Friday, May 09, 2008

Perennial Pastures in Australia Shown to Sequester Carbon

The potential role for carbon sequestration in perennial pasture plants has received a boost with the release of some important research data that has put some quantified information into the public arena. The data is broadly supported by other information beginning to emerge from other parts of Australia.

Does this begin to really show that deep rooted perennial grass pastures can be effective in raising soil carbon levels? Is there a role for other grasses eg the very deep rooted Vetiver Grass used in mining reclamation for example. It does not address the issue of burning but there is some data about grazing.

Read the material below -----

Drought-tolerant perennial pastures could make a big dent in Australia's greenhouse emissions by helping soils to soak up carbon, says one researcher. But not everyone is convinced this approach really locks away as much carbon in the soil as claimed.

Tim Wiley, a pastures agronomist from Western Australia's Department of Agriculture and Food, says early findings from a trial of perennial pastures are "exciting". "They appear to have an exceptional ability to build up carbon in the soil," he says of the naturally drought-tolerant pastures. "If this preliminary data is right and you start extrapolating it over crop and pasture land in Australia, we could make a very big dent on Australia's emissions."

Soil carbon has decreased to between a half and a third its original levels since European agriculture was introduced. Today, 16% of Australia's annual greenhouse gases come from agriculture.

Wiley says trials of deep-rooted perennial sub-tropical grasses, such as Rhodes grass, on poor sandy soils in Western Australia show they can sequester much more carbon than traditional annual pastures.
He says results from a trial, which ran for more than three years on a farm in Lancelin, show Rhodes grass can capture and sequester nearly 7 tonnes per hectare of CO2 equivalents per year more than traditional pasture. CO2 equivalents are the units the Kyoto Protocol uses to measure greenhouse gases. The methane produced from the extra animals grazing on the perennial pastures only reduces this sequestration bonus by 10-20%, says Wiley.

Wiley says if these early findings are confirmed and the perennial pastures are grown on all suitable farmland in Western Australia, they could offset the state's entire annual greenhouse emissions.
He says the results are supported by data from farmers elsewhere in the area and trials across the country in Queensland.
This suggests the perennial pastures could have a similar effect in areas with very different rainfall and soils.

'Doesn't add up'

Dr Jeffrey Baldock, an expert in soil carbon sequestration from CSIRO Land and Water in Adelaide, agrees perennial pasture holds the best potential for increasing soil carbon and no one has ever tried to quantify its impact. But Baldock thinks the level of sequestration that Wiley reports doesn't add up. He says an increase of 7 tonnes of CO2 equivalents sequestered per hectare per year would require a massive increase in plant growth, measured as the amount of dried plant material. "For [Wiley's] carbon numbers to be correct he would have to be producing about 8 tonnes of extra dried Rhodes grass compared to the annual pasture," he says. "I'm not going to say it's impossible but it's a big ask."


Wiley says he has yet to complete a full measurement of dried plant material. But he says data gathered so far suggests the increase in dried material is not enough to explain the increase in carbon. He says the conventional assumptions that Baldock uses about how much carbon can be sequestered from plants into the soil could be wrong. He suspects the deep-rooted perennials are supporting a healthy crop of mycorrhiza, fungi living symbiotically on plant roots. Wiley says there is evidence that mycorrhiza are more effective than other soil microbes at producing humus and other stable carbon compounds in the soil, which Baldock disputes. But Baldock says more research of the kind that Wiley is involved in should be carried out.

Carbon trading

Wiley says he would not normally publicise such preliminary research but for discussions on whether to include soil carbon in Australia's greenhouse emissions trading scheme. He says soil carbon is already being traded in some parts of the world and while there are many uncertainties around how to measure soil carbon, findings such as his call for it to be included in a trading system.

Meanwhile, Baldock questions the economics of soil carbon trading, arguing that soil carbon should be increased simply because of the benefits it can bring productivity. "It increases water holding capacity, soil nutrition, provides carbon substrates for the soil microbial population to live on and enhances soil structural stability," he says.

[partially sourced from the ABC website]

All of the above about what carbon in the soil does is true. But we still need to get it there, and keep it there. For horticulture, the role of annual green manure crops is important, as a sensible means of building soil carbon and which has a direct and fairly immediate benefit to following horticulture crops. Can we both build and then keep adding to the soil carbon stores in other ways - with applied compost for example.

Both of these concepts are definitely NOT new. There is recent research data that indicates organic production can add to the soil carbon store. But that is really in most part, about the use of organic amendments, not necessarily the other factors in organic production.

legumes can be used as a green manure crop

Recycling organic waste, sequestering carbon, green manure crops, maintaining soil cover..........does one get a sense of deja vu? After all these were considered wise, prudent and profitable soil management considerations for most of the history of agriculture, especially since the Middle Ages, and most certainly taught in most agricultural science university courses world wide in the 19th and 20th centuries!

incorporating green manure crops on a large farm

Some more reading:

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