Environmental Burdens of Agricultural and Horticultural Commodity Production - LCA (IS0205)
Title: Environmental Burdens of Agricultural and Horticultural Commodity Production - LCA (IS0205)
Contact: Dr Adrian Williams
As part of the drive towards sustainable agriculture there is a need systematically and holistically to assess the resource use and environmental burdens arising from alternative methods of production of agricultural and horticultural commodities. The technique of life cycle assessment (LCA) enables resource use and emissions arising from various agricultural and horticultural production options in England and Wales to be examined in detail.
The commodities examined in this project are: bread wheat, potatoes, oilseed rape, tomatoes, beef, pig meat, sheep meat, poultry meat, milk and eggs. The system boundary is the farm gate.
All inputs into on-farm production are traced back to primary resources such as coal, crude oil and mined ore. All activities supporting farm production, such as feed production and processing, machinery and fertiliser manufacture, fertility building and cover crops are included. The system includes soil to a nominal depth of 0.3 m. All agricultural systems are defined so that they can continue for an infinite period time – thus weeds cannot be allowed to build up and nutrients in the soil cannot be depleted.
Abiotic resources used (ARU) are consolidated onto one scale based on relative scarcity. Individual emissions, such as carbon dioxide (CO2), ammonia (NH3) and nitrous oxide (N2O), are quantified and aggregated into potentials for global warming (GWP), eutrophication (EP) and acidification (AP).
Interactions between inputs, outputs and emissions are represented by functional relationships derived from process models wherever possible, so that as systems are modified they respond holistically to specific changes. For example, crop yields and nitrogen supply, dairy cow diet formulation and milk yield, and grass productivity, emissions, animal grazing and fertiliser applications are functionally related. Process simulation models are also used to derive the long term outcomes of nitrate leaching, soil, crop type and nitrogen supply.
1. Nitrous oxide is the single largest contributor to global warming potential (GWP) for most commodities, exceeding 80% in some cases. There is the least understanding about the reliable quantification of this emission.
2. Organic field crops and animal products generally consume less primary energy than non-organic counterparts owing to the use of legumes to fix N rather than fossil energy to make synthetic fertilisers. Poultry meat and eggs are exceptions, resulting from the very high efficiency of feed conversion in the non-organic sector.
3. There is much greater variation in the relative burdens of GWP, acidification potential (AP) and eutrophication potential (EP) between organic and non-organic field-based commodities than there is in their energy use.
4. Yields (t/ha) are lower for organic than for conventional production such that for a given amount of output more land is always required for organic production (65% to 200% extra).
5. All arable crops incur smaller burdens per tonne than meats, but all commodities have different nutritional properties and energy requirements beyond the farm, so care must be taken in comparisons.
6. Ruminant meats incur more burdens than pig or poultry meats, but ruminants can derive nutrition from land that is unsuitable for the arable crops required by pigs and poultry.
7. Heating and lighting dominate the burdens of long-season tomato production; adopting combined heat and power (CHP) technology could reduce the primary energy consumption by about 70%.
8. Non-organic, loose classic tomatoes incur the least burdens per tonne of produce (in long-season production) and they increase progressively towards organic, on-the-vine specialist types.
The main burdens of commodity production are shown below for England and Wales. As the market share for organic production is relatively small, these values essentially are for conventional non-organic production. The numbers may differ slightly from those in the published report as improvements have been made in the model since initial publication.
Main environmental burdens of crop production (per t fresh weight) in England and Wales
Primary energy used, GJ
GWP100, t CO2 Equiv. (1)
EP, kg PO4 Equiv.
AP, kg SO2 Equiv.
Land use (Grade 3a), ha
Main environmental burdens of animal production (per t carcass weight, per 20,000 eggs, per m3 milk) in England and Wales
Primary Energy, GJ
GWP, t CO2 equiv.
EP, kg PO4 equiv.
AP, kg SO2 equiv.
Development of the models continues in Defra-funded project is0222.
Accessing the models: The commodity models are written in Microsoft Excel.
1. Williams, A.G., Audsley, E. & Sandars, D.L. (2006) Final report to Defra on project IS0205: Determining the environmental burdens and resource use in the production of agricultural and horticultural commodities. London: Defra.
2. Williams, A.G., Sandars, D.L. & Audsley, E. (2007) Sustainability and environmental burdens of milk and beef production. In: Pullar, D. and Lewin, L., British Cattle Conference , Weston, Shropshire, Holsworthy, Devon: British Cattle Breeders Club, 40-47.
3. Williams, A.G., Audsley, E. & Sandars, D.L. (2006) Energy and environmental burdens of organic and non-organic agriculture and horticulture. In: Anon. What will organic farming deliver? COR 2006, Heriot-Watt University, Edinburgh, Wellesbourne, Warwick CV35 9EF, UK: Association of Applied Biologists, 19-24.