LIVESTOCK producers may have an emissions trading lifeline with the discovery that Australian soils are capable of neutralising more methane than cattle can produce from the same land.
Although only a preliminary finding, University of Sydney researchers have added a piece to the global warming policy puzzle.
How does methane produced by ruminant animals fit into the biological cycle?
Their research, done on grazing land in the Snowy Mountain region on soils with high organic matter levels of 5-7 per cent, found that these high country soils oxidise methane at a rate of 100 milligrams per square metre per hour, or roughly 8760 kilograms per hectare per year.
By contrast, 100 head of cattle produce about 5400 kg/ha of methane a year.
“In other words, high country grazing is easily methane-neutral and may even offset cow-methane from other parts of the landscape,” said Professor Mark Adams, Dean of Sydney University’s Faculty of Agriculture, Food and Natural Resources.
However, Prof Adams said more work is needed to tighten up his “back of the envelope” calculations, and to determine exactly what is happening in the soils being studied.
Nor is soil oxidation of methane an end to livestock emissions.
Prof Adams explained that a specific class of bacteria uses methane as part of its metabolic process. In oxidising methane, the bacteria produces another greenhouse gas, carbon dioxide (CO2).
But because methane is considered to have 23 times the greenhouse gas warming potential of CO2, the soil oxidation process, if considered part of a biological cycle, has the potential to cut the cost of livestock emissions by 23 times.
Prof Adams described the process as “very significant, and very consistent” across the high organic matter soils studied on the Snowy and Bogong high plains.
The methane finding was an unexpected outcome of a study established to look at interactions between grazing and bushfires.
“We reasoned that we also needed to know a little about how land management was going to affect greenhouse gas emissions, including what we thought would be methane emissions from the soils,” Prof Adams said.
“Lo and behold, we didn’t have methane emissions, we had methane oxidation.”
The study wasn’t the first to observe oxidisation of methane by soil microbes, Prof Adams said, but it is the first to measure the phenomenon in Australian soils.
“We don’t have a good handle on the conditions that promote the growth of methane-oxidising bacteria; we don’t know the exact nature of the microbial communities, we don’t know what else we could do to encourage them.”
“We know little, and in the world’s literature on this, there’s not much more than a handful of publications.”
However, Prof. Adams believes that the soils most capable of oxidising methane are likely to be well-drained, with good structure, rich in organic matter, and will not have been heavily treated with fertilisers known to kill off microbial life.
“Broadacre, low-intensity grazing operations might be something that Australia might well become specialised in as being more carbon-neutral. We could perhaps develop markets for beef or lamb produced using very little fossil fuels, and in a completely carbon-neutral way.”
“There’s much more potential significance to this, if we can get our story right, and our land management right.”
A Sydney University proposal to extend its research into soil oxidation of methane was rejected by the Federal Department of Agriculture.