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Discipline: carbon footprint; Keywords: production systems, milk yield, fertilizer use, manure management, rumen fermentation.
Every sector has to limit or reduce carbon emissions. This is the obligation and commitment of countries that signed the Kyoto protocol with different targets set towards 2050. In the UK the Climate Change Act, 2008 stipulates an 80 % overall reduction in greenhouse gasses (GHG) from 1990 levels. The target by 2020 is 11 % and this is the target that the UK Dairy Industry also set itself. For that purpose it was necessary to establish a baseline to work from and therefore DairyCo was tasked to calculate current levels of emissions on UK dairy farms. Dairy farms were targeted because 85 to 90 % of GHG emissions are attributable before the farm gate. The report of DairyCo with title: Greenhouse gas emissions on British dairy farms, dated February 2012 is available from their website www.dairyco.org.uk.
In the study DairyCo analysed 415 dairy farms which reflected a range of production systems, farm types and geographical distribution across the UK. Data collected were average milk yield per cow and total annual milk yield corrected to 4 % butterfat, concentrate feed used, proportion of the year animals are on pasture, quantity of fertilizer used, herd replacement rate and manure management system, in addition to managerial information, fuel and electricity use and a few miscellaneous items. The average GHG emission for the 415 farms, expressed in gram (g) carbon dioxide equivalents (CO2e), was 1309 g CO2e per litre of fat-corrected milk, with farms varying from 832 to 2808 CO2e per litre. The large variation between farms suggests much scope for improvement, meaning reduction potential of GHG. Interesting is the estimate which I calculated for commercial dairying in South Africa of 1300 to 1500 g CO2e per litre milk,based on limited information.
The percentage contribution to the GHG emission per litre milk was: enteric from rumen fermentation 40 %, manure 6 %, nitrous oxide from pasture fertilisation 10 %, artificial fertilizer 8 %, feed use 26 %, fuel 3 %, electricity 3 % and other (bedding, lime, sprays etc.) 4 %, showing that rumen fermentation and the feed provided to the herd carry the bulk of the emissions. The following findings and comments serve to also provide directives for local dairy farmers:
Carbon footprint and milk yield per cow: Methane emissions from rumen fermentation per litre milk are lower in higher yielding cows, as the emissions attributed to the herd are spread over a larger volume of milk. Higher milk yield of course also goes hand in hand with better efficiency.
Carbon footprint and feed use: Feed use in the carbon footprint model is calculated as all feeds (concentrates, bought in feeds, home-grown feeds and by-products) divided by the litres of milk produced. Some bought in feeds such as soya and maize have a high carbon emission factor due to the imputed land use change associated with its production. On the other hand, feeding certain by-products can reduce the carbon cost of the diet. This is because the bulk of the carbon cost is attributed to the human food chain. Bran, hominy chop, DFG and brewers grains are examples. Furthermore, optimising feed conversion efficiency (by selecting for cows requiring less feed per litre milk) and providing cows with high quality, highly digestible roughages help to ensure efficient utilisation of the diet and reduced rumen methane production; so does increased dietary starch, but care must be taken not to overfeed due to implications to rumen health and animal welfare. Utilising more home-grown roughages will help reduce the amount of purchased feeds required, thereby reducing costs and carbon footprint.
Carbon footprint and fertiliser use: This is more of a concern in pasture-based systems. Higher rates of nitrogen application increase the carbon footprint per litre milk. Reliance on artificial fertiliser can be reduced by better nutrient planning and management and more efficient use of manure and slurry.
Carbon footprint and herd replacement rate: Reducing herd replacement rate has a direct effect on carbon footprint per litre milk, as emissions are offset over a longer productive life. Replacement rate can be improved by commitment to optimum herd health and welfare, targeting problems such as lameness, mastitis and fertility. These factors are of course also linked with improving milk yield, further helping to reduce carbon footprint per litre of milk. By calving heifers between 22 and 24 months of age means that fewer young animals are required and carbon emissions associated with the rearing period are reduced. The benefits of calving heifers down earlier are not just environmental, there are also proven economic advantages to the business.
Carbon footprint and electricity and fuel use: This is a comparatively small component of a farm carbon footprint but since it can be controlled by the farmer, it offers an easy way to limit the carbon footprint. The assessment showed that milking, milk cooling and plant washing were the areas that provided the greatest potential electricity reductions; which incidentally also apply to reducing the water footprint. Reductions in fuel use are a matter of discretion. Another avenue that can be pursued for large herds is utilisation of methane for electricity requirements. This requires investment in a capture and generating plant.
Bottom line: The study showed that there are no new or difficult-to-achieve things that the dairy farmer needs to do to limit carbon emissions. Those things that advisors keep on saying and commitment to good management, animal health and improved efficiency and milk yields will be the primary factors towards a reduced carbon footprint. However, in general, we need a similar study in South Africa to the one conducted by DairyCo, to establish our baseline figures and variation between farms.