Page Banner

United States Department of Agriculture

Agricultural Research Service

You are here: ARS Home / Research / National Programs / National Program 204 : Global Change / Component I: Carbon Cycle and Carbon Storage
National Program 204: Global Change
Component I: Carbon Cycle and Carbon Storage
headline bar
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
Introduction

Background

Carbon is the element that defines organic compounds, i.e., those derived from plants and animals, and is therefore at the core of life processes. It has been the object of a great deal of research, but much is still unknown about its cycling from the soil into the atmosphere and back into the soil. This cycle includes both organic and inorganic, i.e., derived from minerals, compounds. The increase in atmospheric carbon dioxide, a greenhouse gas, has heightened interest in carbon storage science because of the role of carbon dioxide and other carbon-containing compounds (methane and other hydrocarbons) in climate change. The concentration of carbon dioxide has increased in the Industrial Age from 270 parts per million (ppm) in the atmosphere in 1800 to the current 365 ppm. It is continuing to increase at a rate of approximately half a percent per year. The increase has been due partly to the burning of fossil fuels and partly to changes in land use and management, including deforestation, conversion of grasslands to croplands, and farming practices that accelerated oxidation, or breakdown, of soil organic matter.

Agricultural research has long focused attention on carbon cycling, primarily because of the fundamental role of carbon in plant development but also because of the importance of organic carbon compounds in maintaining soil tilth and productivity. Recently, in response to concerns about global climate change, a strong interest has developed in determining how agricultural activities and practices can be used to store carbon, particularly in soil. Scientific methodology to enhance soil carbon storage requires a holistic investigation of carbon cycle science. Soil carbon storage potential is the subject of both policy and scientific study. A federal multiagency research initiative on the carbon cycle, the U.S. Global Change Research Program Carbon Cycle Initiative, is under development to address carbon cycle science. ARS is participating in this initiative because agricultural activities have a major impact on the carbon cycle

Soil is the largest terrestrial global carbon pool, estimated to be about one-and-a-half trillion tons. This dynamic pool participates in an annual carbon dioxide exchange between the soil and the atmosphere 10 times as large as that emitted by fossil fuel use. In general, a balance is maintained between the carbon dioxide removed from the atmosphere by plants and the carbon dioxide returned to the atmosphere from the decomposition of plant and animal material. However, changes in land use and land management can disrupt that balance. When native forests and grasslands were cleared and plowed to grow crops during the westward expansion of the U.S., plant and soil organic carbon was rapidly decomposed to carbon dioxide; thus, cultivated agricultural ecosystems contributed to the increase in atmospheric carbon dioxide. On average, the carbon content of tilled soils in the U.S. has been reduced about 40% from pre-tillage levels. This historical loss now provides a pool that can be refilled by using management practices such as improved cropping systems, conservation tillage, grass buffers, and measures such as the Conservation Reserve Program (CRP) and wetlands. Soil carbon storage, then, could partially offset fossil fuel and other carbon emissions, at least until soil storage capacity is reached. Moreover, best management practices for both cropped and grazed lands improve soil resources while increasing carbon storage.

We need a better understanding of the dynamic path of carbon storage. The amount of carbon stored in the soil is determined by the balance of two processes--production of organic matter by terrestrial vegetation (photosynthesis) and decomposition (respiration) of organic matter by soil organisms. Each of these processes is controlled by physical and biological factors. For a given plant type, photosynthetic production depends largely on climate (solar radiation, temperature, rainfall), soil water status, nutrient availability, and carbon dioxide concentration, the latter providing a potential positive aspect of rising atmospheric carbon dioxide levels. Land use options for enhanced carbon storage include identification, protection, and selective management of the most productive native and agricultural ecosystems. Genetic improvements in vegetative photosynthetic capacities offer greater potential ecosystem capture of carbon dioxide and ultimate soil carbon storage.

Increased soil carbon storage is a co-benefit of conservation policies and efforts to reduce soil erosion on agricultural lands, which include the retirement of marginal or degraded croplands under the CRP and Highly Erodible Land conservation subtitles of the Food Security Act of 1985. This act allowed the voluntary retirement of more than 36 million acres of erodible lands for reseeding to perennial grass and tree covers. In addition, a projected two million miles of buffers along stream banks will be established to protect water from potential nonpoint source pollution. Key issues facing resource managers and policymakers are how to manage these vast resources for optimal economic returns while maximizing carbon stored under site-specific soil conditions and how to preserve much of the carbon pool upon termination of these programs.

Estimates indicate that each year in the U.S. about one-and-a third billion tons of carbon are removed from the atmosphere as carbon dioxide by the photosynthetic activity of agricultural crops. Furthermore, indications are that the North American continent is potentially a large repository for carbon. A portion of the fixed carbon within plants ultimately enters the soil, but the capacity of soils to store carbon, the length of time the carbon can be stored in the soil, and the rate at which carbon storage could be accomplished are matters of great interest to both scientists and policymakers. Because of the historical loss, there is no doubt that soil can serve as a carbon repository. Scientific studies have shown that proper management practices such as conservation tillage can increase soil carbon levels. The debate centers on the capacity of soils to store carbon while remaining in productive use and on the policies that will maintain agricultural productivity and maximize carbon storage and climate change benefits. If 5 -15% of the U.S. production of nonfood plant components in croplands were stored in soil organic carbon, an annual carbon storage rate of 70 to 200 million tons could be achieved. These are highly significant quantities of carbon, enough to store all the carbon dioxide emitted from agricultural activities and some of the fossil fuel emissions from other sectors of the U.S. economy. U.S. agriculture would be a net repository of greenhouse gases, helping to mitigate potentially harmful global changes.

Vision

Reduced risk of global climate change and enhanced soil resources through soil carbon storage research

Mission

Conduct and transfer the results of research to identify the best practices for storing carbon from atmospheric carbon dioxide in natural soil and plant systems to reduce greenhouse gases and enhance soil resources

Table 2. ARS locations contributing to the Carbon Cycle and Carbon Storage Component of the Global Change National Program

Global Change National Program

Components

State

Locations

Carbon Cycle and Carbon Storage

Trace Gases

Agricultural Ecosystem Impacts

Changes in Weather & the Water Cycle at Farm, Ranch, and Regional Scales

AK

Booneville

X

     

AL

Auburn

X

X

   

AZ

Phoenix

X

X

   

AZ

Tucson

X

   

X

CA

Fresno

X

     

CA

Riverside

X

     

CO

Akron

X

     

CO

Ft. Collins

X

X

 

X

FL

Gainesville

X

     

GA

Tifton

X

   

X

GA

Watkinsville

X

     

IA

Ames

X

X

   

ID

Boise

     

X

ID

Kimberly

X

     

IL

Champaign

X

     

IN

West Lafayette

X

     

MD

Beltsville

X

X

 

X

ME

Orono

X

     

MN

Morris

X

X

   

MN

St. Paul

X

     

MO

Columbia

X

     

MS

Oxford

X

   

X

MS

Stoneville

X

     

MT

Miles City

X

     

MT

Sidney

X

     

ND

Mandan

X

     

NE

Lincoln

X

X

   

NM

Jornada

X

 

X

 

NM

Las Cruces

     

X

OH

Columbus

X

     

OH

Coshocton

X

   

X

OK

El Reno

X

   

X

OK

Woodward

X

     

OR

Corvallis

X

     

OR

Pendleton

X

     

PA

University Park

X

 

X

 

SC

Florence

X

X

   

SD

Brookings

X

     

TX

Bushland

X

X

   

TX

Temple

X

 

X

X

TX

Weslaco

X

     

WA

Prosser

X

     

WA

Pullman

X

X

X

 

WV

Beaver

X

     

WY

Cheyenne

X

     

[1]     2     3     4     5     6     7     8     9     Next >>

Last Modified: 10/28/2008
Footer Content Back to Top of Page