Soil Carbon

Information for this section has been sourced from A Review of Carbon Sequestration in Vegetation and Soils: options, opportunities and barriers for the Southern Slopes Cluster NRM organisations developed by SCARP. The report can be found at www.climatechangeinaustralia.gov.au/en/impacts-and-adaptation/southern-slopes

Soil carbon is essential for soil health. It assists in soil structure and provides food for soil microbes that in turn benefits plants and helps regulate nutrient cycling. The amount of soil carbon varies across the south-westgion with peat soils in the region’s southwest at levels greater than 10% through to areas with high cultivation histories where the carbon level is typically less than 1%. This variation is a result of many factors, namely:

  • Soil and vegetation type, which determines the carbon-holding capacity
  • Climate, especially rainfall and temperature which determine the rate of decomposition
  • Land management practices, both current and historic

In general terms, higher soil organic carbon is likely to be found in areas of higher rainfall where traditionally perennial pastures have been used (i.e. dairy areas), whereas lower rainfall areas with annual cropping rotations have lower soil organic levels. A recent study by the Woady Yaloak Catchment Group on 950 soil samples collected over 20 years indicated the majority of results fell in a band of between 2.0% and 3.5% and cropping tended to decrease and perennial pastures increase total soil organic carbon (Woady Yaloak Catchment Group, 2012). The amount of carbon in soil can be maintained or increased with the rate of loss influenced by the:

  • The amount and type of organic matter, both plant and animal, entering the soil
  • Management practices which reduce carbon inputs, increase losses and/or increase decomposition rates. Examples include cultivation, stubble removal and overgrazing
  • Climate conditions such as rainfall, temperature and sunlight
  • Soil properties, including the clay, silt or sand content

The natural perennial vegetation cover that existed prior to European settlement declined as a result of traditional farming practices along with the region’s soil organic carbon. Since the 1990s, the region has made great progress in adopting more perennial based grazing systems and encouraged minimal cultivation cropping.  Industry groups such as Sustainable Grazing Systems, Evergraze and programs delivered by the state government have led to more land management practices that have minimised carbon losses. An interest in soil carbon sequestration has also led to this shift in land management. There are three main practices to improve soil carbon in the region’s soils. These are:

  • Grow pastures, crops and trees to maximise above ground biomass and root production while fitting the farming system.
  • Retain as much existing soil carbon as possible.
  • Use carbon rich sources or practices that increase soil function (biochar, humates, biological products, biosolids, green manure, high carbon using crops).

More information on soil organic carbon potential can be found in the "Brown Book", a sustainable agricultural information resource for the region. It addresses the needs of farmers to develop simple solutions in effective management of soils to enhance productivity, including soil organic carbon. More information on the Brown Book can be found at www.ccmaknowledgebase.vic.gov.au/soilhealth/brown_book/home