Australian farmers can play an important role in mitigating climate change - and the good news is that actions that reduce greenhouse gas emissions usually also have productivity benefits on-farm. Planting trees helps increase carbon storage while also providing shelter for stock; more efficient use of inputs such as nitrogen and so on. Here we outline the relevant green house gases to agriculture then look more closely at what can be done on-farm.

But first, what is mitigation? Also referred to as abatement, mitigation refers to any action that keeps greenhouse gas emissions from going into the air and adding to global warming, usually measured in tonnes of carbon dioxide equivalents, CO2-e or just the shorthand ‘carbon’. It includes stopping emissions at their source—such as reducing fossil-fuel dependence and deforestation—as well as drawing carbon down out of the air and storing (or sequestering) it in trees and soils. For agriculture, there are three key greenhouse gases: carbon dioxide, methane and nitrous oxide.

What are greenhouse gases?

Carbon dioxide (CO2

Carbon dioxide is the greenhouse gas driving most of the global warming seen since the Industrial Revolution started in the 18th century. Today, the big, global sources of CO2 are the combustion of coal, oil and gas, as well as deforestation and soil degradation. There are also sinks of carbon, principally vegetation, soils and the world’s oceans, which dissolved CO2 is making more acidic. In 2018, carbon emissions hit an all-time high of just over 37 billion tonnes and CO2 levels are now about 45 per cent higher than they were in pre-industrial times.

In agriculture, CO2 is produced when bushland and other vegetation is cleared, burned and decays. Of course, plants need CO2 to respire and grow, so growing trees, pasture and crops absorb carbon via photosynthesis. Carbon from organic residues (e.g. dead leaves, roots, manure and urine) is also incorporated into soil. Unless sequestered, CO2 lasts for centuries in the air, where it continues to warm our world.  

Methane (CH4)

Atmospheric methane stems from a mix of natural and unnatural sources, such as coalmines, gas wells and leaky pipes, burning and rotting vegetation, landfill, and ruminant livestock (burps and dung, including wastewater ponds in dairies and piggeries), and rice paddies. Methane-producing (methanogenic) bacteria in their forestomachs allow cattle, sheep and other ruminants to digest and extract energy from otherwise indigestible plant matter.

The global warming potential of CH4 is approximately 25 times that of carbon dioxide over a 100-year period, and more in a shorter time. Methane, however, lasts for only about a decade in the air, broken down mainly by sunlight and atmospheric chemistry. Importantly, though, while the warming effect of any given emission of methane is temporary, the total warming impacts will continue for as long as the source of methane continues. Since the start of the Industrial Revolution, methane concentrations in the atmosphere have risen by around 150 per cent. Some of this additional methane is from fossil fuels, some from deforestation, and some from expanding agriculture—mainly livestock, which now far outnumber wild ruminants. 

Nitrous oxide (N20)

Nitrous oxide is a very potent greenhouse gas, with a global warming potential more than 300 times that of carbon dioxide in a given century. Nitrous oxide is also emitted when soils are disturbed, through erosion and leaching into waterways and the air, from the application of nitrogenous fertilisers (e.g. urea), and from livestock urine and dung. Legumes use nitrogen-fixing bacteria to draw nitrogen down out of the air and turn it into compounds vital to other plants. 

For farmers, wasted nitrogen is wasted money. Improving nitrogen-use efficiency makes sense financially as well as environmentally. Unfortunately, what is an optimal N input (fertilisers and legumes) for pasture isn’t for livestock, with most of the nitrogen consumed by ruminants excreted in urine and dung—two of the largest sources of nitrous oxide emissions from grazing properties. 

What can be done on-farm?

There are a number of options open to farmers looking to mitigate greenhouse gas emissions on-farm. Below we profile just a few.

Get a handle on the farm’s carbon balance

A number of tools and guides exist to help producers understand their carbon accounts, i.e. the sinks and sources of carbon emissions. A tool should be fit for purpose and scientifically sound. If you’re just starting out you may want something relatively simple that gives you a rough idea of where you can make changes. Entering the carbon market, however, or making claims to consumers will require more rigorous accounting.

Some tools to get you started:

For more on carbon accounting see our carbon storage page.

Reducing emissions from livestock

Livestock emit methane and, to a lesser extent, nitrous oxide. One way to look at methane, in particular, is as wasted energy—up to 10 per cent—that might be better used to grow healthier animals, producing more meat or milk. Recently, there have been some very promising developments in quest for better productivity and sustainable livestock systems. For instance, studies of dairy cattle fed red algae—which change the mix of bacteria in the rumen—show very impressive drops in methane emissions. Also under development are vaccines that inhibit methane-producing bacteria. 

Meanwhile, a range of low-emissions livestock strategies is available right now. Often, these deliver productivity, animal health, and adaptation benefits. More and more producers are starting to reduce the emissions intensity of their livestock, i.e. less methane per unit of meat or milk. This is an important strategy but only if productivity dividends are not then used to expand the herd and raise emissions overall. 

Techniques and strategies to reduce emissions from livestock include:

  • Managing pasture quality (e.g. maturity, legume content, etc.) through grazing strategies, such as rotational grazing, to optimise feed value. 
  • Growing a variety of high-quality forage crops, and/or supplement grazing stock’s diet with grain or other energy-rich, low-fibre feed (e.g. during summer and autumn). The better the quality of forage (pasture, hay or grain) the more energy the animal’s rumen bacteria can extract from it and the less methane is produced. 
  • Finishing stock in feedlots reduces the time to market, hence reducing emissions intensity. 
  • Minimising nutrient excretion to reduce N2O emissions. As far as possible, match the protein-to-energy ratio of livestock feed with animal requirements. Young, growing stock and lactating females have a higher need for protein than dry stock. Feed demand calculators are now available to help.
  • Focusing on animal health, genetics and reproductive efficiency. A healthy animal is not only more valuable, it also tends to have a lower emissions profile: 
    • Minimise heat stress in your animals, providing adequate water and shade. 
    • Maximise the proportion of young, growing or lactating stock.
    • Optimise fertility through good health and body condition.
    • Minimise the loss of newborns through good husbandry, including adequate shelter. 
  • Breeding for a smaller but high-performance herd or flock. Select animals for productivity traits such as growth rate, fecundity, feed-conversion efficiency, and disease resistance. Identify, monitor and cull less productive stock. 
  • Supplementing animals’ diet with tannin-rich plants (e.g. legumes), Leucaena, lucerne, vetch, lotus, and native shrubs such as Eremophila, as well as linseed oil and grape marc. All of these are known to significantly reduce emissions. 

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Nutrient management

Australian agricultural systems typically apply more nitrogen than they need, wasting resources and money, and risking contaminating the environment. There are several ways to save nutrients and reduce emissions, with little to no negative impact on productivity:

  • Careful timing and measuring of nitrogen fertiliser inputs to match crop/pasture needs can reduce losses—by as much as 80 per cent in some systems.  
  • Nitrification inhibitors can help to moderate the conversion of N fertiliser. Note that not all inhibitors are suitable for all farming systems so it’s wise to monitor performance. 
  • In rain-fed farming, farmers can raise nitrogen (and carbon) stores in the soil by cropping less frequently and making more use of legumes and/or pastures. Depending on the farming system, adding legumes can reduce the need for synthetic nitrogen by half to near zero without reducing yield. 
  • To reduce N2O emissions from irrigated agriculture, managers should reduce either run-off or nitrogen load in the water, or both. 
  • Consider using slow-release N fertilisers based on modified biochar (activated charcoal) where available
  • Avoid soil compaction, pasture plugging, and other activities that cause soils to become poorly aerated and promote nitrous oxide emissions. 
  • Careful management of livestock effluent can significantly reduce nitrous oxide emissions. This includes covering stockpiles and managing manure piles to avoid anaerobic conditions. Limiting effluent storage in ponds and covering manure stockpiles has been shown to cut methane emissions by as much as 88 per cent. Consider regularly de-watering storage ponds (every six months or so) and anaerobic ponds (every three years) by irrigating crops and pastures, fine-tuning the timing according to your rainfall. Sorbers (insoluble material used to recover water) can improve crop yield while reducing N2O and ammonia emissions.
  • If using slurries or manure as fertilisers, measure the nitrogen content before application for more efficient use, and avoid applying when the soil is wet. Composting or pelletising animal manures will also significantly reduce emissions.  
  • Incorporating animal manure into soil will help to reduce nitrous oxide and methane emissions emissions, as well as improve soil structure, often without reducing productivity. In some but not all cases, the action of livestock hooves can help. 
  • Minimising nutrient excretion to reduce nitrous oxide emissions. As far as possible, match the protein-to-energy ratio of livestock feed with animal requirements.

Keep reading: