Understanding emissions on your farm

Dairy farms have several significant emission sources (see the previous section on emission sources). Enteric methane production in the rumen of dairy cows is strongly associated with the digestibility of the diet, so high energy supplements (e.g. grains) or the use of balanced mixed rations (correct energy to protein ratio) improves milk production and dilutes the amount of methane per litre of milk.  Higher quality diets will also reduce the amount of excreta produced, thus reducing methane and nitrous oxide emissions from excreta. 

Here we use two farms milking around the same number of cows as an example of the effect of grain feeding on greenhouse gas emissions. Farm 1 milks 230 cows, feeding 0.7 t of grain per cow/lactation and produces around 380 kg milksolids per cow/lactation. The farm has a total emissions of approximately 1,370 t CO2e and when this is divided by the level of milk production, the emissions intensity is approximately 15.6 kg CO2e/kg milksolids. Farm 2 milks 250 cows, feeding 1.3 t of grain per cow/lactation and producing around 530 kg milksolids per cow/lactation. The farm has a total emissions of approximately 1,780 t CO2e so when divided by their level of milk production, the emissions intensity is approximately 13.4 kg CO2e/kg MS

The first step is identifying the major sources of emissions on your farm – see Identifying your greenhouse gas footprint (below).

  • Identifying your greenhouse gas footprint

    The Australian Dairy Carbon Calculator (previously DGAS) is available for dairy farmers now.

    It allows farm managers and other users to calculate the impact of adopting different abatement strategies on their total farm greenhouse gas (GHG) emissions and GHG emissions intensity and can help them work out the strategies best suited to their farming system.

    Abatement strategies modelled by the calculator fall into four categories; herd management, feeding management, soil management and farm intensification. Modelling shows that any farm efficiency improvement will lower GHG emissions/t MS.

    Five case studies have been developed with latest version of the calculator. The summary of the case studies to date are:

    1. Reducing the herd replacement rate by 1% for every 100 milkers results in a savings of 1.5 t CO2e/annum.  For example, if you milked 300 cows and reduced the replacement rate from 25 to 20%, this would equate to a savings of 22.5 t CO2e/annum.

    2. Reducing electricity consumption by 1000 kWh would save between 1.0 and 1.4 t CO2e/annum (range dependant on source of electricity with brown coal from Victoria the greatest emission factor).  For example, if your Victorian dairy farm used 75,000 kWh and you could reduce this by 10%, this would equate to a savings of 10.5 t CO2e/annum.

    3. Reducing nitrogen fertiliser inputs by 1 t N per annum would save 6.1 t CO2e/annum.  For example, if you reduced your N fertiliser inputs by 2.5 t N/annum, this would equate to a savings of 15.3 t CO2e/annum.

    4. Reducing the non-productive time for cows by 3 weeks (one breeding cycle) would save 12.6 t CO2e for every 100 milkers. For example, if the average inter-calving interval was reduced from 55 to 52 weeks for a milking herd of 500 cows, this would equate to a savings of 63 t CO2e. 

    5. Increasing milk production per cow, while increasing total farm GHG emissions, will decrease the GHG emissions intensity of milk production.  For example, for a milking herd of 250 cows with a liveweight of 550kg consuming an annual average diet with a dry matter digestibility of 75% and crude protein of 18%, increasing milk production from 500 to 550 kg milksolids (MS) per cow/lactation, would increase milk production by 12,500 kg milksolids/annum. Total farm emissions would increase as a consequence of the additional milk production and by 31.6 t CO2e/annum. However, the additional milk production would dilute this additional GHG emissions, with the emissions intensity of milk production decreasing by 0.04 kg CO2e/kg MS. NOTE: It is important to take into consideration the process by which the cows increase milk production.  If it is through increased grain feeding to improve diet quality, an estimate of the GHG emissions associated with the production and delivery of that grain needs to be taken into consideration.

  • Methane emissions

    Courtesy of their rumen microbes, cows produce and release methane. The methane produced by fermentation in the rumen is largely belched and breathed out by the animal. As a ruminant-based industry, it’s a reality we cannot escape. However, as methane is a high energy source (see below table), this represents a significant loss of energy from the production system (8 to 10% of gross energy intake is lost as methane), some of which can and should be redirected back into production (Eckard 2011).

    Table: Typical ranges in methane emissions, energy lost as methane and effective annual grazing days lost from three classes of ruminants. Source: Eckard 2011.

    Eckard 2011

    Methane is 25 times more potent than carbon dioxide in its global warming potential. That potency combined with the fact that a dairy cow belches about 600 litres of methane each day, make the annual emissions of a cow similar to a family car in terms of its effect on global (Read more - The Age article). It is estimated that a quarter of anthropogenic, or human-caused, methane emissions are due to enteric (rumen) fermentation.

    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).

    The proportion of an animal’s intake that is converted into methane is dependent on both the amount of feed eaten and the characteristics of the animal and the feed.

    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. For example, if grain supplementation is increased then three 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. 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.

    Possible options for reducing methane on dairy farms include:

    • Herd-based strategies, such as reducing herd size, reducing the number of unproductive animals, animal breeding, and/or rumen manipulation

    • Feed-based strategies, such as maximise diet quality/digestibility, pasture breeding and diet (feeding fats, oils and tannins).

    See Practices to reduce emissions.

    Under current policy farmers are not accountable for the on-farm emissions (i.e. methane and nitrous oxide).

  • Nitrous oxide emissions

    Nitrous oxide (NO2) emissions on dairy farms can be up to 25% of total farm emissions but three distinctly different processes contribute to this total:

    • 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.

    • 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.

    • 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.

    Possible options for reducing nitrous oxide emissions on dairy farms include:

    • Herd and feeding strategies, such as feed conversion efficiency, nitrification inhibitors, diet and effluent management

    • Soil-based strategies, such as improved drainage/irrigation and fertiliser management.

    See Practices to reduce emissions.

    Using effluent to offset fertiliser use can result in significant savings. Each tonne of nitrogen fertiliser applied to pastures emits 1.9 t CO2e directly and 2.3 t CO2e indirectly. In addition, the manufacture of fertiliser (urea) emits 1.9 t CO2e. Therefore a 1-tonne reduction in the use of nitrogen fertiliser will reduce emissions by 6.1 t CO2e.

    Similarly, reducing P and K fertiliser use by 1 tonne would save 4.6 t CO2e and 0.3 t CO2e, respectively, due to the reduction in emissions from manufacturing.

    In an ‘average’ farm system (300 milkers, average quality diet, around 6000 litres per milker), reducing the time spent in the dairy and yard by 10% (with cows spending this time on pastures instead) would reduce emissions by around 10 t CO2e / annum.

    The extent to which financial incentives (via the Emissions Reductions Fund) offered to farmers to reduce greenhouse gas emissions may change the economics of any of these options remains to be determined.

  • Carbon cycle

    Carbon is the universe’s fourth most common element and is the fundamental building block of all life on earth. At the global level, carbon moves between the atmosphere, the soil, living organisms, oceans and lakes, and into/out of long term storages – some movements occur in hours, while some long term storages of carbon (e.g. coal) have been locked up for millions of years.

    The carbon cycle on a farm is quite straight forward – it is simply the balance between photosynthesis (the process by which plants draw in carbon dioxide [CO2] from the air to produce sugars and release oxygen) and respiration (the process by which all living things release and use the ‘energy’ in food, drawing in oxygen and releasing CO2 to the air – ie the opposite to photosynthesis).

    The vast majority of the CO2 drawn from the atmosphere and used in photosynthesis on a farm is released back into the atmosphere within the same year. Most pasture is eaten by livestock or soil organisms, and most crops are grown, harvested and consumed all within an annual cycle and therefore on average, they create no reportable emission benefits or liabilities for any carbon accounting scheme.

    There are two potential exceptions to this ‘annual rule’:

    1. Additions to the long term soil carbon store, and

    2. Carbon stored in woody material, especially trees.

    Another possibility is bio-char – where organic matter is heated to 350-600°C under limited oxygen to produce a charcoal like material. The converts easily-decomposable organic matter into a stable form of carbon that potentially has soil improvement and carbon sequestration benefits.

     CSIRO 2010

    Figure: The terrestrial carbon cycle. Components (coloured boxes) and fluxes (white boxes) inside the grey area correspond to the carbon cycle under native unmanaged conditions. Items located outside the grey box identify the additional components and fluxes that need to be considered in managed systems. (CSIRO 2010)

  • References

    PDCCF fact sheets


    Other references