GHG logo Welcome to GHG, a site devoted to greenhouse gas science and research

Carbon dioxide Sinks - Soils

Soils around the world contain approximately 2000 billion tonnes of carbon in various forms at any one time. About 300 billion tonnes can be found as detritus in the top soil, with this carbon rich material decomposing at varying rates depending on factors such as temperature and soil conditions.

During this decomposition some of the carbon in soil detritus is respired by the decomposing organisms (often fungi and bacteria), with the carbon being returned to the atmosphere as carbon dioxide.

The rest of the detritus carbon can be converted into 'modified soil carbon' which decomposes more slowly and so keeps the carbon from the atmosphere for longer. A small amount of this carbon is further decomposed to so called 'inert' carbon, as noted in the Biomass Burning Carbon dioxide page, and this can remain locked away from the atmosphere for over a thousand years.

Human Impact

As discussed in the page on Land-use change related carbon dioxide emissions, man's conversion of soils from natural to agricultural use has led to substantial losses in the soil carbon sink. Greater soil disturbance, such as that caused by ploughing, can cause rapid respiration and loss of large amounts of soil carbon which would otherwise decompose more slowly.

Potential for control

Sensitive land-use practice is key to better balancing the soil carbon sink, and perhaps reversing recent trends of loss of carbon from soils. Farming practices such as 'no-till', whereby agricultural land is used without the soil disturbance and carbon loss which comes with ploughing, are becoming more widespread and land-use remains a key area of research in studies of man-made greenhouse gas emissions and strategies to reduce them.

Contact the Author  •  GHG Online Home  •  Copyright  •  Content disclaimer