A new set of maps will establish a clear baseline for Australia’s soil organic carbon stocks.

Future changes in soil carbon storage or carbon sequestration can be effectively charted with the help of the new CSIRO-developed map.

Researchers have built the most detailed and accurate representation of soil organic carbon stocks to a depth of 30 cm across the entire country.

The map draws on soil sampling data and innovative prediction methods and includes estimates of soil carbon stock and potential uncertainty nationwide.

“This map is the first effective nationwide baseline of organic carbon levels in the top 30 cm of soil, which comes with estimates of uncertainty,” said lead researcher, Dr Raphael Viscarra Rossel.

“The map provides a reliable benchmark for Australia to monitor the influence that changes in land cover, climate, land management and greenhouse gas offset activities have on soil carbon stocks and associated carbon dioxide removal from the atmosphere.”

The map was compiled from three major datasets; CSIRO's National Soil and Spectral databases and the national Soil Carbon Research Program funded by the Australian Government and the Grains Research and Development Corporation.

The map highlights the broad diversity of soil carbon distribution in Australia.

“Australia's largest soil organic carbon stores per hectare occur in the cool, temperate zones, which have higher-than-average rainfall and extensive rainforests and eucalyptus forests,” Dr Viscarra Rossel said.

“These larger stocks of organic soil carbon tend to coincide with southern states and regions fringing the coastlines, where wetter and cooler conditions produce more vegetation growth with slower decomposition and loss of carbon dioxide. South Australia, due to its large amount of desert, is an exception; its soils contain the least amount of organic carbon per hectare, followed by northern and western jurisdictions and regions exposed to Mediterranean, subtropical and tropical climates.”

The average amount of organic carbon in the top 30 cm of Australian soil was estimated to be 29.7 tonnes per hectare and the total stock for the continent at 25.0 gigatonnes (Gt= 1000 million tonnes) with a 95 per cent confidence of being within the range of 19.0 to 31.8 Gt. The total stock in agricultural regions of Australia is 12.7 Gt with 95 per cent confidence of being within the range of 9.9 to 15.9 Gt.

The new work was published this week in the journal Global Change Biology.