The Australian Government plans to reduce greenhouse gas emissions in Australia via putting a price on carbon emissions and by other direct measures such as the Carbon Farming Initiative and renewable energy targets.
Dairy farms have several significant emission sources. If we use as an example, a 330 cow farm that grazes pasture but with a high level of supplementation (56% of the diet as grazed pasture, and 44% as grain), the farm will have total emissions of approximately 2,120 tonnes of CO2e per year. This will consist of about 55% as methane and 18% as nitrous oxide (the so-called on-farm emissions) plus about 18% as embedded emissions in farm inputs (bought in feed, fertiliser and chemicals) and about 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 (eg 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 plans farmers are not accountable for the on-farm emissions (ie methane and nitrous oxide). The embedded emissions in farm inputs are accountable at the point of manufacture and energy use (electricity and fuel) is accountable by the energy generator or the fuel refiner. If there is a price on carbon emissions, that price will be paid by the input providers and added to the price of dairy inputs.
Dairy Australia and partners have been working hard to understand the abatement options for reducing farm emissions and some ‘possibilities’ are listed below. There has been no attempt in the list to differentiate possibilities that are currently available from those that are yet to be developed, nor between possibilities that might or will not be available for support via the Carbon Farming Initiative.
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.
Other abatement options include:
Some large dairy farms and feedlots may produce sufficient manure from dairy effluent to make biogas generation from methane an option.
Though not counted as ‘farm emissions’, there is scope for more efficient energy use on some farms, with associated cost savings.
Not ‘farm emissions’ for accounting purposes and representing a very mixed bag. If increased grain feeding and/or 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 significant changes to their farming or feeding system– making changes to reduce emissions would require analysis of the impacts on productivity and profit.
To make matters more confusing, many innovations that reduce emissions per litre of milk, increase whole farm emissions. For example, if grain supplementation is increased then 3 things tend to happen concurrently – pasture consumption per cow goes down, milk production per cow goes up, and stocking rate is increased to take advantage of the extra pasture. In this example while methane per litre of milk almost certainly falls, methane per cow and per farm can rise.
The concept applies to the whole industry. An analysis of the US dairy industry showed that in 1944 there were 25.6 million dairy cows that produced 53 billion kg of milk. By 2007 US dairy herd had fallen to 9.2 million animals, producing a total of 84 billion kg of milk. The high producing cows in 2007 were each producing 66% more CO2e than the low producing cows of 1944 because of the greatly 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 an associated reduction in emissions per litre of milk. However, the national target is to reduce total emissions (not emissions intensity), and the Carbon Farming Initiative is focussed on reducing total farm emissions and these differences are 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:
1. Indirect emissions, over which the farmer has little or no influence – these include NO2 emissions associated with the ‘production’ of farm inputs such as nitrogen fertiliser or purchased grain, silage or hay. Other than for feedlots, this ‘indirect’ source of NO2 is usually the largest on dairy farms, accounting for up to 50% of total NO2 emissions. Options for dairy farmers to reduce these indirect emissions are very limited.
2. Direct emissions from dung and urine, including those NO2 emissions from deposition of dung and urine on pastures, and those associated with effluent management systems. Options to reduce NO2 emissions from these sources, beyond what would currently be included as normal best practice are relatively limited but are the subject of current research.
3. Direct emissions from the use of N fertiliser. This is the smallest contributor to dairy farm NO2 emissions, often less than 20%. Because of the cost, farmers are already focussed on minimising the losses from fertiliser N, so current best practice is delivering most of the available emission reductions. However, if the use of nitrification inhibitors proves to be effective under Australian conditions, then blanket application of nitrification inhibitors to all N fertilisers during production may be a viable option – if this strategy reduced NO2 emissions from fertiliser by an optimistic 30% annually, then total dairy farm emissions would be reduced by approximately 1.5%.
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.