Published: 15 Mar 2022
A new university study has destroyed the idea that soil carbon sequestration will be the silver bullet to reduce Australia’s greenhouse gas emissions.
In fact, a warming climate will mean that the soil’s ability to retain soil carbon will be diminished over time, making soil carbon markets a “dangerous” place for farmers, a leading independent scientist said.
The University of Melbourne and University of Tasmania study has found that within 30 years, soil organic carbon sequestration rates will have “declined by 45-133 per cent, heralding dire ramifications for nations aspiring to capitalise on enhanced soil carbon sequestration as an avenue for emissions mitigation”.
University of Tasmania’s systems modelling team leader Associate Professor Matthew Harrison said today findings of a multidisciplinary research report – called Carbon, cash, cattle and the climate crisis – showed that as the climate warmed, the speed at which carbon was respired from soil also increased.
Although pastures may grow at a faster rate above ground, this did not mean soil carbon was stored at faster amounts below ground in a changing climate, he said.
Research was showing that instead, the rate at which soil carbon was stored was expected to decline over time.
Further, soils could not continually build soil carbon – once they reached the maximum amount of approximately five per cent organic carbon.
With many soil carbon markets requiring 25 year storage of carbon, Prof Harrison said it was also highly likely that an event such as drought could deplete soil carbon.
“There is a lot of hype out there about soil carbon, but for farmers to be thinking about trading or selling their soil carbon, I’d say that is a dangerous place to be,” Prof Harrison said.
This comes following warnings from other independent scientists and commercial farmers, reported by The Weeky Times last year, that productive agriculture would not be able to supply soil carbon to sell off credits, or prop up other industries to offset their emissions.
Then, those scientists said agriculture would require all its own offsets to balance its own environmental books.
Prof Harrison said the new work conducted by the Tasmanian Institute of Agriculture, which was being replicated in Victoria, NSW and Queensland projects, also highlighted the instability of soil carbon.
“I completely agree with those warnings (around soil carbon trades),” Prof Harrison said.
He said while it could appear appealing to farmers to sell carbon credits “and get a big cheque”, they needed to ask what happened when consumers who they supply products to demanded a carbon neutral product.
Farmers needed to be aware that they could not double-dip on carbon credits – get paid by a third-party for the environmental benefit, but also claim it for their own enterprise.
“If you sell the soil carbon, you cannot yourself claim your product is carbon neutral as well,” he said.
While the study’s findings about a reduced rate of soil carbon sequestration over time were based on high rainfall areas in Tasmania, Prof Harrison said similar studies in Victoria, NSW and QLD showed similar, if not “worse” trends.
Prof Harrison said that society would increasingly demand emissions abatement from the livestock sector, with one in four consumers now willing to pay 15 per cent more for carbon neural food.
The study, which examines the nexus between productivity, profitability and greenhouse gas emissions of farms in Tasmania under increasingly variable climates, also found, even with “explicit account of climatic extremes, climate change to 2050 will have minimal effects on livestock production and profit”.
It showed “mitigation, rather than adaptation, resulted in the greatest improvements in profitability”.
Even without adaptation, and accounting for more frequent extreme weather, annual pasture growth in Tasmania would lift to 2050 due to warmer winters and elevated atmospheric carbon dioxide.
While this would lead to a small lift in productivity, it would also raise farm GHG emissions, while reducing supplementary feed costs and increasing cash flow.
The report also “highlights the need for demand-driven research” matched to practical on-farm solutions.
STEPS TO NEUTRALITY
Prof Harrison said livestock farmers aiming for carbon neutrality – or net zero – should first focus on reducing methane as it was normally the largest portion of GHG, followed by planting trees, improving soil carbon then planting deep rooted legumes.
The first step was to identify the enterprise’s major emissions.
In the case of livestock production it was likely to be methane, and supplements such as red algae could great intensive feeding systems, like a feedlots.
There were, as yet, less reliable supplements to reduce emissions from extensive grazing.
More research was needed here – as well as practical application of the technology on-farm with consideration to cost and incentives for farmers – he said.
The federal government was expected to release a program where farmers would be paid to mitigate emissions (as opposed to carbon credits), later this year, he said.
The next step was to look at avoiding producing so much GHGs in the first place.
MORE EFFICIENT PRODUCTION
By lifting the efficiency of how beef or sheepmeat was produced, emissions would also be reduced per unit production, Prof Harrison said.
For example, turning off finished lambs (through best practice management, feeding and genetics) in a shorter time period reduced the amount of methane produced per kilogram of meat.
Offsetting emissions was another avenue, which involved paying someone else to reduce their carbon footprint without changing your own, however Prof Harrison advised against this.
CONSIDER LOCATION AND RAINFALL
Depending on the farm’s location, Prof Harrison said options like planting trees or shrubs, or agroforestry could also contribute to an enterprise’s steps towards carbon neutrality.
Higher rainfall zone farmers may find co-benefits of plating shelterbelts, and agroforestry could also be viable. Lower rainfall zones could use shrubs, while in northern areas, deep rooted legumes could also boost livestock production while reducing methane production.
The bottom line was there was no “blanket solution” for all enterprises that aimed to reduce their environmental impact.
Carbon neutrality would be achievable for many livestock farmers, but would require a big focus on methane and farmers were urged to not become too distracted by soil carbon trading, Prof Harrison said.