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*.
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).
So to get the whole picture we really need to talk about
GLOBAL WARMING POTENTIAL (GWP)
Storage & processing
RetailThe food system
Global Warming Potential (GWP 100 years) kg CO2-Equiv./tonne potatoes at the farm gate
Normalised impact assessment for watercress sourced from the UK (organic and conventional), the USA (organic and conventional) and Portugal (conventional)(Sim et al. 2006)
GWP CO2-equiv (100yrs) per kg of lettuce at the farm gate for 2 UK farms supplying lettuce between January and April.
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 Southern Hemisphere suppliers for the different seasons
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
Soil Organic Matter (SOM)
Root uptake (NH4+, NO3-)
Most uptake as NO3- within plant NO3- reduced to NH4+
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
Nitrous oxide Southern Hemisphere suppliers for the different seasons
(organic and inorganic)
soil organic carbon
1 Gt = 1015g
If these figures are correct UK soils are losing carbon at 13 times the rate of emissions from food imports.
Between 66% and 70% of N2O emissions are derived from soil(IPCC 2000; Bouwman 1990).
English emissions in 2002:
The soil organic content to typical agricultural land is
Relatively small emissions of N2O can exert a strong influence on the total GWP of an ecosystem.
Gaseous emissions from soils differ with:
Effect of temperature on CO Southern Hemisphere suppliers for the different seasons2 emissions
Source: York unpublished
Regional distribution of average emissions of CO Southern Hemisphere suppliers for the different seasons2-equivalents from soils, normalised by the area of agricultural land in the NUTS 2 regions (Freibauer 2003).
Soil Temperature Southern Hemisphere suppliers for the different seasons0C
Soil CO2 Efflux +/- 2 SEM (µmol.m-2.s-1)
Soil CO2 Efflux +/- 2 SEM (ton.ha-1.yr-1)
Time of Day
But it’s more likely to help if….