Agriculture as a whole contributes 7 per cent. of all UK greenhouse gas emissions and 14 per cent. globally, but less than 1 per cent. of carbon dioxide. Emissions of carbon dioxide attributed to agriculture arise from direct energy use such as the use of diesel in tractors, gas in heating greenhouses, and electricity used in livestock buildings. The bigger challenge is on two other gases, methane and nitrous oxide, of which some 36 per cent. and 67 per cent. respectively comes from agriculture, livestock, manures, and artificial fertiliser. About 86 per cent. of this methane comes from enteric fermentation in the digestive system of animals (sheep, pigs and bovines), and about 14 per cent. from animal waste. Methane emissions from agriculture have declined by 12 per cent. since 1990.
In December 2006, Defra announced a £750,000 investment in research on ruminant nutrition regimes to reduce enteric methane and nitrogen emissions from livestock. This research project will build on our knowledge-base and take an integrated approach to the development of ruminant nutrition regimes to deliver reductions in total greenhouse gas emissions (particularly methane) per animal and per unit of meat and milk output. Approaches for consideration include the modification of forage-based diets, alterations to concentrate feed formulation and ingredients, and feed supplements. All options and solutions will be looked at.
This research builds on a wealth of past work where Defra and its predecessor have invested in research to improve the productivity of dairy cattle. The resulting increases in individual cow milk yields can reduce methane emissions per unit of milk produced. The Defra research has included, for example, developing grass varieties that are high in sugar and lead indirectly to a reduction in methane emissions.
The Government are also reviewing its approach to anaerobic digestion (AD), a system which, when used in agriculture, processes animal manures and food wastes, and generates methane (biogas) which can be captured and used as a renewable energy source. This technology reduces methane emissions from manures when the methane is captured effectively. Defra is investing in research at the Institute for Grassland and Environment Research looking at how AD technology can be embedded into farming and agricultural systems to deliver a wide range of benefits, including methane mitigation. This research is being done in conjunction with a large EU-funded project looking at the optimisation of AD technology.