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Presented at: Carbon Footprint Supply Chain Summit, 24-25 May 2007, London. Identifying and managing emissions from farms and food chains. Gareth Edwards-Jones Georgia Koerber Liz York Llorenç Milà i Canals* University of Wales, Bangor University of Surrey*.

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identifying and managing emissions from farms and food chains

Presented at:

Carbon Footprint Supply Chain Summit, 24-25 May 2007, London

Identifying and managing emissions from farms and food chains

Gareth Edwards-Jones

Georgia Koerber Liz York

Llorenç Milà i Canals*

University of Wales, Bangor

University of Surrey*

Contact: [email protected]

key messages
Key messages
  • Lack of knowledge
  • Complexity
  • We can assume ‘too much’

Based on on-going research ‘Comparative assessment of the advantages and disadvantages of growing fruit and vegetables in the UK and overseas’ funded by the UK Research Councils’ Rural Economy and Land Use programme (RELU).

  • Definitions
  • Different ways of estimating ‘carbon footprint’
  • Commercial relevance of these different measurement methods
  • Overview of agricultural emissions and what it means
  • What does this mean for business and the planet?
carbon is not the only cause of climate change
Carbon is not the only cause of climate change
  • Nitrous oxide (N2O) : 1kg = 296 kg CO2-eq/kg
  • Methane (CH4): 1 kg = 23 kg CO2-eq/kg
  • Others include CFCs, halons, methyl bromide, sulphur hexafluoride, halogenated HC, mono/di/trichloromethane…)

So to get the whole picture we really need to talk about


the food system
















Storage & processing










The food system
the lca for inputs to potatoes in uk
The LCA for inputs to potatoes in UK

Global Warming Potential (GWP 100 years) kg CO2-Equiv./tonne potatoes at the farm gate

  • Fertiliser 42
  • Pesticide 2.5
  • Machinery 5.1
  • Mechanisation 66.4

Normalised impact assessment for watercress sourced from the UK (organic and conventional), the USA (organic and conventional) and Portugal (conventional)(Sim et al. 2006)

lettuce data on measurement v standard
Lettuce data – on measurement v standard

GWP CO2-equiv (100yrs) per kg of lettuce at the farm gate for 2 UK farms supplying lettuce between January and April.

  • Farm 1 – 3.72 kg CO2-equiv
  • Farm 2 – 1.18 kg CO2-equiv

Source: Mila i Canals et al .(2007a)


Primary energy use per kg of apples from European and Southern Hemisphere suppliers for the different seasons

(Mila i Canals et al .2007b)


Removal in crops and animal products

NH3 clings to water droplets, eventually resulting in acid rain. Fossil fuel combustion including the Haber-Bosch process has caused 6-7 fold increase in NOx flux to the atmosphere

Clovers and Lucerne leave 150-200 kgN/ha, Peas and beans leave 20-50 kgN/ha nitrogen.

Rainfall (NH4+, NO3-)

Fertilisers, manures, plant residues

Biological fixation (N2)

Nitric acid is formed from water droplets and N2O, process of wet deposition. Dry deposition is oxides sticking to soil and plants, accounting for 20-60% of total acid deposition.

Rothamsted quote crop residues with nitrogen content < 1.2-1.3% (C/N=30) causes Immobilisation of soil or fertiliser N. > 1.8-2% (C/N=20) results in Mineralisation

Gaseous loss (NH3, N2O, N2)


Nitrate-enriched groundwater leads to eutrophication.

When annual crop residues are returned to the soil, breakdown is normally 70% complete within 12 months

Leaching (NO3-)

Soil Organic Matter (SOM)

Microbial Biomass

NO3- Nitrate

Root uptake (NH4+, NO3-)

Most uptake as NO3- within plant NO3- reduced to NH4+


NH4+ Ammonium


Nitrification involves conversion of ammonium-N 1st to nitrite-N and then to nitrate-N mediated by specific soil bacteria:NH4+ NO2- NO3-

Heterotrophic micro-organisms transform SOM 1st to amino-N and then to ammonium-N

Exchangeable NH4+


Nitrous oxide




Plant material


(organic and inorganic)



organic matter


soil organic carbon


comparative losses in carbon
Comparative losses in Carbon

1 Gt = 1015g

  • The UK’s current industrial CO2 emission is 0.04 G tonnes C per year (and falling) (Bellamy et al 2005).
  • One study suggests that since 1978 UK soil has lost 0.013 G tonnes C per year based on change in soil organic carbon(Bellamy et al. 2005).
  • Therefore, UK soils are losing carbon from soil at one third the rate of industrial emissions.
  • The fuel used to import food and drink to the UK accounts for 0.001 G tonnes C per year(Pearce 2006).

If these figures are correct UK soils are losing carbon at 13 times the rate of emissions from food imports.

nitrous oxide
Nitrous oxide

Between 66% and 70% of N2O emissions are derived from soil(IPCC 2000; Bouwman 1990).

English emissions in 2002:

  • synthetic fertiliser application (27%)
  • leaching of fertiliser nitrogen to ground and surface water (26%)
  • wastes from grazing animals (13%)
  • ploughing in crop residues (13%)
  • manure used as fertiliser (8%)
  • atmospheric deposition of ammonia (NH3) and oxides of nitrogen (NOx) (6%)
  • cultivation of legumes (2%)
  • cultivation of histosols (i.e. high organic content soils) (0.7%)
  • biological fixation in improved grass (0.5%)

(Defra 2004)

soil emissions of nitrous oxide and methane
Soil Emissions of Nitrous Oxide and Methane
  • Applying a typical emission factor of 2.2%, leads to an emission of 6.6 to 13.2 kg N2O-N ha-1(Tzilivakis et al., 2005).
  • Equivalent to CO2 emissions in the range of 3 to 6 CO2-Equiv./tonne/ha

The soil organic content to typical agricultural land is

440 CO2-Equiv./tonne/ha

Relatively small emissions of N2O can exert a strong influence on the total GWP of an ecosystem.

  • UK agriculture emits 873,000 t methane per year.
  • Land fill emits 928,000 t – a lot of this from food waste
  • Cattle responsible for 70% of the agricultural emissions.
  • 87% of total emissions is due to enteric fermentation.
  • Agricultural soils with plenty of oxygen are actually methane sinks.

(Defra 2004)

the public and the green room
The public and The Green Room
  • But to say that soil itself contributes to greenhouse gas should make people either alarmed or sceptical about this report\'s implications..

Jeremy Mason

  • This article is short-sighted, inaccurate, and misleading. To insinuate that the green house gasses from the soil are responsible for environmental degradation is ridiculous.


  • The bit about the gases produced by different kinds of soil seems to me unnecessary for the issue at hand, unless the author is claiming that significant pollution results from our choice of soil. THAT would be news.

Dustin, Philadelphia

variation with emissions
Variation with emissions

Gaseous emissions from soils differ with:

  • Temperature
  • Soil type
  • Soil moisture
  • Crop?
  • Crop management?

Regional distribution of average emissions of CO2-equivalents from soils, normalised by the area of agricultural land in the NUTS 2 regions (Freibauer 2003).

Average emissions of CO2-equivalents per hectare from agricultural ecosystems in Europe (Freibauer 2003).

Soil Temperature 0C

Soil CO2 Efflux +/- 2 SEM (µmol.m-2.s-1)

Soil CO2 Efflux +/- 2 SEM (ton.ha-1.yr-1)

Time of Day

summary so far
Summary so far
  • So the missing element from many carbon footprints so far relates to the absence of measured emissions data – which clearly vary a lot over time and space.
  • But it’s even worse than that…..
key messages for those devising carbon footprints for agriculture
Key messages for those devising carbon footprints for agriculture
  • Need a Systems approach.
  • There is considerable diversity in food production systems and the environments where they occur.
  • Collection of system / site specific data is important.
  • Standard databases will improve with time – but have deficiencies at the moment.
means of achieving carbon neutral food in the food chain
Means of achieving carbon neutral food:in the food chain
  • Renewable energy for manufacturing inputs
  • Energy efficient food transport
  • Energy efficient food storage
  • Energy efficient kitchens
  • Reduce waste
  • Reduce land used in food production and have more ‘wild land’ to act as a carbon sink.
  • Close nutrient cycling loop by putting food waste (and STW) back to land
  • Fewer people?
means of achieving carbon neutral food on the farm
Means of achieving carbon neutral food:on the farm
  • Reduce methane production from ruminants:
  • Reduce emissions of N2O:
  • Reduce emissions of CO2 :
  • Feeding strategies
  • GM
  • Fewer animals
  • Reduce fertiliser use
  • Better timing of fertiliser
  • GM N-fixing crops
  • Reduce cultivations
  • Reduce cultivated area
will carbon accounting save the planet
Will carbon accounting save the planet?


But it’s more likely to help if….

  • The public understand the issues and care enough to use the market to bring about change.
  • Business and Government use the correct science.
  • Scientists communicate clearly and understand the needs of business.