Soil stores carbon
More carbon is stored in the soil than in the atmosphere or in above ground vegetation. Soil is a complex substance made up of minerals, water, and organic matter. The soil organic matter is where over half of the carbon is located. It is made up of dead, living, and decomposing plants, animals, and microorganisms and of the organic compounds that result from the decomposition of these materials. It is the organic matter in soil that makes the soil fertile and able to grow plants. When this organic matter is decomposed, carbon dioxide is released into the atmosphere as a by-product of decomposition. When nitrogen is added to a field as nitrogen fertilizer or as animal manure, nitrogen can be lost to the atmosphere as the greenhouse gas nitrous oxide.
Release of greenhouse gases from soil
This release of greenhouse gases into the atmosphere is only a problem if it is excessive. When forest and grassland are cleared for farming, previously buried soil particles get brought to the surface, broken up, and exposed to the atmosphere. Clearing the vegetation causes the temperature and moisture content of the soil to change. The organic materials that used to fall onto the soil surface to decompose and become part of the soil have been carried away. Without the protection of vegetation, there is increased erosion. We have probably all seen mud running off of a construction site after a storm. That is the soil eroding away. Conventional farming has a similar effect. Tillage causes a release of carbon and soil erosion. Crops take up nutrients from the soil when are then carried away as produce.
Global warming effects
Global warming is expected to increase the release the greenhouse gases from soil as they become warmer. This will also cause soil to loss of soil fertility and enhanced erosion. This problem could be worse with frozen Arctic soils, or permafrost. The plant and animal material in the permafrost could decompose to release carbon dioxide or release methane in waterlogged areas. Methane is considered to be a more powerful greenhouse gas than carbon dioxide and its release could add several degrees to the global temperatures. Clearing of peat soils for agricultural use could lead to similar problems as the organic material in them decomposes.
Using soil to counteract global warming
On a positive note, soil can also be used to store carbon through reduced tillage, reduced fertilizer use, and careful management of forests and grasslands. Some areas are attempting to reforest watersheds in order to restore soil fertility. Researchers are examining different tillage and fertilization methods to determine which ones result in the lowest greenhouse gas emissions. Some researchers have proposed that storing carbon in soil can be used to offset industrial emissions of greenhouse gases. New crops are being looked at as carbon sinks. New methods are being developed to return crop residues to soil for carbon storage.
While soil is an important part of the climate change picture, it is only one part. Climate change is a complex, interdisciplinary problem with a lot of unknowns. Our knowledge continues to develop in this area. It will be interesting to see the new developments and knowledge that comes from research in this field. Here are some references to use as a starting point if you would like to do more reading on this subject.
* * *
“Global Warming Is Changing Organic Matter In Soil.” Space Daily. United Press International. 2008. AccessMyLibrary. 14 Dec. 2009 http://www.accessmylibrary.com.
Porteous, James; Steve Davidson,. “Saving the life of farmland soils: aware of a remorseless decline in the vital organic matter of Australian farmland soils because of land clearing and agricultural production, researchers, land managers and now, commercial players, are seeking ways to reverse the trend. It’s an important quest:without organic matter, soil is essentially sterile, reducing the viability of both agricultural and surrounding natural systems.(SOIL CARBON: Focus).” Ecos. CSIRO Publishing. 2006. AccessMyLibrary. 14 Dec. 2009 http://www.accessmylibrary.com.
Alan Sundermeier, Randall Reeder, and Rattan Lal. “Soil Carbon Sequestration Fundamentals, AEX-510-05”. The Ohio State University
“To What Degree? What Science is Telling Us About Climate Change”. National Science Foundation. 2009.
– Sydney Harper, December 2009