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

PARALLEL SESSION 2B: EMISSIONS MODELLING 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
Cinput is calculated by adding the amounts of C in the organic fertilisers and the C in the crop residues.
Above and below ground crop residues can be determined by using the default factors for crop residue estimation
within Chapter 11 of Volume 4 of the IPCC guidelines (IPCC, 2006). If measurements of either SOC
or CO2 emissions from the soil are available these can be used within Eq. 8. However, measurements of CO2
emissions include CO2 form soil microbial activity as well as from root respiration. Therefore, using CO2
emission measurements within Eq. 8 will result in an underestimation of a gain in SOC if Cinput > Coutput and
an overestimation of a loss in SOC if Cinput < Coutput. If no measurements are available the IPCC guidelines
provide in Chapter 2 of Volume 4 a simple model to estimate annual changes in SOC based on soil type,
climatic conditions and cultivation practices (IPCC, 2006).
The amount of Nimmobilised can be determined by estimating the amount of stable C within the SOC for example
by using the simple model described in Favoino and Hogg (2008). Using this model, a percentage
typical of Northern European areas of 35% of SOC transformed into stable organic matter was used in our
model calculations. Besides climatic conditions this percentage further depends on the soil texture and on
how much carbon is already stored in the soil. For specific cases site-specific values have to be determined.
The amount of Nimmobilised in SOC is then determined by Eq. 9:
Nimmobilised = 0.35 × (Cinput – Coutput) / C:Nsoil where (Cinput > Coutput) Eq. 9
Nmineralised is determined by Eq. 10:
Nmineralised = (Coutput – Cinput) / C:Nsoil where (Coutput > Cinput) Eq. 10
The use of the model is not restricted to organic fertilisers. Of course it can also be used for mineral fertiliser.
In that case Navailable equals the N from the mineral fertiliser and NC-N pool originates from plant residues
only.
Figure 1. Soil N2O emission model for organic fertilisers.
2.2. Model testing
The data set from Ellert and Janzen (2008) monitoring year-round N2O, CO2 and CH4 emissions in different
crop rotations for 3 years in Alberta, Canada was used to test the accuracy of our newly developed model.
Since indirect N2O emissions are not captured by field measurements, only direct emissions were considered
in the model calculations for this test.
One crop rotation in Ellert and Janzen (2008) was legume based with alfalfa-alfalfa-alfalfa-wheat-barley
and a second crop rotation was a N-demanding sequence with corn-wheat-corn-wheat-barley. Emission
measurements started in 2001 when the rotations were in the 3 rd phase and lasted until 2003. In each of the
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