An awareness of climate change and associated issues has raised expectations of some farmers of the possibility that measurable increases in soil carbon levels producing a cash value in the future should carbon-trading ventures begin.

Soil carbon levels have long been recognised as an indicator of soil health due to its capability to influence soil physical, chemical and biological properties and so are a reflection of what we do right in our farming systems. With approximately 76% of Australian soils having less than 1% organic carbon, there should be the ability to increase this level, right?....Well, maybe…as it also depends on the type of organic matter.

Work conducted by CSIRO scientists Jeff Baldock and Jan Skjemstad have shown that there are two distinct carbon pools in the soil – a biologically stable pool of old carbon (dominated by microscopic charcoal fragments) and an ‘active’ carbon pool that is cycled through biological systems in the soil and by crops.

The stable pool is very difficult to add to and can account for 60% of the organic carbon present in Australian soils.

The remaining 40% of the organic carbon pool we are able to influence through farm management. However, in low rainfall environments this is difficult due to crop production being limited due to season and therefore the amount of residues returned to the soil is highly variable.

Soil type is another influencing factor with clay soils being better able to “protect” carbon than the predominantly sandy soils of Central and Upper Eyre Peninsula.

As you can see, in farming systems carbon sequestration is difficult to measure due to the variability of biological processes and systems.

Whilst aiming for increasing soil carbon levels is still a valid and valuable goal due to the long recognised benefits of increasing water holding capacity, positively influencing the exchange and buffering capacity of the soil, increasing aggregation and aggregate stability and increasing absorption and infiltration, any financial benefits that farmers might realise might be limited (for now).

AUTHOR: Liz Guerin, Soils and Land Management Consultant, Rural Solutions SA
CONTACT:   Liz Guerin, Soil and Land Management Consultant, Rural Solutions SA  Streaky Bay, telephone 08 8626 108 or, mobile  0427 261 671.