Two approaches are used in the present paper:
A) Assessment of the full crop rotation: The full crop rotation was assessed as a ‘black box’,
where the emissions where based on all the inputs used for the crop rotation and related to the
total sales crop DM yield from the crop rotation. This approach is represented by the dotted
line surrounding the full crop rotation in Figure 2. Thus, the emissions from the green manure
crop are included, but the carbon footprint result can only be estimated as an average over the
full crop rotation per kg DM.
B) Assessment of single crops: allows to estimate carbon footprint results of the single crops in
the crop rotation (e.g. for spring barley). However, in this approach it is assumed that the environmental
burdens and benefits from green manure crops (incl. soil carbon changes) and catch
crops are divided equally among the other sales crops in the crop rotation on an area basis. The
carbon input and N2O emissions from organic (and mineral) fertilisers were allocated to the
specific crops that received the fertiliser. Likewise, carbon input and N2O emissions from the
above and below ground crop residues from the main crops were allocated to the specific main
crop. The carbon input and N2O emissions from the above and below ground crop residues
from the catch crops and green manure crops were allocated equally on the crops in the crop
rotation on a per hectare basis.
Long-term soil carbon changes were included in the study based on recorded carbon inputs from manure
and estimated above and below ground crop residues (based on measured yields and IPCC guidelines 2006
(IPCC, 2006)) from main crops, catch crops and green manure crops. It was assumed that the conventional
crop rotation would be the point of departure – and thus the relative soil carbon changes from the conventional
crop rotation were estimated in a 100 years perspective. The relative difference relative to the conventional
crop rotation in total carbon input was calculated for each organic scenario. It was then assumed that
approx. 10% of the surplus of carbon would be sequestered (Petersen et al., 2011, Christensen 1986).
2.3 Statistical analysis
Statistical analyses by Proc Mixed were performed using SAS software. The carbon footprint values for
the full crop rotation were estimated for each of the four treatments, three locations, two blocks and three
years. The model included treatment and location as main effects and year and blocks as random effects. The
significant difference between treatments was estimated using the Tukey’s Studentized range test with Pf
0.05 if a main effect or interaction was significant. The carbon footprint results are shown as an average over
the years due to non-significant differences between the three years.
3. Results
The analysis of the full crop rotation showed no significant difference in carbon footprint of sales crops
between the different crop rotations (Fig. 3). The higher N2O emissions from grass-clover in the ‘Mulching’
rotation were counteracted by a higher soil carbon sequestration. The ‘No input’ rotation had lower yields
and a negative soil carbon sequestration, which increased the carbon footprint of the sales crop from this
rotation (Fig. 3).
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