Soil Has A Significant Role In Climate Change

March 10, 2000 The Rural News

Minimal soil tillage helps to reduce greenhouse gas emissions by keeping carbon dioxide locked in the soil and not contributing to global warming, according to a senior soil scientist with the New South Wales Department of Land and Water Conservation, Andrew Rawson.

A recent review of the scientific literature on carbon stores and global climate change by Mr Rawson and Brian Murphy of DLWC, Cowra, has shown the significant role soils have to play in global climate change.

"Soil is a primary component of the carbon cycle and often underestimated in the whole Greenhouse story," he said. "Soil management is just as significant as growing trees because soils may be the best long-term sink for the carbon extracted from the atmosphere by vegetation."

Mr Rawson said that soil is a "living" medium, which respires in much the same way as plants do. "Biological activity in the soil decomposes organic matter near the surface, converting some into CO₂ while storing parts of it as different forms of carbon in the soil," he said.

'Under natural conditions CO₂ released by the decomposition process eventually bubbles up to the surface and is released into the atmosphere. However, if you disturb the natural balance, carbon stays there. CO₂ is released very quickly, while the extra oxygen allowed into the topsoil also fuels more rapid organic matter decomposition, further degrading the stores of soil carbon," he added.

"Soil was also a major storage area for carbon which helped to "lock it away" from going into the atmosphere and contributing to global warming.

"Plants absorb CO₂ from the atmosphere and store it in their leaves, stems and roots as carbon, and when they die and rot into the soil, much of the carbon stays there."

"Carbon stays in the soil for an average of 32 years, although some forms of carbon can be locked in for up to 50,000 years," he said. Furthermore, the total global carbon store found in soils is greater than in both vegetation and the atmosphere combined.

Soil is quite clearly an extremely important store of the carbon and could be contributing to global warming if managed incorrectly. "There are many collateral benefits in restoring organic matter to soils such as improvements to soil structure, nutrient and water availability and resistance to erosion," he said.

"Land management options such a minimum tillage, replanting shrubs and trees in degraded areas, and reducing wholesale land clearing will undoubtedly not only help reduce our greenhouse gas emissions, but will also improve our soils. "The most important outcome of reforestration by far will be long-term improvements to organic matter in soils thus ensuring a healthy soil structure capable of improved levels of carbon retention." he said.