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The carbon footprints of food crop production
Jonathan Hillier1, *, Cathy Hawes2, Geoff Squire2, Alex Hilton3, Stuart Wale3
and Pete Smith1
 University of Aberdeen, Institute of Biological and Environmental Sciences, School of Biological Sciences, Cruickshank
Building, St Machar Drive, Aberdeen AB24 3UU; 2Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA;
and 3Scottish Agricultural College, Ferguson Building, Craibstone Estate, Aberdeen AB21 9YA, Scotland, UK

      The agriculture sector contributes significantly to global carbon emissions from diverse sources such as
      product and machinery manufacture, transport of materials and direct and indirect soil greenhouse gas
      emissions. In this article, we use farm survey data from the east of Scotland combined with published
      estimates of emissions for individual farm operations to quantify the relative contribution of a range of
      farming operations and determine the carbon footprint of different crops (e.g. legumes, winter and
      spring cereals, oilseed rape, potato) and farming practices (conventional, integrated and organic).
      Over all crops and farm types, 75% of the total emissions result from nitrogen fertilizer use (both
      organic and inorganic) – from production, application, and direct nitrous oxide emissions from the soil
      resulting from application. Once nitrogen is accounted for, there are no major differences between
      organic, integrated or conventional farming practices. These data highlight opportunities for carbon
      mitigation and will be of value for inclusion in full life cycle analyses of arable production systems and
      in calculations of greenhouse gas balance associated with land-use change.

      Keywords: agriculture, carbon footprint, greenhouse gas, mitigation, N-fertilizer

Introduction                                                         contribution to GHG emissions in carbon equiva-
                                                                     lents (CE) of many human activities. The agricul-
Increasing population, industrialization and conse-                  ture sector is one which contributes significantly
quently energy use have led to a 10-fold increase in                 to the global carbon emissions, through the pro-
the global energy budget since the start of the                      duction and use of farm machinery, crop protection
twentieth century (Boyle, 2004). Atmospheric                         chemicals such as herbicides, insecticides and fungi-
CO2 levels have increased from a pre-industrial                      cides, and fertilizer. The latest UK Greenhouse Gas
value of around 280 ppm to 379 ppm in 2005                           Inventory estimates the proportion of the nation’s
(IPCC, 2007). Since 1979, land temperature has                       overall carbon footprint due to agriculture to be
increased by around 0.258C per decade and sea                        around 8%, 75% of which is directly related to fer-
temperatures by around 0.138C, and are projected                     tilizer use (Choudrie et al., 2008). However,
to increase by 1.1 to 6.48C by 2100 (IPCC, 2007).                    detailed studies into the contribution of specific
   Concerns about greenhouse gas (GHG) emissions                     farming activities during crop production to the
and their effect on global warming have inspired the                 overall footprint are only recently being conducted
quantification of the carbon footprint, i.e. the                      (e.g. Adler et al., 2007; St Clair et al., 2008).
                                                                        Efforts at quantification have become increas-
*Corresponding author. Email:                   ingly important since the introduction of biofuel

                       # 2009 Earthscan. ISSN: 1473-5903 (print), 1747-762X (online).

and biomass crops as alternatives to fossil fuels.          products and machinery. Combining this with
Quantification of the carbon balance of such crops           additional data from Koga et al. (2003), St Clair
compares the carbon cost of inputs and practices            et al. (2008) recently developed a simple method-
with the benefits of displacing carbon released by           ology for calculating emissions associated with con-
fossil f
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