Models Unreliable

The opposition to the contention that Australian soils can sequester significant amounts of Carbon – and quickly – rests on ‘models’ that contain the data produced by scientists to date: data from conventional land management and some low-intensity techniqes like minimum tillage and no-tillage.
When the government asks scientists about the potential of our soils, the scientists consult the models – and give the only answer they can give: the potential for change in soil Carbon is for small amounts over long periods. But the accuracy of these models has been questioned by a senior government scientist. Dr Peter Fisher of the Victorian Department of Primary Industries found that Australian soils can sequester carbon 6 to 10 times faster than the models allow*. The models have for a long time been questioned by practitioners whose reults contradict the peer-reviewed data. Dr Fisher explains: “Modelling also suggests that under many Australian circumstances it may be impossible to increase TOC levels in agricultural soils, although this is in contrast to an increasing number of growers who are claiming to have made substantial improvements in SOM in relatively short time periods. … Some of these differences may be due to comparisons between modelling results based on typical practices and results, compared with individual growers whose management practices are atypical and well above those of the district norm. However, there is a need for much greater evaluation of both the claims made by growers and the assumptions that underlie modelling results.”
A series of articles in the Australia Farm Journal call into question the usefulness of the Roth C model (in its current configuration) for predicting the soil C performance of soil. It ignores the contribution of microbial communities. The articles take a long look at "The hidden costs of soil carbon" - a short paper by 5 CSIRO scientists which 'proved' that landholders could not afford to grow humus because of the cost of Nitrogen, Phosphorous and Sulphur inputs. The paper was based on a premise that is widely believed in soil science community: that the carbon sequestration potential of a soil is limited to the amount of organic matter added, ie. stubble retained, manure spread "The current configuration of a soil carbon model called Roth C suggests there would need to be 20 to 30 tonnes/ha/yr of biomass input to achieve the higher carbon sequestration rates we have measured under some perennial grasses in the Northern Ag Region of WA.," says Tim Wiley from the Department of Agriculture & Food, WA. But, while putting on an additional 16 tonnes of soil carbon/ha under perennials (vs annuals), the measurements of above ground biomass have been only 10 tonnes/ha/yr. Had the hypothesis of the CSIRO paper been right, there should have been a shortage of plant available Phosphorous under the perennials, with the extra tonnes of carbon sequestered binding more than 300kg/ha. But plant available P increased by 43kg/ha. This increase in P was also experienced by Scott Macalman at Warren.
The CSIRO Paper is misleading. Yet it was sent to 37,000 growers by the GRDC as part of its sustained campaign against the idea that farmers could ever be paid for growing soil carbon. The paper reveals that the analysis did not take into account the emerging knowledge of soil microbiology. It assumed that there could be no other source of nutrients than a bag from a fertilizer company. The formula for humus means you need 60kg of N, 12kg of P and 9kg of S for every tonne of humus you make. One of the paper's authors used this additional nutrient requirement to call into doubt Col Seis's 2% increase in soil carbon over 10 years.
It is out a paradigm at present, but soil biology is becoming popular inside both CSIRO and GRDC. 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."** A NSW Department of Primary Industries fact sheet says, "Rhizobium bacteria ... can fix 100kg of nitrogen per hectare per year."***
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****. "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 phosphorous than others," according to the University of Western Australia's Soil Science Department.*****
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 this idea 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."******

* Dr Fisher is saying the modelling suggests a 2t/ha increase in organic matter input for the same conditions, results in a change in soil carbon value of about 0.13pc after 20 years. However his research indicates that a 2t/ha increase in soil organic matter might result in approximately a 0.4pc change after only 10 years. Now 0.4pc is 3 times as much as 0.13pc, and 10 years is twice as quick as 20 years - so this is still a factor of 6 times better. And this on places where the farmers were not even focussed on building soil carbon."
** http://www.csiro.au/resources/GlobalNitrogenFixation.html
*** http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0005/41639/Microbes_and_minerals.pdf
**** http://www.csiro.au/files/mediaRelease/mr1998/Raiding10BillionPhosphorusBank.htm
*****http://www.soilhealth.segs.uwa.edu.au/components/fungi
****** Davet, Pierrre, Microbial Ecology of the Soil and Plant Growth, 2004