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
Table 1. Comparison of model calculations.
Conventional tillage Reduced tillage
N2O
sionsemis-
based Difference on
N2O
sionsemis-
based Difference on
N2O emissons
based on new
on
2006
IPCC
model
the basis of
IPCC model
N2O emissons
based on new
on
2006
IPCC
model
the basis of
IPCC model
Crop rotation model [kg/ha] [kg/ha] in [%] model [kg/ha] [kg/ha] in [%]
Winter wheat 3.52 3.80 -7 2.96 3.69 -20
Sunflower 2.26 2.44 -8 1.96 2.45 -20
Spealt 2.88 3.11 -7 2.89 3.43 -16
Clover grass 3.16 3.48 -9 2.62 3.60 -27
Clover grass 5.66 5.93 -5 5.50 6.32 -13
Silage corn 1.21 1.42 -15 1.88 2.86 -34
Winter wheat 1.93 2.14 -10 1.65 2.28 -28
Average -9 -23
4. Discussion
Our model presented in Fig. 1 reflects the nature of organic fertilisers considering its predominant mode of
action via the soil C-N pool. By integrating the coupled biogeochemical cycles of C and N, nitrogen immobilisation
and mineralisation are included in the N2O emission calculations. Different organic fertilisers are
differentiated in the model by the fraction of available N, organically bound N, and the C content. Other
characteristics of organic fertilisers such as the liquid phase in the case of slurry are not considered in the
model. Even though due to its liquid phase slurry might enhance denitrification and by that possibly leads to
higher N2O emissions. However, compared to solid organic fertilisers this characteristic of slurry might be of
significant difference in the first period after application only. Our model calculates long term N2O emissions
from annual N inputs where such short-term effects are interfered with climatic conditions such as temperature
and precipitation. Site specific climatic conditions can be considered in the model by using site specific
emission factors.
A first test with measured N2O emissions shows a high correlation to the N2O emissions calculated by our
model (Fig. 2). Different fertiliser treatments including mineral fertiliser and plant residues only were reliably
calculated. The reason for the fact that the model didn’t reproduce the exact measured values is because
we used the default IPCC emission factors (IPCC, 2006). Using site-specific emission factors the model will
produce the measured values with high accuracy.
In cases where there is a build-up of SOC like under reduced or no-tillage cultivation practices combined
with high organic matter input through organic fertilisers and crop residues our model calculates lower N2O
emission due to a higher long-term immobilisation of N (Table 1). There are studies, though, that show
higher denitrification activities under reduced or no tillage cultivation practices than under conventional tillage
resulting in higher N2O emissions (Palma et al., 1997; Steinbach and Alvarez, 2006). However, the
meaning of such studies for long-term emission patterns under reduced or no-tillage management are still
unsure and discussed controversially (Mummey et al., 1998; Six et al., 2004; Steinbach and Alvarez, 2006).
In a meta-analysis Steinbach and Alvarez (2006) found in Pampean agroecosystems increasing N2O emissions
under no-till. The authors conclude that the mitigation potential of no-till due to C sequestration might
be overcome in about 35 years. In contrast, Six et al., (2004) showed in a literature review analysing studies
that compared no- and conventional tillage, N2O emissions seem to increase in newly converted no-tillage
systems but over a period of 10 years in humid climates and a period of 20 years in dry climates N2O emissions
decrease and overall net GWP is reduced under no-tillage cultivation practices. Further, in cases where
there is a build-up of SOC our model would also deliver lower N2O emissions for mineral fertiliser applied
under reduced or no-tillage cultivation practices due to immobilisation of N from crop residue decomposition.
5. Conclusion
Our model-simulations support earlier findings that the IPCC model overestimates N2O emissions from organic
fertilisers in certain cases. However, our model has to be further validated with field measurements of
N2O especially under cultivation practices that result in a build-up of SOC.
By including N mineralisation and immobilisation in N2O emissions’ calculations our model reflects field
situations with higher accuracy than the IPCC 2006 model. It accounts for the different dynamics of N from
organic fertilisers and crop residues. By including the C cycle, which is influenced by climatic conditions,
soil conditions, and management practices, factors beyond the N input influencing N2O emissions are also
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