Date of Case Study: 2012
Farm Name: Shimpling Park Farm
Location: Bury St Edmunds, Suffolk
Enterprise: Arable (Wheat, Barley, Oats, Spelt and Quinoa) and Sheep
Farm Size: 645 hectares
Soil Type: Chalky Boulder Clay
Total annual carbon emissions 1,150 tonnes CO2e Total annual carbon sequestration 454 tonnes CO2 Total carbon balance (emissions) 696 tonnes CO2e Emissions per hectare 1.08 tonnes CO2e Emissions per tonne of product 0.45 tonnes CO2e.
Note: CO2 stands for Carbon Dioxide, CO2e stands for carbon dioxide equivalence – i.e. other greenhouse gases are included, but converted to a standard unit to represent the global warming impact of carbon dioxide
Total carbon emissions amounted to 1,150 tonnes CO2e.
The main sources of emissions came from Fuels (33.5%) – mostly diesel use, and Fertility (54%) – including nitrous oxide emissions from crop residues and green manures.
This mostly came from diesel use in tractors and combines (29%). There is also diesel used in road vehicles for the farm business. This is to be expected in a mechanised arable system.
Electricity on the farm amounted to 4% of total emission, mostly used for grain drying. It’s also worth noting that a 50kW array of solar PV panels exports around electricity offsetting 16 tonnes of CO2, as well as providing some ‘free’ electricity to the farm.
It’s worth noting that materials used on the farm, including wood, water, metal, paper and tyres amounted to just 0.1% of total emissions.
Nonetheless it is worth recording these items because embodied energy in concrete and steel in particular can have large carbon impacts on large projects – for instance a new barn, shed or farm roads.
As mentioned above, there is a lot of embodied energy in steel, which is exposed in calculating the impact of farm machinery. In the Farm Carbon Calculator, any machine under 10 years old is accounted for, and depreciated over 10 years.
The manufacture of tractors and telehandlers on this farm amount to 3.7% of total emissions. However if these were all bought in one year and accounted for in one year (not depreciated over ten) then the impact would be 37% of total emissions.
Nitrous oxide emissions from crop residues of arable crops (beans, peas, wheat and oats) contribute to a large percentage of total emissions at 29%. This is due to nitrogen in the crop residue being oxidised in the soil and being released as nitrous oxide.
Leguminous green manures (red clover) contribute a further 17% of emissions through nitrous oxide released during nitrogen fixation. This appears to be a very negative attribute of green manures, however they can also contribute to a substantial increase in organic matter levels, which sequesters atmospheric carbon. In effect this at least ‘balances out’ the nitrous oxide emissions.
Also worth mentioning is the 2.8% of emissions from the application of rock phosphate.
The farm has a herd of 250 sheep, which contribute 6.6% of emissions from methane through the process of enteric fermentation (common to all bovines).
Transport of arable crops to a local mill accounts for 1.3% of emissions. Whilst this is not delivered to the final customer it demonstrates that ‘food miles’ can be only a small part of the issues relating to climate change and food.
Carbon is sequestered in perennial biomass and soils on farms. On this farm 60% of carbon is sequestered in woodlands, whilst permanent field margins (21%) and hedges (18%) are the other main carbon sinks.
The total carbon sequestered on the farm (454 tonnes of CO2) offsets 40% of all carbon emitted by the farm business.
Note that soil organic matter levels have not been sampled – see discussion below.
The major omission to this calculation, due to lack of data, is that soil organic matter levels have not been measured. See below for discussion of this issue. A comprehensive calculation of materials used (e.g. wood, steel, concrete, etc.) was not undertaken due to time limitations. However this was not expected to be a significant source of emissions as a percentage of total farm emissions. An analysis of embodied energy in farm buildings was not carried out, also due to time limitations. This would be worth looking at in future calculations, but it is not considered that emissions from embodied energy in buildings would skew the figures dramatically.
In organic systems a major aim is to cultivate soils in a manner that builds fertility continuously. This should go hand in hand with raising organic matter levels, which also means atmospheric carbon is being sequestered in the soil.
For example a 0.1% increase in SOM on clay soils, per hectare per year, can sequester nearly 7 tonnes of CO2. If this applied to the whole of Shimpling Park Farm then the annual carbon sequestration from soil alone would amount to almost 4500 tonnes of CO2, four times greater than total carbon emissions!
Is this achievable? In the Soil Association paper Soil Carbon and Organic Farming (2009) a comprehensive analysis of studies is made that examines soil organic matter (SOM) levels in farming systems across the world. There was a huge range of results in temperate organic arable systems, from SOM increases of 0.5% per year through to annual SOM losses. However it confirmed that annual SOM gains of 0.1% are perfectly achievable.
Even if annual SOM gains were just 0.025% then on this farm the carbon sequestration in soil would equal all the carbon emissions from the business. Add to this the sequestration from biomass and the farm would have net carbon sequestration.