Agriculture is in the rare position of being a contributor of greenhouse gases, but has the capacity to reduce their effects
Climate change is driven by the emission of too many greenhouse gases, which warm the earth up. The main greenhouse gases are carbon dioxide (CO2), methane and nitrous oxide (N2O). The amount of these gases is influenced by human activity, including agriculture, which accounts for 7.5% of all UK emissions.
Carbon dioxide accounts for about 85% of the UK’s emissions. Although agriculture accounted for just 1% of total emissions of the gas, it is a major contributor to the production of methane and N2O.
In 2006 DEFRA estimated that emissions of methane were at 49.1m tonnes of carbon dioxide equivalent (the measure used to calculate greenhouse gas volumes). This amounted to 7% of all greenhouse gas emissions. Each tonne of the gas is calculated to be 25 times more damaging than a tonne of CO2. Encouragingly, the figure was down from 103.5m tonnes CO2 equivalent in 1990, when the gas accounted for 13% of all emissions, but agriculture accounts for 40% of all UK methane emissions.
The other major agricultural greenhouse gas is nitrous oxide (N2O). It is generated through the cultivation of soil, the use of nitrogen fertiliser and emission from manure. Tonne for tonne it is calculated to be 310 times more powerful as a greenhouse gas than carbon dioxide.
In 2006 DEFRA estimated that total UK N2O emissions were at 38.3m tonnes of CO2 equivalent, accounting for about 6% of all greenhouse gas emissions. This was a 40% reduction on the 1990 figure. The reduction in agricultural N2O emissions was 22% in the 16 years to 26m tonnes of CO2 equivalent.
Unlike other industries, agriculture has the ability to capture (or sequestrate) carbon dioxide in the soil or plants so that it does not escape into the atmosphere.
Advice from Farming Futures – a group including the NFU, Agricultural Industries Confederation, DEFRA, the AHDB and the CLA – says that preserving areas of vegetation, such as forest, is important as they absorb carbon. There are opportunities to place these areas in schemes that pay for stored carbon.
Building up the organic content of soil by adding compost and leaving crop residues will also store carbon, while reducing tillage helps keep carbon in the ground and can reduce CO2 emissions by reducing machinery use. Growing energy crops, such as willow or miscanthus, can also capture carbon that can then be converted into energy.
But farmers can do more to reduce the effects of methane and nitrous oxide. Optimising the value of livestock feed will help reduce emissions as well as improve efficiency and keep costs down.
Reducing the exposure of manure and slurries to the open air will keep methane emissions down, while installing an anaerobic digester will convert manures into gas that can be used as an energy source.
Using nitrogen fertiliser, slurries and manures as efficiently as possible will keep nitrous oxide emissions down. Soil testing and field mapping can help target fertiliser applications, while choosing nitrogen efficient varieties or even nitrogen fixing crops will help.