Global carbon cycle
There are various forms of soil carbon that are received, stored and emitted through the carbon cycle. Soil carbon may be very stable and stay in the soil for thousands of years or it may be broken down in just a few hours. Soil carbon stores are far greater than the atmosphere and plants combined.
Soil carbon can be found in both organic and inorganic forms. It is the principal ingredient in organic matter which is plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesised by them. It is made up of organic compounds such as sugars, starches, proteins, carbohydrates, lignins, waxes, resins and organic acids.
The Department of Environment and Resource Management (DERM) is involved in research activities looking at the effects of land management on greenhouse gases and carbon sequestration. This involves working with a number of organisations involved in soil carbon research including Queensland Primary Industries and Fisheries and Meat and Livestock Australia.
The global carbon cycle
There is as much carbon in the world today as there was millions of years ago. Human activities affect the global carbon cycle through the burning of fossil fuels and through interactions with the soil and vegetation carbon stores.
Image: Global Carbon cycle (adapted from Brady and Weil 2008)
Benefits of soil organic matter
Soil organic matter and soil carbon are a vital indicator of soil health. Soil organic matter impacts on a variety of soil functions and properties including:
- acting as an energy source for micro-organisms and as a reservoir of nutrients (i.e. nitrogen, phosphorus and sulfur)
- supporting soil structure by binding particles together into aggregates, which keeps the soil stable—increasing water infiltration and assists to prevent soil compaction
- increasing pH buffering capacity, which make soils less vulnerable to soil acidification
- negatively charged particles, attached to soil organic matter help to prevent leaching of important cations such as calcium, magnesium and potassium.
Improving soil carbon levels
Ways to improve soil carbon levels will vary according to land-use, soil type and climate. As Queensland is a large state there is a huge variation in the range of soil conditions.
Around 85 per cent of Queensland is used for grazing of pasture land. This area includes woodlands, forests, natural grasslands, and areas planted to exotic pasture species. General practices for improving soil carbon in grazing lands include:
- having pastures with perennial species; resulting in greater soil carbon inputs than annual plants
- a well managed pasture that has not been overgrazed or eroded can produce a higher rate of plant growth and be more capable of increasing the level of carbon in the soil.
Healthy crops convert the most carbon dioxide into plant growth. They need adequate water and nutrients, a well aerated, non-compacted soil, a neutral pH and a high level of biological life in the soil. Our farmers have been very selective in the land that they choose to grow crops as only two per cent of Queensland is used for cropping. Practices that promote soil carbon levels in cropping lands include:
- maintaining a healthy soil that makes optimal use of rainfall and irrigation, has adequate levels of plant nutrients, is well aerated, has a close to neutral pH and high levels of biological life
- minimising soil compaction by the adoption of practices such as controlled traffic farming (CTF)
- using green and brown manure crops (green manure crops sprayed with herbicide)
- adopting a pasture phase in a crop rotation system (preferably including a legume)
- adopting zero till or conservation farming practices
External related links:
- Industry and Investment NSW – Soil Carbon
- Tasmanian Department of Primary Industries, Parks, Water and Environment – Soil Organic Matter
- CSIRO – Soil carbon
Last reviewed 10 April 2012
Last updated 13 October 2010