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
The IPCC method is based on emission factors which take into account a series of farming practices and
land uses. It considers both direct and indirect emissions from managed soils. The IPCC methodology estimates
N2O emissions using human-induced net N additions to soils (e.g. in particular N content in synthetic
or organic fertilisers, deposited manure, crop residues, sewage sludge) (Table 1), or of mineralisation of N in
soil organic matter following drainage/management of organic soils, or cultivation/land-use change on mineral
soils (e.g. Forest Land/Grassland/Settlements converted to Cropland)(De Klein et al., 2006). Residues
amounts were estimated using the shoot to root ratio and harvest index from measured yields for both the
ICC and the CIMAS trial (Giardini, 2001). Nitrogen content of residues was accounted using factors from
literature with measured yields (De Klein et al., 2006; Jensen et al., 2010).
3. Results
Simulation results (Figure 1 and 2) showed clearly that most of the emissions do occur during fall following
residues decomposition. The effect of N fertiliser input is very much limited, considering most of the
emission during spring period laid below 5 g N2O-N ha -1 d -1 . This is the resulting effect of very dry spring
which kept the soil dry (less than 35.2 m 3 m -3 ). Indeed, the peaks following fertiliser application (Abdalla et
al., 2009; Saggar, 2010), which might have been expected during this period, did not occur.
durum wheat
Figure 1. Model results of the analysed period for durum wheat in CIMAS high input system (from previous
crop harvest to the end of the year); vertical lines: full: date of fertiliser application, dashed: harvest dates
faba bean
Figure 2. Model results of the analysed period for faba bean in ICC 50%-GHG system (from previous crop
harvest to sowing of the following); dashed vertical lines: harvest dates
During fall, a series of emission peaks occurred which were due to the coupled effect of residues decomposition
and relatively high soil moisture. This is a common pattern for every crop present in the two trials,
including faba bean plots where no N fertiliser was applied. During fall-winter, rainfall events are more frequent
and intense causing soil moisture to remain high (>20 m 3 m -3 for some sampling dates) allowing denitrification
(Figures 1 and 2).
Results showed that the IPCC procedure estimated higher annual emissions for cereals of 740 g N2O-N
ha -1 y -1 (428 g N2O-N ha -1 y -1 including post harvest periods) on average compared to simulation results and
lower estimation of 304 g N2O-N ha -1 y -1 (609 g N2O-N ha -1 y -1 including post harvest periods) for faba bean
(Table 1). Disregarding crops, the highest difference between CERES-EGC simulations and IPCC estimates
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