PARALLEL SESSION 2B: EMISSIONS MODELLING 8 th Int. Conference on LCA in the Agri-Food Sector, 1-4 Oct 2012 177 Modelling N 2 O emissions from organic fertilisers for LCA inventories Matthias S. Meier * , Christian Schader, Alfred Berner, Andreas Gattinger FiBL - Research Institute of Organic Agriculture, Ackerstrasse, CH-5070 Frick, Switzerland  Corresponding author e-mail: matthias.meier@fibl.org ABSTRACT Apart from mineral fertilisers, organic fertilisers act mainly via the soil C-N pool in order to provide available nitrogen to plants. This different mode of action is not reflected so far in the current IPCC N 2 O emission model. Here we propose a simple model to calculate N 2 O emissions from organic fertilisers and plant residues. It considers the long-term immobilisation of N within stable organic matter in the soil as well as the mineralisation of additional N from the soil pool. A first test with field data showed reliable simulations of measured N 2 O emissions. By comparing values generated by our model with values generated by the IPCC model we show that the IPCC model may overestimate emissions from organic fertilisers. Therefore, within LCA inventories modelling of soil borne N 2 O emissions from organic fertilisers and crop residues should consider the different dynamics of N via the C-N pool in the soil. Keywords: soil borne nitrous oxide emissions, agricultural inventory data, organic fertilisers, crop residues 1. Introduction The IPCC model for determining nitrous oxide (N 2 O) emissions from soils (IPCC, 2006) – originally devel- oped for the reporting of national GHG inventories – is widely used within life cycle assessment (LCA) in- ventories to calculate soil N 2 O emissions from agricultural products and processes. This emission factor based model considers the total N input by fertilisation and plant residues to estimate cumulative direct and indirect N 2 O emissions from soils. Regarding direct N 2 O emissions, the model does not differentiate between different fertiliser types, i.e., nitrogen from mineral vs. organic sources including plant residues. However, there is growing evidence that N 2 O emissions from organic fertilisers may be different from emissions from mineral fertilisers. First, from nitrogen-use efficiency studies it is known that mineral and organic fertilisers differ in their mode of action through the way nutrients are transformed in the soil and utilised by plants (Gutser et al., 2005). In organic fertilisers only a fraction of the total N is readily available for plants (as NH 4 + -N and NO 3 - -N). This fraction ranges from up to 85% of total N in poultry slurry down to 0% in compost. The rest of the total N in organic fertilisers is organically bound entering the C-N-pool of the soil where it is released in the mid- and long-term by microbial degradation. By calculating N 2 O emissions based on total N in the IPCC model the different mode of action of organic fertilisers is ignored. Second, 15 N tracer studies with monitoring periods of up to 9 years indicate that N losses from mineral fertiliser are higher than from (organic) crop residue input (Delgado et al., 2010). Again, the higher immobi- lisation of N from crop residues within the C-N-pool is made responsible for the lower N losses during the monitoring period. Using model simulations Delgado et al., (2008) showed that in support with 15 N tracer studies N losses through leaching and N 2 O emissions from crop residue sources are lower compared to min- eral fertiliser. Based on these simulation results they argue that the IPCC N 2 O emission model (IPCC, 2006) overestimates N 2 O emissions from crop residues. Third, Alluvione et al., (2010) measured significantly lower N 2 O emissions from compost compared to urea in corn fields. In this study, N 2 O emissions were only measured during the vegetation period of the crop and therefore, no conclusions can be drawn regarding the long-term emissions resulting from the different fertilisers. Nevertheless, the study by Alluvione et al., (2010) showed that there are measurable differences in N 2 O emissions between mineral and organic fertilisers as well as within different organic fertilisers. Due to the different dynamics of N from organic input sources, different N 2 O emissions from organic fer- tilisers and crop residues compared to mineral fertiliser can be expected. Therefore, N 2 O emissions from organic fertilisers and plant residues should be modelled differently from mineral fertiliser. This is of special relevance when the GWP of crops fertilised mainly or exclusively with organic fertilisers (e.g. from organic farming) are to be compared with the GWP of crops fertilised with mineral fertilisers. We developed a simple model taking into account the different mode of action of organic fertilisers. The accuracy of the model was tested using measured N 2 O emissions from a 3-year study. A comparison of the model calculations from the IPCC N 2 O emission model (IPCC, 2006) was made using data from a long-term field trial at the Research Institute of Organic Agriculture (FiBL), Frick, Switzerland.