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Terrestrial Carbon Sink Variables

When CO₂ is taken in from the atmosphere by plants, the plant returns oxygen (O₂) to the atmosphere and keeps the carbon [C] to build roots, stalks, sap, and leaves. Part of this organic matter or organic carbon is preserved in the soil through the seasons and after the plant dies.

A number of factors affect the rate at which organic carbon can accumulate in soils. These factors include land cover and land use, land management practices, the biological activity within the soil, soil properties, the application of waste to the land, and climate.¹ Through an assessment and understanding of the primary variables governing soil carbon, the optimum factors that promote carbon accumulation can be determined. Of the processes mentioned above, a brief description is given below of the primary variables:

• Land Cover, Land Use, and Land Management Practices
  Land cover and land use represent the ecosystem type, such as agricultural land, wetlands, grasslands, and forestry. It is the properties of these associated ecosystems and the vegetation that are the indicators of potential carbon accumulation and the extent to which the soil-carrying capacity can be increased through ecosystem management.
• Soil Conditions
  Soil conditions discussed here incorporate the soil order, soil texture, drainage, and acidity of soil. These are regarded as the primary soil properties affecting the accumulation of soil carbon.² By knowing the soil order, the native environment under which the soil was formed can be determined, along with the soil's innate capacity to sequester organic carbon under ideal conditions.
• Land Resources
  The major land resource areas within the U.S. portion of the Plains CO₂ Reduction Partnership region are land resource units characterized by the Natural Resources Conservation Service. These land resource units represent geographic areas with similar soil, water resources, climate, vegetation, and land-use features.
• Climate
  Temperature, precipitation, and evaporation are key components in determining the rate at which soil carbon can be sequestered.^3,4

References:

1. Centre for Ecology and Hydrology (Natural Environment Research Council), CEH Project C01920, Environment Agency/National Assembly for Wales Contract 11406, Critical Appraisal of State and Pressures and Controls on the Sustainable Use of Soils in Wales; Final Report to Welsh Assembly Government, September 2002, on Behalf of the Project Consortium: CEH Bangor, National Soil Resources Institute, Institute of Grassland and Environment Research, Geoenvironmental Research Centre (Cardiff University), Cynefin Consultants http://www.bangor.ceh.ac.uk/English/reports/SSSFinalreport.htm
2. Cihacek, L.J., Personal communications, 2004.
3. Paustian, K.H.; and Cole. C.V., 1998, CO₂ mitigation by agriculture - an overview: Climatic Change 1998, v. 40, p. 135-162.
4. Lal, R., 2002, Soil carbon dynamics in cropland and rangeland: Environmental Pollution, v. 116, p. 353-362. Elsevier Science Ltd.