What’s your carbon footprint?
Jerry Alford looks at the thorny issue of greenhouse gas emissions from livestock and ways that you can reduce your carbon footprint
There has been a lot of comment recently about greenhouse gases and carbon footprints, and in particular the poor performance of ruminants. There is no doubt that this is a one-sided view of something more complex, and we need to acknowledge the ability of cattle and sheep to produce highquality products we can utilise, such as
Three GHGs in particular result from livestock in the UK: carbon dioxide, methane and nitrous oxide. Carbon footprint calculations can be complex, so a figure of carbon dioxide equivalence is used (CO2e per unit). All of the inputs and outputs have to be included, including transport and production of inputs, such as fertilisers. It’s also important to note
Strategies to reduce the carbon footprint of ruminants are tricky as we often end up substituting one gas for another the units being compared, for example kg CO2 per tonne or hectare, per kg wool, milk and meat, from a low-quality food source that we cannot – grass. Livestock also play an important role in maintaining biodiversity and provide an essential conservation tool for habitat management. Although there are many more sources of emissions than farming, it is an area that we need to be aware of and, where possible, take action.
Greenhouse gases A carbon footprint is defined as the total greenhouse gas (GHG) emissions caused by an individual, event or product. These greenhouse gases are associated with global warming. Greenhouse gases differ in their global warming capacity – for example, methane is a far more potent GHG than carbon dioxide – so each gas is given a greenhouse gas potential value.
live weight gain or per head. Therefore, standard protocols are being developed for more accurate comparisons. Additionally, we need to be aware that other gases are involved, for example, ammonia is not a GHG, but is a source of nitrous oxide.
Carbon sequestration This term is commonly used, and is often seen as a benefit of grazing cattle. It refers to the build-up of carbon in the soil. It can be influenced by the system but it also depends on the starting point. Arable land converted to long-term grass will sequester organic matter, but long-term grazing may already be at a point where losses are balanced by inputs.
Biologically, carbon can be added to the soil in two ways. Firstly, through physically adding materials such as straw, composts,
roots and uneaten or trampled vegetation. Secondly, through photosynthesis, in particular carbohydrate exudates from plants roots that feed soil life. Soil bacteria and fungi release carbon dioxide and nitrous oxide, so there is always a process of uptake and release.
Tackling your carbon footprint Ruminant emissions Livestock contribute to greenhouse gas emissions in two ways, through rumen fermentation and their manure. We cannot stop ruminants producing methane, and although there is some research (including an Innovative Farmers trial on biochar), there is currently little evidence that anything we feed can do so. Losses from manure can be offset when it is applied to grass, as it contributes to increased grassland yield and improved storage of soil carbon (see below). Strategies to reduce the carbon footprint of ruminants are tricky as we often end up substituting one gas for another. For example, adding cereals to the diet reduces methane production, but increases nitrous oxide and carbon dioxide emissions, because of the fertiliser and cultivations involved in cereal production, while silage and hay-making are sources of emissions too. Manure is a source of methane, particularly from stores where methane is released due to anaerobic digestion. Dung
44 Organic Farming Spring 2019