[permaculture] Carbon Storage in Soil

Kirby Fry peace at totalaccess.net
Fri Nov 29 11:28:24 EST 2002


  Here's another article (part of it anyway) on the capacity of soils to store Carbon.  Notice the high rates of carbon accumulation for restoring degraded lands.

  The more I look, the more I learn that there is a well organized contigent advocating the restoration of degraded lands, who's recommendations and methods run contrary to the tree clearing ecosystem restorationists of Texas.  This Greening Earth Society could be a good lead.
* * * * *

  CARBON STORAGE IN SOIL: The Ultimate No-Regrets Policy? 
  A Report to 
  David E. Wojick, Ph.D., P.E. 
  Dwojick at shentel.net 

  November 1, 1999 

  Capacity for Soil Storage of Carbon

  There is tremendous capacity for storage of carbon in soil, both in the United States and globally. In fact, it is estimated that about 100 billion tons of carbon that was originally in the soil has been lost due to human activity, especially agriculture. Most of this carbon could be returned to the soil, improving the soil in the process. With mankind's annual carbon emissions estimated to be just 6 to 8 billion tons this signifies huge storage potential.

  World soils contain about 3.2 trillion tons of carbon within the top six feet. An estimated 2.5 trillion tons is in the form of soil organic carbon. This is the organic matter in the soil that makes it fertile. The remaining 0.7 trillion tons is soil inorganic carbon.

  These are very large numbers. In fact the soil carbon pool is 4.2 times the entire atmospheric pool, and 5.7 times the biotic pool. Thus, even a relatively small increase in soil carbon, if it is taken from the air, could provide a significant reduction in atmospheric carbon. Moreover, because plants feed on carbon dioxide (CO2) in the air, the primary way to store carbon in soil is to grow plants. Improved agriculture is the key to soil storage of carbon.

  Soil organic matter is concentrated in the upper 12 inches of the soil. So it is readily depleted by anthropogenic (human-induced) disturbances such as land use changes and cultivation. The magnitude of soil carbon depletion is increased by soil degradation, especially due to erosion. (See figure - Soil Carbon Storage Replaces Lost Carbon)

  Land use changes in forests, grasslands and wetlands have transformed large areas of the earth from relatively stable ecosystems to agro-ecosystems under extensive and intensive use. The introduction of agriculture involves land clearing, draining, sod breaking, cultivation, replacing perennial vegetation with annual crops, and fertilizing. These changes have had major impacts on carbon pools and fluxes around the globe. In the initial phases of these transformations, major losses of CO2 to the atmosphere occurred as soil carbon levels adjusted to reduced carbon inputs and increased soil disturbance.

  Intense pressure for production also has led to serious soil degradation through erosion and nutrient losses. These trends continue in many areas of the world. In the U.S. and other industrialized nations with available energy and technology, agricultural productivity has steadily increased, land degradation has slowed or reversed, and soil carbon pools have stabilized or increased. However, soil carbon levels are still well below pre-agricultural levels.

  It is estimated that a large part (75 to 80%) of the lost carbon can be re-sequestered in the soils of the earth. Of course the soil carbon storage capacity is finite. Moreover, ecological factors and management practices limit the rate of storage. Nevertheless, it is thought possible to achieve this storage over the next 25 to 50 years. Since most of the original productive capacity of the earth would be restored in the process, this is indeed the ultimate "no-regrets" climate policy.

  The following table shows estimates of annual global soil storage of carbon that might be sustained over the next 25 to 50 years. [Source: Carbon Sequestration - State of the Science, U.S. Department of Energy, Office of Science and the Office of Fossil Energy, February 1999 available on-line at http://www.fe.doe.gov/coal_power/sequestration/index.html.

       (carbon in billion tons per year) 
        Agricultural lands 0.85 - 0.90 
        Biofuel croplands 0.50 - 0.80 
        Grasslands 0.50 
        Rangelands 1.20 
        Forests 1.00 - 3.00 
        Deserts and degraded lands 0.80 - 1.30 
        Terrestrial sediments 0.70 - 1.70 
        Boreal peatlands and other wetlands 0.10 - 0.70 
        Total 5.65 - 10.1 

  These numbers compare favorably with total human carbon emissions due to fossil fuel combustion, which are presently estimated to be six billion tons per year.

  One of the key research questions is how long these rates of carbon storage could be maintained. Also, there clearly is some maximum capacity for soil storage, but that capacity is far from certain. Refining such estimates should be one of the central R&D tasks in any soil-carbon-storage program.

  While perhaps surprisingly large, these relatively high levels of potential carbon storage are not unreasonable. For example, a five percent increase in total carbon contained in global terrestrial ecosystems and agro-ecosystems over a 25-year period would store over 100 billion tons of carbon. Storing 100 billion tons over 25 years requires increasing the rate of storage by an average of only 0.2 percent per year - roughly one half of the amount estimated above.

Entir Article at:  http://www.greeningearthsociety.org/Articles/1999/carbon1.htm

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