The Australian Government plans to reduce greenhouse gas emissions in Australia by putting a price on carbon emissions and other measures such as the Carbon Farming Initiative and renewable energy targets.
Dairy farms have several emission sources e.g. a 330 cow that grazes pasture (56%) and has supplementation (44% grain), the farm will have total emissions of approximately 2,120 tonnes of CO2e (carbon dioxide equivalent) per year. This will consist of 55% methane and 18% nitrous oxide on-farm emissions plus 18% embedded emissions in inputs i.e. bought in feed, fertiliser and chemicals and 8% from on-farm energy use.
Methane production in the rumen of dairy cows is strongly associated with the digestion of forages, so high energy supplements (e.g. grain), or the use of fully mixed rations reduces methane per litre of milk. As a result, there is roughly 30% difference in emissions intensity between the two extremes of dairy systems – fully pasture fed (~17.5 t CO2-e/t milk solids) or fully lot fed (~12.5 t CO2-e/t milk solids).
Under current rules farmers are not accountable for the on-farm emissions (i.e. methane and nitrous oxide). The embedded emissions in farm inputs are accountable at the point of manufacture. Energy use (electricity and fuel) is accountable by the energy generator or the fuel refiner. With a price on carbon emissions the energy generator or fuel refiners will increase prices in order to pay for their emissions.
Dairy Australia and partners have been working hard to understand the avoidance (abatement)options for reducing farm emissions and some ‘possibilities’ are listed below. There has been no attempt to differentiate possibilities that are currently available from those that are yet to be developed, nor between possibilities that will not be available for support via the Carbon Farming Initiative.
Some dairy farms and feedlots may produce sufficient dairy effluent to trap the biogas produced from a pond system and extract methane for use as an energy source. Capturing and flaring the biogas also reduces emissions.
Though not counted as ‘farm emissions’ there is scope for more efficient energy use on some farms, with associated cost savings.
If increased grain feeding and increased nitrogen use (pasture quality) is a strategy for reducing methane, then more off-farm inputs, with a higher overall level of embedded emissions will be needed on dairy farms. On the other hand, production/manufacturing efficiencies in other industries could reduce the embedded emissions in farm inputs.
Rumen methane production per litre of milk differs across farming systems – under best practice management, the range is from about 6 t CO2-e/t MS (tonnes of CO2e of methane per tonne of milk solids) in a feedlot, to about 10 t CO2-e/t MS in a fully grazed situation with very little supplementation. However, best practice for production efficiency and profit give the best outcome for methane abatement for any particular farming system. It remains to be seen whether the financial incentives to reduce emissions via the Carbon Farming Initiative will be sufficient to drive changes in farming practice.
Currently, well managed dairy farms have few options to reduce methane emissions without changing their farming system. Making changes to reduce emissions would require analysis of the impacts on productivity and profit. Interestingly some innovations which reduce emissions per litre of milk can increase whole farm emissions. For example, if grain supplementation is increased then 3 things tend to happen:
1. pasture consumption per cow goes down,
2. milk production per cow goes up, and
3. stocking rate is increased to take advantage of the extra pasture.
In this example methane per litre of milk falls but methane per cow can rise. The concept applies to the whole industry. An analysis of the US dairy industry showed the high producing cows in 2007 were each producing 66% more CO2e than the low producing cows of 1944 due to the increased feed intake and milk production. However, the opposite was the case per litre of milk, with a reduction from 3.6 kg CO2e/kg of milk in 1944 to 1.35 kg CO2e/kg of milk in 2007.
This means that reducing emissions intensity (emissions per litre of milk) is potentially a win win for the dairy industry – any improvement in productivity and/or production efficiency is likely to give reduction in emissions per litre of milk. However, the national target is to reduce total emissions (as per the Carbon Farming Initiative) and the different way of recording reduced emissions on farm is yet to be resolved.
Nitrous oxide emissions on dairy farms can be up to 25% of total farm emissions but three distinctly different processes contribute to this total:
Current farming systems that are operating at or near best practice management of cows and pastures already minimise N losses and maximise dairy production. If nitrous oxide is to be significantly reduced, new options and strategies will need to be developed and tested.
The extent to which financial incentives (via the Carbon Farming Initiative) offered to farmers to reduce greenhouse gas emissions may change the economics of any of these options remains to be determined
At present the best advice to dairy farmers is to follow current best practice for soil, pasture, fertiliser and herd management as this will minimise greenhouse gas emissions per litre of milk. How these strategies can be applied to reduce methane and nitrous oxide emissions on dairy farms can be explored through the DGAS calculator available on the Dairying for Tomorrow website www.dairyingfortomorrow.com.