Food LCA: agricultural emissions, land use and allocation
Most food impact is created in the field, and it is the hardest part to measure. N₂O emissions, land use change and allocation across joint outputs like milk and meat.
By clca Editorial TeamLast updated
Life cycle assessment of food products differs structurally from industrial products. In a factory the process is measurable, repeatable and controlled. In a field, emissions depend on soil chemistry, weather and management practice, and can vary twofold from year to year.
The three main field emissions
Nitrogen fertiliser application releases nitrous oxide (N₂O) through nitrification and denitrification in the soil. Since N₂O has roughly 265 times the global warming potential of CO₂, even a small percentage of the applied nitrogen can dominate the footprint of crop production.
In ruminant livestock, enteric fermentation produces methane — the largest line in the footprint of milk and red meat. Manure management is a source of both methane and N₂O and varies widely with storage method. In rice cultivation, flooded soil produces methane under anaerobic conditions.
Land use change
The single line that can transform an agricultural product's footprint is land use change. Converting forest to farmland releases carbon stored in soil and biomass, and that release is amortised onto the product over a defined period. For crops such as soy and palm oil, this line can exceed the sum of all others.
Origin traceability is therefore not merely a supply chain matter in food LCA but a direct calculation parameter. The same raw material from certified deforestation-free sources gives a very different result from an uncertified one.
Allocation across joint outputs
Agricultural systems rarely yield a single product. A dairy cow produces both milk and meat; an oilseed yields both oil and meal. How total impact is split across those outputs changes the result substantially.
- Mass-based — simple, but under-burdens a low-mass high-value output
- Economic — based on market price, so results destabilise when prices move
- Biophysical — splits the animal's energy requirement between milk and meat; common in dairy
- System expansion — subtracts the impact of the product the co-product displaces
- The ISO 14044 hierarchy asks you to avoid allocation first, then use physical relationships
Why regional data is essential
The footprint of the same product varies severalfold with the region it is grown in. Irrigation demand, yield, fertiliser intensity and the electricity mix are all regional. Calculating the footprint of a tomato grown in Turkey using Dutch greenhouse data models an entirely different production system.
Tags
- food LCA
- agricultural emissions
- land use change
- allocation
- biogenic carbon
- sector LCA
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