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
(a) (b)
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Figure 1. (a) Effects of N supply on crop production (thin grey line), and on N2O emissions if related directly
to N supply (bold continuous line; as estimated by the IPCC Tier 1 approach) or to the balance between N
supply and crop N uptake (bold dashed line; as hypothesised here). (b) Consequent contrasting effects of N
supply on N2O emission-intensities of crop products for the IPCC (bold continuous line) and our hypothesised
(bold dashed line) scenarios.
2. Methods
Emissions of GHGs have been assessed at an individual field scale for 220 wheat crops, of which 97
crops were grown for the animal feed or distilling markets (feed wheat) and 123 crops were grown for bread
making (milling wheat). The crops were widely distributed across the wheat-growing regions of England and
Scotland, and were grown in the years 2005 to 2011, with more than half of the crops grown in 2010 or
2011.
Data were provided by commercial partners in the MIN-NO project (see Acknowledgements), working
with farmers. To provide the data, the farmers completed a questionnaire, and most received a visit to help
them supply the data from their farm records. Important variables included: crop location, wheat variety,
position in the farm crop rotation, soil type, type of cultivations or tillage, inputs of seed and crop protection
chemicals, fertiliser applications, grain yield, fate of straw, and grain drying.
The GHG emissions were assessed using an LCA approach as given in PAS 2050:2011 (BSI, 2011). The
system boundary was from ‘cradle to gate’, and included production and transport of raw materials (e.g.
seed, chemicals, fertilisers), direct and indirect GHG emissions following application of fertilisers (including
CO2 fixed in the industrial production of urea, and indirect emissions related to NH3 and NOX), and GHG
emissions from machine use and crop drying. The system boundary did not include GHG emissions from the
production of capital goods (e.g. tractors and buildings). The PAS 2050 rules require that agricultural N2O
and CH4 emissions should be calculated with the highest tier approach set out in the 2006 IPCC Guidelines
for National Greenhouse Gas Inventories (IPCC, 2006), or the highest tier approach employed by the country
in which the emissions were produced. The method may be one of three: Tier 1, Tier 2 or Tier 3, which increase
in their complexity and accuracy. We followed the Tier 1 approach (IPCC, 2006), as used to calculate
the latest published UK agricultural greenhouse gas inventory, although this inventory was calculated using
the revised 1996 IPCC guidelines and not the 2006 IPCC guidelines.
The IPCC Tier 1 methodology is simple and generalised, due to its intended initial wide scope of application.
For example, the default emissions factor for direct soil emissions is 1.0% of total N applied lost as
N2O-N; and that for indirect N2O losses following nitrate leaching is 0.75% of leached N lost as N2O-N.
These emissions factors have large uncertainty ranges: for direct soil emissions the range is 0.3 to 3.0%; and
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Crop production,
t ha -1
N-supply-related
emissions, ha -1
N-balance-related
emissions, ha-1
Difference between soil-available N
and the economic optimum N supply, kg ha -1
Emission intensity,
tonne -1 product
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Difference between soil-available N
and the economic optimum N supply, kg ha -1