Reducing Farm Emissions

Cows produce and release methane courtesy of their rumen microbes. The methane produced by fermentation in the rumen is largely belched and breathed out by the animal. As a ruminant-based industry, this is something that is hard to avoid.

However, as methane is a high energy source (see Table 1), this represents a significant loss of energy from the production system, with 8% to 10% of gross energy intake lost as methane. Some of this energy can and should be redirected back into production (Eckard 2011).

Table 1: Typical ranges in methane emissions, energy lost as methane and effective annual grazing days lost from three classes of ruminants. Source: Eckard 2011.

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
• 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 maximising diet quality/digestibility, pasture breeding and diet (feeding fats, oils and tannins)

Under current Australian Government policy, farmers are not accountable for on-farm emissions.

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

• Indirect emissions which the farmer has little or no influence over. 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 nitrogen fertiliser. This is the smallest contributor to dairy farm NO2 emissions, often less than 20%. Because of the cost, farmers are already focused on minimising the losses from nitrogen fertiliser, 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 nitrogen fertilisers during production may be a viable option. If this strategy reduced NO2 emissions from fertiliser by 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 nitrogen 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 and irrigation and fertiliser management

Using effluent to offset fertiliser use can result in significant savings. Each tonne of nitrogen fertiliser applied to pastures emits 1.9 tonnes of CO2 equivalent directly and 2.3 tonnes of CO2 equivalent indirectly. In addition, the manufacture of fertiliser (urea) emits 1.9 tonnes of CO2 equivalent. Therefore a one-tonne reduction in the use of nitrogen fertiliser will reduce emissions by 6.1 tonnes of CO2 equivalent.

Similarly, reducing phosphorous and potassium fertiliser use by one tonne would save 4.6 tonnes of CO2 equivalent and 0.3 tonnes of CO2 equivalent, respectively, due to the reduction in emissions from manufacturing.

In an average farm system, reducing the time spent in the dairy and yard by 10%, with cows instead spending this time on pastures, would reduce emissions by around 10 tonnes of CO2 equivalent per 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.

Nitrogen fertiliser use is essential in most dairy systems but the low efficiency of its use means that more than 60% of nitrogen added to pasture systems is lost to the environment.

With nitrogen efficiency often below optimum in dairy systems, there are a number of practical ways farmers can better match their nitrogen fertiliser applications with pasture demand, other inputs and prevailing conditions, thereby reducing input costs.

Practical advice on soil and fertiliser management is available via the Fert$mart website.

Key points to consider in nitrogen management:

• Poor nitrogen fertiliser management increases greenhouse gas emissions and wastes money
• Strategic use of nitrogen – when plants will respond and when extra feed is needed – saves money, time and emissions
• Poor irrigation and soil management practices will lead to loss of nitrogen from the system, including some as nitrous oxide

Suggested practices for nutrient management:

• Use best practice nitrogen fertiliser management to reduce nitrogen loss and improve nitrogen use efficiency and therefore profitability of nitrogen use
• Avoid high rates of nitrogen fertiliser, especially when soils are warm and close to field capacity
• Use best practice soil and irrigation management practices to make the best use of water, reduce soil inundation and minimise loss of nitrogen from the soil
• Reduce grazing on wet soils when urine patches will be most likely to emit nitrous oxide
• Nitrification inhibitors on fertiliser, fed to cows, or applied to pastures as a spray can reduce soil nitrogen loss as nitrous oxide

Although effluent management comprises typically only 8% of total farm greenhouse gas emissions, managing effluent storage and re-use to minimise emissions can provide broader benefits for on-farm efficiency, profitability and the environment. By viewing effluent as a valuable source of nutrients rather than a waste product, there are opportunities to save money on fertiliser, improve soil fertility and condition and minimise the risk of water pollution, as well as reduce emissions.

Soil carbon sequestration is the process of transferring carbon from atmospheric carbon dioxide into plant material, some of which is added to the soil carbon store as dead plant material or animal waste.

Soil is a complex mixture of organic compounds at different stages of decomposition. Soil organic carbon is divided into different ‘pools’ that are classified according to their rate of decomposition, as shown in Figure 1 below.

The amount of carbon in the soil depends on:

• The climate and soil fertility: fertile soils in high-rainfall zones or under irrigation can support high levels of plant growth and therefore have the potential to return large amounts of organic matter to the soil. The proportion of organic matter returned to the soil that is used for respiration by soil organisms depends on the soil temperature (higher temperatures, more respiration) and soil water content. The climate and soil therefore set the upper limit for soil carbon sequestration.
• The agricultural production system: more carbon tends to build up under pastures than under crops.
• Management: When soils are ploughed or otherwise disturbed, soil carbon previously protected from microbial action is decomposed rapidly. Systems that encourage the addition of plant litter to the soil, such as stubble retention or lax grazing, have some potential to increase the soil organic matter pool and eventually the soil carbon content, but the rates of change are slow.

Soil carbon sequestration under pasture - 2018

Dairy farmers have no control over their climate, little effective control over their soil fertility (most dairy soils are already highly fertile) and have a production system based on grazed pastures. Management is therefore the only significant option if dairy farmers wish to increase soil carbon.

Key points:

• Well-managed dairy pastures are generally regarded to be close to their physical storage capacity, so significant permanent addition is unlikely
• Australian soils are relatively dry and warm, which significantly limits the ability to build carbon content in the soil
• Soil carbon can be increased by growing additional dry matter or, for already high-producing pastures, by allowing more pasture to decompose. Adding carbon such as biochar is also possible, but that would be a cost to dairy farmers
• Raising soil carbon in the top 10 centimetres of soil by 1% over five years would require adding more than 10 tonnes of dry matter per hectare to the soil above current levels, which is clearly impossible even for dairy pastures
• The potential price of carbon would need to be very high (over $200 per tonne) to deliver a better return as soil carbon compared to using it for feed in milk production
• Building soil carbon requires significant nutrient inputs, particularly nitrogen, phosphorous and sulphur. If these have to be applied to raise soil carbon, the fertiliser cost must be taken into account in any analysis
• Under certain climate conditions, soil carbon increases could lead to higher emissions of nitrous oxide – another powerful greenhouse gas. This could see greenhouse emissions from participating farms increase
• It is expensive to accurately measure soil carbon with current technology and if the farmer has to pay for this verification then cheaper methods would need to be developed
• Soil carbon can change significantly with changes in weather, soil moisture and land use. This raises the question of what the risk is for farmers claiming credits at one point in time if they are audited later under different climate/land use and have to repay
• The requirement to retain claimed carbon in soil for at least 100 years has implications for long-term land use options, the value of land and the passing of obligations across generations. For example, a shift from perennial pasture to annual cropping in response to other factors such as water availability, temperature and markets can reduce soil carbon and hence may lead to an obligation on farmers to re-purchase carbon permits for claimed carbon credits that are subsequently lost

The magnitude and rate of soil organic carbon decomposition and sequestration depends on a range of soil and environmental factors.

To boost organic carbon concentrations in soil, two main options are available:

• Reduce the decomposition
• Improve the rate of addition of organic materials

In theory, any management practice that increases pasture production should lead to increased soil carbon because of the associated increase in plant material and animal dung. Practices such as fertiliser application, improved rotational grazing, irrigation and improved pasture species all have the potential to increase pasture production and thus soil carbon, though the impacts can be small and slow. Application of dairy effluent and sludge to pasture will also provide additional carbon inputs to the system.

These activities are already best practice on most Australian dairy farms because of the impact increasing soil fertility and pasture production has on farm profit. Therefore, while some farmers may have the option of implementing these management practices, for most the opportunities to significantly boost soil carbon will be limited. Additionally, if they are already considered good or best practice, such sequestration does not meet the requirement for 'additionality'.

For dairy farmers who grow crops and make silage, minimum tillage systems will reduce the rate of soil carbon decline in cropping paddocks. However, minimum tillage is already best practice for most soil types.

Biochar is a charcoal-like material produced by the pyrolysis (heating to between 350 degrees Celsius to 600°C under limited oxygen) of organic matter. This converts easily-decomposable organic matter into a highly biologically and chemically stable form of carbon that potentially has both soil improvement and carbon sequestration benefits.

Biochar is the solid by-product resulting from bioenergy production (Figure 2). The pyrolysis conditions can be optimised for bioenergy or biochar production.

• The national average energy use was 48 kilowatt hours (kWh) per kilolitre (kL) of milk, with a range of 31 to 66kWh per kL milk.
• The type of dairy does not affect energy use except for automatic, small rotaries (less than 150 cows) and large walk-throughs ( more than 300 cows), which all have higher energy use compared to others with a similar herd size. However, there is a herd size impact on energy use. Dairies with larger herd sizes have lower energy use per kL milk.
• There is no regional impact per se except that there is a different mix of sizes of dairies captured by energy assessments in the regions.
• Annual energy costs per business were highly variable and ranged from $1,663 to $121,722.
• The three main energy cost components are hot water, milk cooling and milk harvesting. These components make up on average 81% of each business’s energy use. This is equivalent to 40kWh/kL of milk for most dairies and 6okWh/kL for automatic dairies.

The most commonly identified savings were associated with:

• Improved functioning of equipment for milk cooling, including function of the plate-cooler and the compressors on the vats and using cooler water sources
• Pre-heating hot water for hot water systems, using heat exchange units (where appropriate) and using correct water temperatures
• Installing VSDs on vacuum pumps