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
2. Methods
2.1. Model description
Our model considers the C and N input through organic fertilisers and plant residues brought onto and into
the soil (Fig. 1). A fraction of the total N input (Ntot) is readily available for plants (Navailable) and the remaining
fraction of Ntot is organically bound entering the C-N pool of the soil (NC-N-pool). In contrast to the IPCC
model (IPCC, 2006) where direct and indirect emissions are calculated from total N input our model differentiates
between direct and indirect N2O emissions from Navailable and from the plant available N arising from
the C-N pool of the soil (Navailable C-N pool). Total N2O emissions from managed soils are than calculated according
to Eq. 1:
178
N2Ototal emission = N2Odirect-Navailable + N2Oindirect-Navailable
Eq. 1
+
N2Odirect-Navailable C-N pool + N2Oindirect-Navailable C-N pool
Direct and indirect N2O emissions from Navailable (Loss 1 in Fig. 1) are calculated using the IPCC emission
factors (IPCC, 2006) according to Eq. 2 and 3:
N2Odirect-Navailable = 0.01 × Navailable
N2Oindirect-Navailable = 0.01 × (NH3-Navailable + NOx-Navailable) + 0.0075 × NO3 - -Navailable
Direct and indirect N2O emissions from Navailable C-N pool (Loss 2 in Fig. 1) are calculated using the IPCC
emission factors (IPCC, 2006) according to Eq. 4 and 5:
N2Odirect-Navailable C-N pool = 0.01 × Navailable C-N pool
N2Oindirect-Navailable C-N pool = 0.0075 × NO3 - -Navailable C-N pool + 0.01 × NOx-Navailable C-N pool
For the fate of NC-N pool, which equals (Ntot – Navailable), two pools are differentiated in the model (Fig. 1)
based on a simplified model on sequestration of soil organic carbon (SOC) proposed by Favoino and Hogg
(2008). These two pools differ in their stability of the organic matter with fractions of short-term available C
and N (short-term C-N pool) and stable fractions (long-term C-N pool) where C and N is captured for several
100 of up to a 1’000 years (Nimmobilised) (Favoino and Hogg, 2008). From both pools mineralisation takes
place.
In soils with a build-up of SOC, e.g. through high organic matter input by organic fertilisers and/or conservation
tillage, mineralisation from the long-term C-N pool takes place at a much lower rate than at which
readily available organic matter is converted to stable organic matter (Favoino and Hogg, 2008). In this case
the result is a net capture of N in stable organic matter (Nimmobilised) and therefore, no N2O emissions will result
from this N in the long term. Navailable C-N pool is then calculated by Eq. 6:
Navailable C-N pool = NC-N pool – Nimmobilised
Once the long-term C-N pool is saturated no additional N is captured. Therefore, all N being processed
via the soil C-N pool (NC-N pool) will be available short-term.
In soils with degradation of SOC due to low organic matter input and/or non-conserving tillage techniques
mineralisation outweighs immobilisation. Additional N from the C-N pool is mineralised (Nmineralised).
In this case Navailable C-N pool is calculated by Eq. 7:
Navailable C-N pool = NC-N pool + Nmineralised
Due to the coupled biogeochemical cycles of C and N the amounts of Nimmobilised and Nmineralised can be determined
from the C fluxes consisting of an input flux (Cinput) into the soil, a build-up or degradation of soil
organic carbon (SOC) within the soil and an output flux (Coutput) from the soil. If two of these 3 fluxes are
known the third is determined by Eq 7:
Eq. 2
Eq. 3
Eq. 4
Eq. 5
Eq. 6
Eq. 7
Cinput – Coutput = SOC Eq. 8