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United States Department of Agriculture

Agricultural Research Service

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National Program 204: Global Change
Component I: Carbon Cycle and Carbon Storage
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1 - Introduction
2 - Cropping System and Tilage
3 - Grazinglands, CRP and Buffers
4 - Irrigation and Water Managment
5 - Plantation Tree Farming
6 - Organic Carbon Transformations
7 - Inorganic Carbon
8 - Interactions of Carbon and Nitrogen Cycles
9 - Measurement, Validation and Modeling
Organic Carbon Transformations

Problem Statement

Rationale. Soil is the largest reservoir of carbon in terrestrial ecosystems. Understanding the mechanisms and processes involved in the accumulation and loss of stored soil carbon provides an opportunity to develop management strategies that increase carbon storage and decrease carbon loss.

What is known. Carbon is stored in the soil in both organic and inorganic forms. Neither the organic nor inorganic pools is homogeneous; both are composed of multiple compounds with a wide range of activity within the carbon cycle. Storage of organic carbon in the soil begins with the entrance of plant- and animal-derived material into the soil. Soil microorganisms control organic carbon cycling and storage in the soil by decomposing dead plant and animal matter and releasing carbon dioxide back to the atmosphere. Important factors regulating this microbial activity include the physical and chemical properties of the plant and animal materials entering the soil, the physical and chemical properties of the soil, and climatic conditions (e.g., temperature and precipitation).

Gaps. The above known factors need better definition as they relate to soil carbon storage. To enhance soil storage of organic carbon, we need to better understand the soil ecology (i.e., how the physical, chemical, and biological factors of the soil interact and affect each other). For example, soil aggregation processes contribute to the physical protection of soil organic carbon, but the relationship between the biological and chemical processes involved in soil aggregation is not well understood. Also needed is a better understanding of physical processes (e.g., erosion, fire, or leaching) by which organic carbon is lost from the soil.


  • Determine the factors controlling the rate, mass, and timing of carbon dioxide sequestered by plants and the amounts and biochemical composition of plant compounds partitioned to above- and below-ground plant organs;
  • Determine the fate of plant carbon within the soil, including the spatial distribution of plant carbon originating from above- and below-ground plant organs;
  • Determine the processes involved in the physical, chemical, and biological decomposition and transformations of plant-derived carbon;
  • Determine the rate of production and turnover of short-, intermediate-, and long-term soil carbon pools;
  • Determine the processes and mechanisms of soil carbon loss and transport, including understanding of on-site and off-site impacts; and
  • Determine the impact of elevated atmospheric carbon dioxide and climate change on biochemical composition and changes in plant structure and on soil carbon storage processes.


We must use and assess new and emerging technologies to conduct basic and applied laboratory, greenhouse, and field research to fill identified knowledge gaps. Collaboration among research scientists is necessary to integrate research on the mechanisms and processes of carbon storage, model development, and the development of management practices to enhance soil carbon storage. Interdisciplinary approaches will be important in this research. Archived soil samples from previous studies can be reassessed to glean information on soil carbon changes related to specific long-term management practices. This effort also can benefit from literature searches of past studies on soil organic matter and soil carbon changes related to land use and management practices within land uses. Results of these searches can be used to assess the subsequent effects of these management practices on carbon storage potential. Adjacent sites with similar soil but known long-term differences in land use or management practices should be identified to allow comparison of differences in stored soil carbon.


  • The uptake of carbon by plants will be increased, and improved strategies will be developed to store plant carbon as soil organic carbon;
  • The amount of plant carbon stored as soil organic carbon will be increased through alteration of the quantity and quality of plant carbon in roots, root exudates, plant residue, and litter;
  • The mechanisms and processes controlling uptake, decomposition, storage, and losses of soil carbon will be more predictable;
  • Factors that control the production and turnover of various carbon pools under agricultural systems will be more predictable, which will contribute to useful approaches for storing carbon;
  • Improved information will be made available on soil erosion, overland movement of carbon, losses of dissolved carbon, losses during burning, and losses from degraded and degrading soils; and
  • Management strategies will be developed to protect soil inorganic carbon.


Enhanced soil and plant productivity with maximum soil carbon storage

Linkages to Other ARS National Programs

  • Integrated Agricultural Systems
  • Rangeland, Pasture, and Forages
  • Soil Resource Management
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Last Modified: 10/28/2008
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