A soil carbon troppo dream

As outlined in the government’s Direct Action Emission Reduction Fund Green Paper, it faces a major challenge. The government needs to find 431 million tonnes of CO2 abatement to reach its 5 per cent reduction target, but only has maybe $10 to spend per tonne, based on what little detail we have available on its funding.

So far, energy efficiency is the only credible large scale cheap (<$10/tCO2) abatement measure identified; the previous Greenhouse Friendly and NSW NGGAS schemes included such measures but failed to create anywhere near the amounts of abatement required by Direct Action.

That leaves ‘soil magic’ – simply putting carbon cheaply into soil to account for up to 65 per cent of planned emissions reductions (as originally stated in the Liberals’ climate policy, now removed from their website). No reputable soil scientists from the CSIRO or the universities say this is achievable, and I explained how this idea has no chance of being achieved even if 2-10 times the money allocated were thrown at it. 

But the Coalition is evidently unfazed by the lack of scientific evidence, and seems more concerned with creating impressive visions. Late last year a defence-oriented think-tank produced a ‘conceptual paper’ which cites no author or references and appears to advocate ‘soil magic’. Future Directions International is chaired by former governor-general and military hero Michael Jeffery; it includes several distinguished military and business luminaries on its board and over a dozen professors as associates. The paper is entitled Regenerate Australia, Our Greatest Challenge and Opportunity.

Having worked for 15 years in land and soil management, I was pleased to be asked to have a look at it. But it soon became evident that the anonymous author has no knowledge of rangelands, tropical agriculture, soil carbon or carbon emissions and has not listened to anyone who has. 

The paper proposes "introducing sufficient grazing to reduce vegetation" by "digging 200,000 earth tanks across the wet tropics" and has the grand aims of "managing additional grain production to feed up to one billion people" and running "up to 100 million cattle" (about four times the existing national herd).

What is truly dismaying is the paper’s linking of this grand strategy to carbon abatement: “Over time, this could double ...  carbon fixation ... of Australia’s 'green deserts'". These bio-systems should be able to fix 5-10 tonnes of carbon per hectare per annum, resulting in the possible sequestration of over 1500 million tonnes of carbon per year, or 10 times Australia’s current annual industrial carbon”.

There are many false statements and omissions in the paper. Firstly, the best possible soil carbon uptake is by irrigated crops and pastures (up to 2 tonnes CO2 per hectare) and perennial pastures on country with high water tables (up to 1.6t – see this study for further detail). The author’s claim of 5 tonnes of carbon, which equates to 18 tonnes of CO2, is preposterous and irresponsible, even if he were talking about the world’s most productive irrigated soils. That he claims it for over 300 million hectares of wet tropics, most of which is ‘hard country’ with poor soils and no significant potential to harvest fresh surface or ground water for irrigation, is crazy ‘kite flying’.

Secondly, it omitted the fact that 100 million cattle emit about 100 million tonnes CO2 equivalent of methane from ruminant digestion.

Thirdly, intensive rangeland grazing invariably causes soil erosion and loss of carbon in times of drought, which occurs at least annually through the 10 month ‘dry’ period of the tropical north.

Another unfounded premise of the paper is that the carbon emitted by rangeland burning could be prevented and instead fixed in the soil. This is partly possible but not economically feasible. If the ‘cane grasses’ that occur naturally on the minor percentages of better soil could be cultivated or mulched in when green and not grazed or cropped, some of the carbon, maybe up to 2 tonnes CO2 per hectare, could be sequestered in the soil. But what would be the cost of cultivation by heavy machinery with no agricultural production? I estimate about $200 per hectare or more than $100 per tonne CO2; a pointless exercise that would have to be continued indefinitely to prevent release of carbon back into the atmosphere by erosion and oxidation.

Let's be optimistic and say that the Ord River Scheme could be expanded several-fold to produce irrigated crops from up to 100,000ha, or 0.003 per cent of the 300 million hectares of wet tropics cited in the paper. It may even provide up to 200,000 tonnes of CO2 abatement per year in soils, or 0.02 per cent of the 85 million tonnes the Coalition needs. The Ord is of great social and strategic importance, enabling a town, tourism, and agriculture to be built in a previously uninhabited area. Other areas suitable for irrigation should be identified and costed; more schemes like the Ord would be great for the nation. Even better if they could be made economic, but this has not been achieved despite 45 year years of intensive work and investment in the Ord. It will take a lot more than a few million dollars in carbon credits to achieve that.

This is not to say that land management in the wet tropics cannot deliver some carbon abatement. The greenhouse gas nitrous oxide is emitted during ‘hot’ savannah burns. Indigenous communities are already creating carbon abatement by conducting ‘cool burns’ in the cooler months, but this has nothing to do with increasing cattle grazing or irrigating vast tracts of land.

Papers such as this by the FDI do nothing towards cheap carbon abatement. Major-General Jeffery, his board of directors and professorial associates would be well advised to ensure that all of their papers are peer reviewed, with references by experts. One hopes that the Coalition is not linked in any way to this paper, as it would only cause embarrassment and loss of credibility to both parties.

Ben Rose is a Western Australian land management scientist who has consulted in carbon sequestration analysis. He worked for a year in tropical agriculture on the Ord River, five years in rangeland management and 10 years in soil conservation.