Currently little is known about the potential of soils to store carbon and the impact that management practices have on long term levels. To overcome this major knowledge gap DEWNR is collaborating with CSIRO in the National Soil Carbon Research Program. This project investigates the opportunity for farming systems that provide improved protection from soil erosion to also provide carbon sequestration
In total, soils contain about twice more carbon than the atmosphere and two and a half times more than all living things. This carbon comes in two forms:
- organic - from the organic sources such as plants, animals and microbes, and known as soil organic carbon
- inorganic - such as that contained in calcium carbonate (lime).
SOC levels are largely determined by three factors:
- the amount of biomass grown - rainfall, soil fertility and crop type determines the amount of plant biomass and hence the amount of organic material that can be potentially returned to the soils
- management - tillage of the soil reduces SOC by exposing it to microbes that break-down organic materials. Decomposition by microbes results in organic carbon being converted back into to carbon dioxide and returned to the atmosphere. Grazing or burning of residues also reduces the amount of organic material returned to the soils. Typically, pasture systems tend to have higher SOC levels than cropping systems.
- soil texture - clay protects the SOC from decomposition by microbes. The higher the clay content, the higher the potential for soils to store organic carbon.
See the 'Pools' (or types) of soil organic carbon fact sheet
The level of SOC in the soil is constantly fluctuating, responding to changes in organic material inputs and loss through microbial decomposition.. The speed of decomposition depends on the nature of organic material, soil factors (eg amount of clay) and climate factors.