Menu lock


Feb 4, 2010

Soil carbon: big potential, but maybe not yet?

The Coalition is relying heavily on soil carbon to provide emissions reductions under its new climate change plan. Not so fast, say experts.

One of Australia’s foremost soil carbon experts has significant concerns about the Coalition’s proposed funding of soil carbon initiatives, on which the Coalition is relying for more than 60% of its emissions abatement task between now and 2020.

Professor Alex McBratney, Pro-Dean of Sydney University’s Faculty of Agriculture Food & Natural Resources, has told Crikey that the $8-10 cost per tonne of CO2-equivalent on which the Coalition has based its figures is probably too low given the cost associated with sequestering soil carbon.  “It needs to be closer to $20-40 a tonne to be viable.”

Professor McBratney’s comments follow eminent scientist Peter Cosier’s criticism that farmers would be receiving more under the Government’s CPRS than under the Coalition’s plan.

However, Professor McBratney is very optimistic about the potential for sequestering soil carbon and believes the Coalition is being conservative on its long-term potential.

Soil carbon — increasing carbon levels in soil through no-till or lower-till cultivation methods, composting or adding biochar to soil —  has huge potential for biosequestration of carbon, locking carbon in soil for decades and, possibly, hundreds and thousands of years.  It has some heavyweight backers. James Lovelock, James Hansen, Tim Flannery and Ross Garnaut are just some of climate change icons that urged a serious effort on biosequestration.  Malcolm Turnbull began promoting soil carbon and particularly biochar early last year, and proposed that farmers be permitted to obtain credits under the CPRS for it on  an opt-in basis.  The Government later agreed to that and it now forms part of the revised, Turnbull-era CPRS Bill reintroduced into Parliament on Tuesday.

However, soil carbon has come under attack from left-wing environmental groups, who argue that its biosequestration potential is as yet unproven and that demand for products such as  biochar will see biosequestration competing with food production as biofuels have, leading to higher food prices.

Critics say there is insufficient peer-reviewed evidence of the long-term stability of soil carbon, and that there is some evidence that no-till and biochar use actually reduce soil carbon levels.  No-till cultivation also requires greater use of herbicides (and has been encouraged by agri-multinationals such as  Monsanto for the reason), or organic farming methods, which mean significantly more expensive food.

Biochar has come under greater scrutiny.  It is produced from biomass such as agricultural waste through a heating process that can also produce biofuels.  Very fine black carbon is susceptible to blowing or draining away — one Canadian study showed 25% loss in the process of transporting and spreading, including photos of clouds of black carbon — a particularly intensive greenhouse contributor — blowing away during spreading.  In many cases, composting the original waste material rather than turning it into biochar is more viable.  It is the production of biochar that critics believe has the potential to drive up food prices.

Soil carbon credits also have no value under current international carbon trading rules, although as Tony Abbott has noted, that’s a secondary issue if soil carbon delivers a genuine carbon sink — it removes CO2 from the atmosphere.

But while objections to biosequestration seem mainly confined to the hairshirt elements of the environmental movement, there is broader agreement that accurate measurement of soil carbon needs to be resolved before it can be viable.  The CSIRO last year started a multi-year project to address issues in soil carbon measurement and said yesterday much more research needed to be done.

Professor McBratney who has undertaken extensive work on the issue, believes these issues will take 2-3 years to resolve but says relatively accurate measurement of soil carbon levels can be obtained at reasonable cost and form the basis for paying farmers.  However, he proposes some caveats — a payments system should be based on whole units — such as an entire farm — so that total net carbon loss or gain can be monitored, and it should include all carbon — he says soils also contain non-organic carbonate carbon, which can be lost through irrigation and therefore any system must be on a “net carbon” basis.

He also suggests payment systems be based on relatively conservative verification systems, and if farmers want to be paid more, they pay for more accurate testing.  Soil carbon credits are available on the Chicago Climate Exchange, he says, but are worth less than $US1 due to the lack of independent verification and reliance on estimation rather than measurement.

Professor McBratney also proposed farmers be paid an ongoing, rather than one-off, payment as an incentive to maintain soil carbon levels.

He would prefer to see a market-based mechanism, and believes $8-10 “won’t cut it”.  “Increasing soil carbon levels requires greater production levels or addition of biomass.  Adding a tonne of carbon to soil requires about 100 kilograms of nitrogen, and that either has to be purchased  at about $1 per kilogram or produced via legumes, which need water.”  Professor McBratney thinks $20-40 a tonne is a more realistic but still conservative cost.

However, he says there is enormous potential for soil carbon sequestration and that Australia is probably the world leader with the most sophisticated public debate in the area.  “You’re not going to see anything for the next two or three years but by 2020, we should start to see a real difference. A reasonable aspiration is a 20% increase in soil carbon by 2020.”

That assumes our politicians managed to get the right incentives in place.

We recommend

From around the web

Powered by Taboola


Leave a comment

8 thoughts on “Soil carbon: big potential, but maybe not yet?

  1. Greg Angelo

    Soil carbon sequestration appears substantially to be pea and thimble trick with only the potential for short-term gain. One assumes that with low till farming organic matter would presumably remain the soil for some period with a consequential lower rate of oxidisation returning the carbon content to the atmosphere as carbon dioxide. One would assume that a new equilibrium position would be reached beyond which no further net gain would be experienced. The limiting case of course is a a paddock full of mulch and eventually no soil.

    My experience with mulch is that over several seasons it completely disappears. As a consequence I assume that hungry bacteria have gobbled it up and as a consequence the carbon component has been returned to the atmosphere as exhaled carbon dioxide.

    Bio char by comparison may sequester the carbon content of the organic material for a much longer period, but the economic use of the existing material being diverted to another purpose will force up the price of the commodity. Again the limiting case is paddock for charcoal which won’t grow anything much.

    Overall there is no substitute for limiting fossil fuel and these proposals are at best a short term election fix.

  2. davidk

    I read about Barnaby Goose and find 20 comments, I read about Biosequestration and there is 1 co mment. I suppose Barnaby is sexier than biochar.
    I don’t understand why we can’t grow a crop, say lucern, and then plow it back into the soil. Then do it again, and again, and again. Doesn’t that take carbon out of the atmosphere and put it back into the soil without having to bake it, transport it or spread it.. I think gardeners call this green fertilizer.Would this create more bacteria?

  3. AR

    DaveK – as Greg pointed out, organic matter in soil is, sooner or later, rendered into its basic components and returned to the atmosphere, whether by bacteria, invertebrates or insects. It’s called the carbon cycle, without which this particular planet would be as fecund as mars or the Moon.
    This is assuming that the soil remains undisturbed. Plough or otherwise disturb it and the return to atmosphere accelerates.
    The surest & longest lasting, and thereby slowest, CO2 sequestration is trees. You know, those things that 200yrs of Oz farmers spent blood, sweat & toil on removing. Not only do we still pretend that this continent is suitable for European farming, until recently state governments gave grants, or COMPELLED landholders to ‘clear’ land.
    So bring on MM’s tree corps, it’ll give the unemployable urbanoids something to do, and remove them from delicate sight, when the faeces interfaces with the air movements device.

  4. mattsui

    Wonder if Mr Abbott has a plan to save water too……

    will our new pope sh*t in the woods?

  5. Evan Beaver

    David, the other reason we can’t just grow crops to store carbon is that the best places to grow these crops are also the best places to grow food. Create a competing and more lucrative alternative to growing food and the value of the land, and therefore the cost of food, goes up.

    Have a look at the US experience with biofuel subsidies. Apparently it drove the cost of corn through the roof.

  6. davidk

    @AR OK, we don’t plough the soil. But by growing a crop we remove carbon from the atmosphere. If we grow fast growing food crops without disturbing the groundcover would that not assist. I understand that trees are best, but they’re also slow.

  7. AR

    DavidK – slow is best. I have little interest in such “plans” because the vested interests 7 pig ignorance opposing implementation is huge.
    In short, any biological capture of carbon dioxide is going to release it some time. The fossil fuels are simply the vegetation from previous millenia (hence the term Carboniferous Age) – the problem at the moment is the release of this stored CO2 in a century when it was locked up over many millions of years. Sorta like uncapping a fizzy drink – which is a good analogy for the last 200yrs.

  8. davidk

    @ AR Thankyou, I understand