Mr Mathew Warnken – The Benefits of Building Soil Carbon

1 November 2018 Geoffrey Craggs, Research Analyst, Northern Australia and Landcare Research Programme Download PDF

Key Points

  • The presence and concentration of soil organic carbon directly reflects on the health and the productivity of agricultural soils.
  • Organic matter in soil, though a small component, is important for plant growth by providing structure, nutrients and water.
  • Globally, Australia occupies an important position in respect to measuring soil carbon and developing innovative methods to build and increase carbon in our agricultural systems.
  • In agricultural soils, programs of successive plantings or pasture cropping and partial soil cultivation are an effective way to increase biological activity, building on carbon levels in the soil.



Farmers and land managers across Australia are continuing to work to develop and enhance their knowledge and understanding of the importance of building and maintaining soil carbon in agriculture. Many are focusing their efforts towards developing cropping and systems of agriculture by closely managing where and when they plant. These strategies combine with introducing organic in soil amendments and developing mechanical operations that both protect and augment soil structure which, in turn, aids water infiltration and holding capacity as well as encouraging biological activity.



FDI – What is soil carbon, how is it formed and how does it make soil more productive?

Matthew Warnken – Soil carbon has such a wide variety of connotations, often depending on the context and participants to the discussion. Everything from the largest disruptor on the horizon for mainstream agriculture, to a mildly interesting analyte in soil tests. As a non-soil scientist, I find it useful to start with a conceptual model of soil as a mixture of three main elements (in addition to air and water):

  • minerals from weathered rock,
  • organic matter which is the remains of plants and animals, and
  • living organisms such as plant roots, earth worms, fungi, bacteria and algae.

This is not to suggest that soils are relatively homogenous. For example, there is large variability in soils and soil types, with mineral components changing the structure of soil depending on the percentages of clay, sand and silt; the amount of soil organic matter (SOM) present adds to this variability. Even though SOM is a relatively small component of soil, anywhere from 3-10 per cent (and lower in many parts of Australia), it plays an important role in healthy soil function to supply nutrients and water to support plant growth.  Importantly, the SOM level relates to the ‘sponginess’ of soil, in that it provides good water infiltration and moisture holding capacity in addition to good airflow.

Soil organic carbon (SOC) is a subset of SOM and it relates directly to productivity in agricultural soils. That relationship is a function of the organic carbon content in soil improving water holding capacity and nutrient availability, in addition to improving conditions for soil biological activity. The higher the level of SOC, the greater soil productivity.

Australia holds a unique global position regarding soil carbon as demonstrated by the following:

  • Measurement: Australia has the only measurement-based framework for soil carbon credits, under a Regulatory framework. The Australian Carbon Farming Initiative Act (2011), and associated rules and regulations, sets out the legislative framework for emissions avoidance and carbon sequestration projects to create Australian Carbon Credit Units. The Measurement of Soil Carbon Sequestration in Agricultural Systems method establishes a soil carbon sampling and measurement basis for soil carbon projects across all areas of agricultural production, including grazing, dryland cropping, horticulture and viticulture.
  • Mechanisms: There is an increasing pool of innovative Australian regenerative farmers showing how SOC can be built under agricultural systems, as detailed in a recent report Innovations for Regenerative Landscape Management. Examples are:
  • grazing to manage groundcover and carbon sequestration
  • the application of recycled organics
  • improving biological activity in the soil
  • pasture cropping through multi-species plantings, over-sown into pasture.
  • Market: The Emissions Reduction Fund (ERF) is the only government-backed market place for the long-term contracting and purchase of soil carbon credits. Soil carbon projects have successfully bid for Carbon Abatement Contracts worth approximately $200 million at ERF auctions. These contracts provide a funding model for farmers, developers and landholders to register projects and engage with soil sampling and measurement requirements to create carbon credits.

As a result of these three key factors, Australia accounts for approximately half of all measurement-based soil carbon projects in the world. The Australian projects total around 30 and can be found in the Clean Energy Regulator’s Emissions Reduction Fund Register. There remains however, a large workload to increase project uptake and realise the full potential of soil carbon in Australia and abroad.

A useful international perspective on the opportunities and challenges for soil carbon projects is available through Carbon Market Incentives to Conserve Restore and Enhance Soil Carbon.

FDI – What is the Soilkee Renovator and what is its role?

Matthew Warnken -The Soilkee Renovator was invented by Niels Olsen and was further developed on his farm in Hallora, Victoria. Soilkee works in pasture cropping to combine cultivation, mulching, aeration and mixed species seeding to improve grazing systems and effectively build soil carbon. It works through activating several virtuous cycles. The patented action of the machine’s ‘kees’ simultaneously mulches plant matter into the soil (green manuring), aerates the top soil, mechanically assists rainfall infiltration, and cultivates a linear seed bed, while disturbing only 17 per cent of the soil surface. The mixed seeding ‘salad bowl’ approach to planting provides livestock with balanced nutrition and additional feed diversity, in addition to nitrogen fixing from legumes. This improves soils and increases feed quality and quantity. An example would be to sow a mixture of winter crops into a pasture that is active in summer months to boost overall fodder growth across the year.

In the case of the Olsen farm, it is estimated that the additional fodder produced has increased over the last six years by 40 per cent, demonstrating the prime agricultural driver of using Soilkee. The added productivity becomes the main motivator for ongoing Soilkee use.

Each successive planting drives additional root biomass into the soil. After grazing, the root biomass from annual plants dies off and decays, continuously adding to the pool of SOM. This has the function of creating a virtual ‘carbon pump’, where compounding increases in SOM, acts as the foundation for continuing sequestration of SOC. The actual effect is a deepening profile of healthy soil with good worm activity, worm castings, bacteria and nodulation in nitrogen fixing legumes.

Soilkee agronomic benefits are well documented in the West Gippsland Catchment Management Authority soil pasture demonstration involving Soilkee, pasture aeration and a control site. Treatments carried out showed improved species of grasses with good response to rainfall and evidence of pasture quality through observed preferential grazing by livestock.

Correspondingly, clover was noticeably bigger, there was evidence of worm castings and the soil was observed to be spongier underfoot. Soil tests across the three treatment sites showed an increase in available nutrients, improved chemical processes such as cation exchange, and ratios in beneficial nutrients. Also evident were increases in dry matter yield in combination with coverage of perennial rye and clover.  These factors form the basis of visible evidence of improved agricultural productivity.

FDI – What benefits would farmers gain from what you are proposing?

Matthew Warnken – Improvements in soil carbon are driven and supported by improved agricultural management. Soilkee is one method that provides a programmed ‘treatment’ regime for farmers to follow. Benefits to farmers include:

  • Increased livestock feed – additional crops over sown onto pasture means more feed per hectare, therefore reducing the need to purchase additional feed from ‘off-farm’ sources.
  • Improved fertiliser efficiency – nitrogen fixing legumes planted as part of the ‘salad bowl’ approach means lower requirements for fertiliser inputs through the growth of nitrogen with combined with improved plant availability.
  • Improved water use – better water infiltration and holding capacity means better water efficiency and less waterlogging, in turn contributing to greater ‘on farm’ water carrying capacity.
  • Better quality soil – increasing SOM, improved water holding capacity and biological activity delivers improved plant nutrition which, in turn, delivers better animal nutrition and better performance per animal.
  • Soil carbon credits – measured increases in SOC can create carbon credits so that farmers can be paid to improve the health of their soils and overall farm performance.
  • Better farm management – implementing a soil carbon project provides farmers with a digital map of their underground resource. This soil map aligns with world leading practice, providing farmers with better data to inform better agricultural decisions, resulting in increases in farm performance.
  • Risk management – the combination of the above benefits provides an effective risk management strategy for farmers through building resilience and increasing drought tolerance.

An additional benefit for any farming system operating under a quality certification program, such as ‘organic’ or ‘biodynamic’, is that growing additional feed ‘on-farm’ lowers associated costs with purchase of feed from ‘off-farm’ sources.

FDI – What role does your organisation Corporate Carbon play in this process?

Matthew Warnken – I founded Corporate Carbon in 2010 to provide solutions that would enable the creation of carbon credits from emission’s avoidance and carbon sequestration projects. Since then, we have been involved in over 100 projects and have grown to be the largest multi-sector project developer and aggregator in Australia. Soil carbon is a key strategic focus for us, especially because there are no land use tradeoffs.  Every carbon credit issued to a soil carbon project is, in effect, a measurement of increased productive capacity and evidence of a regenerating land system.

The work we started in soil carbon is being further developed through a special purpose company ‘AgriProve’ that will build on the soil carbon project at Niels Olsen’s farm. This project was registered under the Australian Government’s ERF and is the first project to go through audit which confirmed a measured soil carbon increase of 11.2 tonnes of carbon dioxide equivalent per hectare over a 12-month period. We are finalising the accompanying administrative requirements and aim to make an application for the first soil carbon credits in Australia. This is notable because it would signify the world’s first issuance of soil carbon credits, under a measurement regime and within a Government-regulated program.

Following that ‘lighthouse project’ AgriProve is developing additional Soilkee carbon projects throughout Victoria’s Gippsland area and in other suitable regions around Australia.


About the Interviewee:

Matthew Warnken is founder and Managing Director of Corporate Carbon, Australia’s leading cross-sector developer and aggregator of carbon abatement projects under the Emissions Reduction Fund.  Matthew has formal training in natural resource management, engineering research and business. He is leading the commercialisation of soil carbon projects in Australia through ‘AgriProve’, a start-up agri-tech business.

Any opinions or views expressed in this paper are those of the individual author, unless stated to be those of Future Directions International.

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