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
Improving estimates of life cycle nitrous oxide emissions from cropbased
food products
Jeremy Wiltshire 1,* , Sarah Wynn 1 , Roger Sylvester-Bradley 1 , Daniel Kindred 1 , Nigel Mortimer 2 ,
Anna Evans 2 , Charlotte Hatto 2 , Onesmus Mwabonje 2
1 ADAS UK Ltd, Battlegate Road, Boxworth, Cambridge, CB23 4NN, UK
2 North Energy Associates Ltd, Watsons Chambers, 5–15 Market Place, Castle Square, Sheffield, S1 2GH, UK
Corresponding author. E-mail: jeremy.wiltshire@adas.co.uk
ABSTRACT
A research project called “Minimising nitrous oxide intensities of arable crop products” (MIN-NO) is addressing the scientific and
practical challenges of minimising nitrous oxide emissions from UK arable cropping, and is exploring improved N2O emissions
factors. The average emission of greenhouse gases (GHGs) for 220 UK wheat crops was 405 kg CO2e t -1 based on the Intergovernmental
Panel on Climate Change (IPCC) Tier 1 method (IPCC, 2006). The N2O contribution to GHG emissions per tonne of wheat
grain was approximately 72%, and the coefficient of variation for fertiliser-related N2O emissions per tonne of wheat grain was large,
at 31.9%. Results suggest that soil organic matter status had a large effect on N2O emissions.
The uncertainty ranges in the IPCC N2O emissions factors gave a range of GHG emissions per tonne of grain that is more than double
the value for the GHG emissions assessed using IPCC default emissions factors.
Keywords: food product, nitrous oxide, N2O, greenhouse gas, crop
1. Introduction
Most non-leguminous arable crops in Northern Europe respond positively to applications of nitrogen (N)
fertilisers. The Intergovernmental Panel on Climate Change (IPCC) provides a method for assessing emissions
of the greenhouse gas (GHG) nitrous oxide (N2O) that occur as a consequence of applying N fertiliser:
at the national scale the default value for applied N lost directly as N2O is 1% (range: 0.3–3%), for all crops
regardless of management practices.
Using this method within the UK, N2O emissions have been estimated to contribute 6.1% (111,640 t N2O)
to the total of GHG emissions, with 78% of all N2O emissions originating from agricultural practices (Mac-
Carthy et al., 2011). In the absence of more specific information IPCC methods and their associated emissions
factors have been adopted for lifecycle analysis at a product scale (BSI, 2011) and, using this approach,
the contribution of primary food production to lifecycle GHG emissions of food products has typically been
estimated at around 50%, sometimes more (Wiltshire et al., 2008). Thus, N2O makes an important contribution
to the lifecycle GHG emissions of food products.
A study in the UK is addressing the scientific and practical challenges of minimising N2O emissions from
UK arable cropping. The project is called “Minimising nitrous oxide intensities of arable crop products
(MIN-NO)” and objectives include the following:
1. To gauge the importance of and variability in N2O emissions associated with crop products;
2. To determine a more robust relationship between N2O emission and the rate of mineral N fertilisers
applied, both during crop growth and from crop residues;
3. Through expert estimation and debate, to identify practices which could lower the greenhouse gas
emissions footprint of arable products such as bread, sugar, oils, peas, chicken, whisky and biofuels;
4. To assess how emissions might be estimated more accurately at farm and at national level.
A key hypothesis being tested in the MIN-NO project is that, because some N2O emissions occur after
crop N uptake, emissions relate to the balance between N supply and N uptake. This hypothesis is supported
by evidence for a non-linear N2O response to applied nitrogen fertiliser in corn crops (Hoben et al., 2011).
Contrary to this, most current GHG accounting methods assume a direct proportionality between N fertiliser
use and N2O emissions from land, as agreed internationally by IPCC (2006). This assumption implies that
large reductions in N fertiliser use and crop productivity are required to minimise the N2O contribution to life
cycle GHG emissions of crop products. However, if N2O emissions were N-balance related, N amounts that
minimise N2O intensities would be similar to current use, and GHG mitigation would be compatible with
sustained crop productivity (Figure 1).
The project objective to gauge the importance of and variability in N2O emissions associated with crop
products, requires collection of multiple field-by-field GHG emissions data to determine variability in onfarm
N2O emissions, and their contributions of to the GHG intensities of arable crop products. In this paper
we present GHG emission assessments for wheat grain from multiple fields, using lifecycle assessment
(LCA) methods, and show the extent of variability in emissions (especially N2O) for the wheat grain product
to help meet objective 1 of the project.
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