Monday, September 22, 2008

CSIRO/GRDC: Costs too much to grow Soil Carbon

It will cost 4 time as much to grow soil carbon as you could hope to make from it, according to the GRDC and CSIRO. This truly incredible claim has moved many in the soil carbon community to question the science behind it.

The GRDC's Ground Cover article: "The hidden costs of sequestering carbon in the soil" (Passouria, CSIRO) seeks to prove that it would cost too much to grow soil carbon because of the price of nitrogenous fertilisers. "The C content of humus is about 60 per cent, so that every tonne of it contains 600 kg C (equivalent to 2.2 t CO2), and about 60 kg N, 12 kg P, and 9 kg S. Given that these amounts have to be locked up for as long as the carbon is stored, the question arises of what is the value of these required nutrients? The simplest assumption is that their value equals the cost of replacing them with fertiliser..."

The question has been framed to make the answer inevitable. The question should be, "Where can these required nutrients come from?" The source determines the prices. Once the frame is set, the next step is inevitable: "The simplest assumption" involves the application of expensive artifical fertilisers. After that shift, soil carbon is doomed.

"Carbon trading is normally based on a tonne of CO2 equivalent, of which there are about 2.2 tonnes per tonne of humus. Thus, if the trading price for CO2 is, say, $20 per tonne, then humus would be worth $44 per tonne. This is but a quarter of the estimated value of nutrients locked up, as shown in the Table."

The lead author kindly sent us an advance copy of the article, with these comments: "I am aware of Colin Seis's remarkable achievements, and I have wondered how he has succeeded in increasing soil organic matter in the topsoil by 2%. If that increase is largely humus, then it is likely to contain, in organically bound form, about 2 tonne/ha of N, 400 kg/ha of P and 300 kg/ha of S. I puzzle about where such large amounts could have come from."

Now he has asked the right question. Col Seis says the answer is: soil microbiology. "They should ask their own people," he says. "It's no mystery. The mystery is that they can completely ignore what goes on in the soil and write these articles."

Free-living nitrogen-fixing bacteria and symbiotic fungi can release and make available to plants vast amounts of the N, P, and S locked up in the soil after years of over-application of fertilisers. A CSIRO Fact Sheet says: "We know the current amount of nitrogen fertilizer applied per year is about 100 Megatons of nitrogen. However, we do not have an accurate knowledge of the amount of nitrogen addition through nitrogen fixation, although estimates are between 50 and 200 Megatons of nitrogen per year."(1) A NSW Department of Primary Industries fact sheet says, "Rhizobium bacteria ... can fix 100kg of nitrogen per hectare per year." (2)

In 1998, a CSIRO team claimed that Australian agricultural soils may be holding up to $10 billion worth of phosphorus, as a result of fertiliser applications. "The rural industry spends $600 million each year on phosphate-based fertilisers, yet often only about 10 to 20 per cent of the phosphorus is directly used by plants in the year it is applied," said CSIRO Plant Industry researchers Dr Alan Richardson and Dr Peter Hocking (3). "The remaining phosphorus becomes locked-up in the soil," he said.

If the right bacteria and fungi are present, more nutrient means more growth, which means more microbial activity and more biomass to enrich the soil. "When phosphorus is scarce in soil, plants that have developed mycorrhizas on their root systems have greater access to and take up more phosphorus others," according to the University of Western Australia's Soil Science Department.(4)

The belief that only by introducing organic matter from outside the system can organic carbon grow seems to dominate thinking in high places. But wasn't it superseded long ago? “Numerous studies have shown that the introduction of strains of [bacteria] into the rhizospheres of cultivated plants led to significant increases in grain yield as well as total dry matter... The stimulations observed are most likely due to the production of growth hormones by these bacteria." (5)

We have to answer every challenge. We believe that, if given a level playing field and bullet-proof scientific methodology, we can prove that carbon farming land management techniques, if properly applied, can result in accelerated rates of C sequestration.

(5) Davet, Pierrre, Microbial Ecology of the Soil and Plant Growth, 2004

No comments: