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A stocktake of soil organic carbon on the Esperance sand plain has shown that soils under annual and perennial pasture contained on average 45 tonnes of carbon per hectare to a depth of 30 cm.

Announced in Esperance on Friday, August 19, the results are the first revealed in WA from the national Soil Carbon Research Program, which will also assess carbon stocks at Young River, South Stirling, Kalgan-Woogenellup, Kojonup, Bunbury-Busselton, Northam-Avon and Mingenew-Irwin.

Funded by the Australian Government's Climate Change Research Program and the Grains Research and Development Corporation, the project confirmed that perennial paddocks established for about 30 years had soil carbon stocks from 30 to 80 t C/ha (average 49 t C/ha), highlighting the large variation between individual paddocks.

Modelling using realistic management scenarios suggested no further increase under annual pasture, while perennial pastures could reach on average 60 t C/ha over 40 years.

According to The University of Western Australia (UWA) Associate Professor Daniel Murphy, from The UWA Institute of Agriculture, an increase of 15 t C/ha over 40years, or 0.4 t C/ha each year, represented only a small gain in soil carbon stocks.

"Larger increases are very unlikely due to the low clay content of these sandy soils, which means that organic matter is less physically protected from breakdown by microorganisms," he said.

"Sustainable soil management, in particular soil organic carbon, is essential for the viability of Australian agriculture.

"Storing more carbon in soil has significant benefits for soil quality and can decrease levels of atmospheric carbon.

"The amount of organic carbon a soil can store changes between regions and is controlled by soil type, climate and management," Associate Professor Murphy explained.

David Hall, from the Department of Agriculture and Food WA (DAFWA), cautioned farmers interested in increasing carbon sequestration, as the Esperance results showed changes might be small and would occur slowly over time.

However, Mr Hall said the results from this and other studies showed that without restrictions to plant growth, long term annual and perennial pastures had similar levels of carbon storage.

"By comparison, clay amendment, common on the Esperance sand plain, lifted carbon storage by 2 t C/ha over 10 years when clay content of topsoil was increased  from 1 to 6 %," he said.

Associate Professor Murphy stressed that soil carbon storage actually referred to soil organic matter storage, meaning that when carbon was locked up in soil, there would also be other nutrients, such as nitrogen, sulphur and phosphorus.

"For example, sequestering 10 t/ha of carbon, tied up 1 t/ha of nitrogen and all the associated costs and benefits needed to be considered," he said.

"Achieving maximum carbon storage required maximum plant growth and maximum returns to the system and it was therefore important to employ practices that removed constraints to plant growth and ensured maximum returns of plant residues and animal manures, where affordable."

The stocktake by UWA and DAFWA researchers measured carbon levels at more than 100 sites on the Esperance sand plain before comparing them to model simulations for carbon storage in these soils.

Further information:

David Hall: Email [email protected] or Tel (+61) 8 90831111

Daniel Murphy: Email [email protected] or Tel (+61) 8 6488 7083

www.soilquality.org.au

Media references

Brendon Cant & Associates (+61) 8 9731 6739

Winthrop Professor Kadambot Siddique,

Director, The UWA Institute of Agriculture

(+61) 0411 155 396