Key Factor #2: Myths About Australian Soil C

The science of soil carbon has been misinterpreted in Australia, so much so that “myths” have gained traction in the public mind.

The dominant view of the soil C sequestration potential of Australian soils in the scientific community, among policymakers and industry opinion leaders was established at a 2000 workshop sponsored by the CRC on Greenhouse Accounting on sequestration. The report concluded that:

“Australian climate, soils and agricultural management histories are significantly different to those of developed countries in the northern hemisphere. These differences generally result in considerably less potential for increase in soil carbon stocks associated with changing crop or pasture management practices in Australia compared with northern temperate regions.” (8)

While this was not a definitive statement, the conclusion was distilled in an Australian Greenhouse Office policy framework document as: “Typically Australian soils have a poor capacity to store large quantities of carbon." (9)

This statement was based on research done for the National Carbon Accounting System (NCAS). But analysis of Technical Reports 34 and 43 (10), the core data reports for the construction of the NCAS, reveals that the data sets are incomplete, focusing almost exclusively on conventional rather than regenerative land management techniques. It studied only soils managed in ways that caused losses of carbon rather than samples managed in ways that capture and store carbon (ie. regenerative land management techniques such as biological farming, time controlled grazing management, pasture cropping, etc.)

For this reason, there are gaps in the data sets.

Therefore the data cannot support the conclusions being drawn from it.

The authors of the Technical Report 34 complained that the study was insufficiently resourced to cover the range of land management styles:

• “As it would have been too time-consuming and expensive to examine land clearing in all parts of the State, the AGO specified that this project should focus on certain clearing hotspots in NSW…” (Ie. only high emissions locations were selected.)

• “However, with resources for ten possible comparative sites, only a limited range of land-use transitions were included in the study… It should be noted that ten paired sites is not a sufficient number to adequately sample all the land use changes that are occurring in the clearing belt in NSW… (Ie. insufficient data sets.)

• “Classifying the paddock histories into particular management practices can be difficult, as a ‘recognised practice’ may have considerable variation in the methods and effectiveness with which it is implemented. The environmental and economic conditions under which practices are implemented can also vary. Both these things can cause variability in any expected changes in soil properties...”

The authors of Technical Report 43 also complained of a lack of data (11):

“Data from over 50 independent studies across Australia was compiled to create a comprehensive data set of 586 values. Information identifying associated site histories, climate and soil type was recorded.

“Of the trials considered, many had incomplete information, lacking details on:

• soil properties below a depth of 10 cm;
• carbon densities;
• soil bulk densities;
• implements used during tillage operations;
• other issues relating to tillage operations;
• stubble management practices; and
• historical site management data.”

The consultant hired to assess the data sources was also concerned: “While there are some very useful datasets available, there are also considerable deficiencies in the completeness of the data… In many established agricultural areas, there are practical difficulties in finding true pairs… The approach is limited by gross lack of data…” (12)

Data issues also plagued the Roth C Modelling system, developed to model the effects of agricultural management on the stock of organic carbon, which may have skewed results:

“There are difficulties associated with collecting pasture residue data…There are deficiencies in knowledge of carbon dynamics in these situations and the capability to model residues in soil are relatively undeveloped. Uncertainties in soil carbon dynamics through factors such as grazing pressure, pasture production responses, excreta inputs and carbon immobilisation, restrict confidence in modelling of soil carbon inputs. The option for these areas is to use models to estimate average residue inputs under grazing, acknowledging the constraints to the data, and to use a panel of experts in each grazing region to review the estimates.” (13)

The data was insufficient. “Development of the NCAS was undertaken with the clear understanding that data would be imperfect, but that the significance of data limitations could be assessed only in a functional integrated system.” (14)

The AGO took a ‘fix it in the mix’ approach: “The tacit acceptance of variability in data provided for a proper focus on matters of accuracy and bias, rather than on potentially unachievable precision.” The Agency believed the sheer weight of data points would carry the day, provided there was no bias in the inputs: “Over a large sample … a national inventory derived from an aggregation of fine-scale events can provide a robust central estimate provided inputs are not biased.”

But the inputs were biased. The data sets were incomplete.

Despite this obvious defect in logic or basic scientific methodological process, the potential of Australian soils was dismissed as a Climate Change mitigation solution. And this myth grew in the telling. Our soils were not only too degraded to sequester carbon, they were also too old. (NB. Neither of these factors affects carbon sequestration.)

The Australian Farm Institute added its gravitas to the myth: "The bulk of Australian farms may not operate as carbon sinks, due to the age of the soils." (15)

The most definitive version of the myth was announced by the Grains Council: “Given the age and degraded nature of Australian cropping soils and the ‘natural’ low levels of organic carbon, there is no scientific evidence to suggest that there is a real possibility that organic carbon levels can be increased by cropping or farming practices at anything other than slow rates, reaching an equilibrium point well below that of northern hemisphere soils.” (16)

The head of the soil science department at a leading university – on hearing of this comment - laughed out loud: "What a curious thing to say. Soil age is irrelevant.” A senior government soil scientist working in the field said: "There are many myths out there. The people who make these remarks don't get around enough to know what's going on."

The Grains Council took to the airwaves in an energetic campaign to bury Australian soils: “Our soils are very old, very fragile, very thin, very weathered. Often we are running soils with 1% or less carbon.” (17)

Generalisations about Australians soils are dangerous. Alpine soils can contain around 10% soil carbon, and desert soils around 0.5%. Soils tested for soils workshops with farmers at Mudgee and Rylstone have between 0.9% and 7% Carbon and averaging 2.2% at Mudgee and 2.7% at Rylstone. (18)

One percent of carbon is a significant amount. It can translate into 42 tonnes of soil carbon which equates to 154 tonnes of CO2e per hectare (at Bulk Density 1.2 and 30cms depth). A 1% increase in soil carbon per hectare – at $25/tonne – in this situation would be worth $3850. Multiply by a thousand hectares and you have a significant figure.

The Grains Council was broad ranging in its arraignment of Australian soils: “The limited potential for Australian soils to increase levels of organic carbon, with estimates by many scientists of less than 100kg per hectare per year, even under the most effective non irrigated farming systems.”

No AGO research has studied the “potential” of Australian soils to take up carbon. Most official studies recorded poor carbon performance because they studied only traditional techniques which are destructive of soil carbon. They did not find sequestration because they weren’t looking for it.

They were looking for declining carbon. The paradigm under which the NCAS was constructed was of an Australia forested from shore to shore when Captain Cook arrived. The arrival of Europeans was disastrous for native vegetation. Australian agriculture was, by nature, destructive. Deforestration was the key activity and it was assumed it always led to soil C depletion.

“This project [the NCAS] emanated from the need to consider the temporal and quantum extent of change in soil carbon, due to land use change that involves the clearing of forest and woodland.” (19)

There are several trials underway to fill the gaps. Further evidence that the gaps existed and the conclusions were unsustainable.

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FOOTNOTES:

(8) Keenan, R., Bugg, A.L., Ainslie, H. (eds) (2000) Management Options for Carbon Sequestration in Forest, Agricultural and Rangeland Ecosystems. Cooperative Research Centre for Greenhouse Accounting, p. 1

(9) Australian Greenhouse Office, Developing a Strategic Framework for Greenhouse and Agriculture. An Issues Paper, 2002

(10) Technical Report No. 34 Paired Site Sampling for Soil Carbon Estimation – NSW, National Carbon Accounting System, Australian Greenhouse Office, January 2003

(11) “The Impact of Tillage On Changes in Soil carbon Density with Special Emphasis on Australian Conditions”, National Carbon Accounting System Technical Report No. 43, Australian Greenhouse Office, January 2005 (See Appendix 1)

(12) Estimation of Changes in Soil Carbon due to Changed Land Use
National Carbon Accounting System - Technical Report No. 2 November 1999

(13) Technical Report No. 2

(14) “Methods for Estimating Land Use Change Emissions “, Factsheet, National Carbon Accounting System, Australian Greenhouse Office, August 2002
(15) Mick Keogh,
(16) “Carbon in Australian Cropping Soils: A background paper prepared by Alan Umbers For the Grains Council of Australia.” July 10th 2007
(17) Alan Umbers, Grains Council, ABC Radio Country Hour, 11 July, 2007
(18) Private conversation, Soils Coordinator, Central West Catchment Management Authority, July 2006
(19) Technical Report No. 2