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By Ruth Dawkins 29 July 2020 6 min read

Soil organic carbon is the key to rich, fertile soil and offers tantalising environmental opportunities.

So, what is soil carbon, and why is it so important?

It all starts with photosynthesis. Carbon is captured from the atmosphere by plants, which convert carbon dioxide into plant material. When plants die, or components senesce, carbon is added to the soil and although much goes back to the atmosphere the size of the soil carbon pool may be increased.

Soil organic carbon (SOC) is an important indicator of soil quality and agronomic sustainability. It influences the physical, chemical and biological properties of soil quality, leading to effects on nutrient and waste cycling, water holding capacity, and biodiversity. Building and maintaining organic matter helps ensure healthy and productive soil systems and has the added bonus of removing carbon dioxide from the atmosphere, storing it in the soil and reducing greenhouse gas emissions.

Australian soils, however, have lost soil carbon in many cases. Historical conversion of land with native vegetation to agriculture has typically reduced soil carbon stocks by between 20 and 60 per cent.

What role does carbon farming play in Australia’s agricultural sector?

Carbon farming describes the adoption of management principles that maximise carbon sequestration in vegetation and soils, while simultaneously reducing greenhouse gas emissions and improving the productivity and resilience of agricultural systems.

Soil carbon can be increased in one of three ways. These are:

  1. Increasing the input rate of carbon, which can be done by increasing plant growth or cover, or by importing carbon through adding compost or mulch
  2. Decreasing losses, which includes things like reduced stubble burning or minimal till practices
  3. Increasing the residence time of carbon in the soil carbon pool by changing the profile of organic matter added to soil in a form that decomposes more slowly, or in a way that is protected by the chemistry of the soil; things like increasing clay content in sandy soils.

In the last 50 years, most Australian farmers have shifted from conventional agricultural practices towards conservation agriculture, taking an approach that has reduced the rate of soil degradation and improved crop water-use and production. The shift to low tillage, now adopted widely across cropping areas, is the most widespread change. Practices such as green manuring and leaving surface stubble are also steps in the right direction.

When bolder management changes are made – such as land use change, rotational grazing, and replanting native vegetation – even higher rates of SOC accumulation are possible.

One farm's trash should be every farm's treasure. Manure helps to fix soil organic carbon.

What are some of the challenges?

While there is potential for SOC to play a role in Australia’s emissions reduction efforts, the work involved in understanding and measuring soil carbon - including how it is impacted by different management practices and through time - has restricted widespread adoption of carbon farming.

Studies over a number of years have shown that SOC varies not just nationally or regionally, but often from paddock to paddock on the same farm. As a result, developing consistent accounting metrics for soil carbon remains an ongoing challenge.

Additionally, the diversity of Australia’s soils and agricultural systems means that even with good baseline data there is no one-size-fits-all solution to increasing SOC. The broad range of land use results in carbon farming opportunities that are not created equally across the country. Any management options for sequestering carbon in soils will have to be highly location specific.

Extensive work has taken place to build the underlying digital infrastructure that can support national assessments and help us progress to a carbon market approach supported by modelling. There has been significant research undertaken by CSIRO and others, including in the nationally coordinated Soil Carbon Research Program (SCaRP), to map Australia’s SOC levels and determine how these are related to environmental conditions, soil properties and agricultural management. This is included as part of a suite of maps in the Soil and Landscape Grid of Australia.

A key issue is that SOC is difficult to measure, making it difficult to produce the verification needed for carbon markets. New advances in soil sensing with instruments like CSIRO’s SCANS technology that rapidly scan the spectral signature of soil cores has the potential to rapidly drive down these costs.

Realising the opportunities

While we continue to make advances in understanding and measuring soil carbon, ultimately it is farmers who need to know that building soil carbon is good for their farms and their businesses. CSIRO has been exploring how information can be made accessible to farmers to aid their decision-making processes.

One recent example is LOOC-C, a free digital tool launched in late 2019 to help farmers identify what Emissions Reduction Fund (ERF) projects might be suitable for their land. With $2.55 billion available to purchase domestic carbon offsets, the ERF aims to incentivise the reduction of emissions and an increase in sequestration activities.

According to Dr Cara Stitzlein, a postdoctoral fellow with CSIRO’s Digiscape platform who specialises in human-centred design methodologies, there is a high level of interest in the ERF across the agriculture sector, but for many small to medium sized farms the levels of uncertainty around risks and transactional costs are barriers to participation in the scheme. That is an issue that LOOC-C aims to address.

“Farmers can use the LOOC-C tool to evaluate the carbon farming options for their land,” says Dr Stitzlein. “The first step is to pinpoint their property on a map, then the tool uses that paddock location alongside user-provided land management information to provide a list of eligible carbon project types and estimates of carbon credits that a project may generate. Importantly, the tool also identifies potential co-benefits and disbenefits that a project may generate.”

Dr Stitzlein describes LOOC-C as a conversation starter rather than a finished product, but notes that feedback from farmers is that the tool is intuitive and easy to use. Future iterations of LOOC-C will integrate additional project types into the tool, broadening the suggestions that can be offered to farmers. The focus on creating a tool that is fit-for-purpose, that is one representative of opportunities within the ERF, will remain central to its development.

“It’s crucial that we keep listening to farmers about the barriers and the factors that come into play in their decision making,” says Dr Stitzlein. “The idea of carbon as an additional revenue stream is an appealing one, but it's perceived as a partial solution to what they really want in terms of long-term sustainability and resilience across the entire farm.

"A complete solution, that unlocks opportunities in emerging environmental markets, requires innovative applications of both the biophysical and social sciences. The disciplines have to work together and with the feedback of farmers. Our experiences developing LOOC-C are being used in the next set of projects within CSIRO.”

Farmers are already adopting low- or no-till farming systems, but more can be done to protect soil carbon.

What next?

The potential of soil carbon in carbon markets has been identified as a priority under the Australian Government’s recently announced Technology Investment Roadmap. On the back of the worst drought in living memory, and the pressing need for action on climate change, there is a groundswell of interest in soil carbon as a means to build resilience in farms, sustain our productivity and enable the agriculture sector to play its part in reducing Australia’s GHG emissions.

There is broad agreement that soil carbon is an area where we can meet these challenges simultaneously. It will require the convergence of on-farm action, enabling markets, and policies at state, national and international levels.

The cornerstone will always be deep understanding of soil and farm systems, cheap and accurate ways of tracking changes and linking these changes to on-farm practices and interventions, and tools and approaches that allow those managing the land to assess and explore the options available.

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