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Biochar's long-term benefits to soil proven

CARBON COPY: The Wollongbar site simulating an intensive dairy pasture used to test biochar's long-term effects upon the soil.
CARBON COPY: The Wollongbar site simulating an intensive dairy pasture used to test biochar's long-term effects upon the soil.

AFTER 10 years of intensive research, Southern Cross University and Department of Primary Industries scientists have for the first time quantified the long-term accumulation of carbon in soil following a single application of biochar.

The research, recognised and published in the international Nature Climate Change Journal, was conducted on 36 plots at the Wollongbar Primary Industries Institute.

Biochar derived from eucalypt residues was applied in 2006 into a pasture soil managed for intensive dairy production, with periodic cuts to simulate grazing.

Some plots had biochar with the green waste, others with cow manure and some with and without lime.

The lime - and the manure - increased the production of rye grass, which was sown, as on a normal dairy farm, every March/April.

The project's leader, DPI researcher and SCU adjunct professor Lukas Van Zwieten said the research threw up some unexpected results.

"We immediately saw an increase in soil carbon from the biochar, as expected, but what we didn't expect was that soil carbon content continued to increase.

"This research demonstrates the ongoing benefits of biochar in farming systems to improve pastures and grasslands and increase farmers' production and profitability,” Dr Van Zwieten said.

Biochar is produced through a process known as pyrolysis, which makes the organic carbon more stable to degradation.

Dr Van Zwieten said the researchers found that biochar enhanced the below-ground recovery of new root-derived carbon by 20% - that is, more of the carbon photosynthesised by plants was retained in the biochar-amended soil.

"Biochar accelerated the formation of soil microaggregates via interactions between organic matter and soil minerals, thus stabilising the root-derived carbon,” Dr Van Zwieten said.

That is, the improved structure of the soil protected the naturally occurring carbon, as well as the carbon added, said Southern Cross University's associate professor Terry Rose, a co-author of the study.

"Importantly, the biochar also slowed down the natural breakdown of native soil organic carbon by more than 5%,” Dr Rose said.

The increased microbial activity and improved physical structure of the soil would also ultimately improve the effectiveness of fertiliser use, Dr Van Zweiten said, making the application of biochar particularly beneficial for high-end, intensive crop production.

NSW DPI technical specialist Annette Cowie said the new findings were important for managing climate change, and for global CO2 accounting.

Application of biochar to soils could increase soil carbon sequestration and both help stabilise atmospheric CO2 concentrations and improve soil health and sustainability, she said.

The Australia New Zealand Biochar Conference will be held from August 10-12 at the Murwillumbah Civic and Cultural Centre and Showgrounds.

Topics:  biochar carbon farming soil health


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