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United States Department of Agriculture

Agricultural Research Service

Giving Farmers Credit for Carbon / April 22, 2005 / News from the USDA Agricultural Research Service

No-till cotton. Link to photo information
Traditional tillage releases soil carbon into the atmosphere as CO2. But conservation tillage helps store carbon in the soil by disturbing the soil less and retaining more crop residue, as in this no-till cotton field. Click the image for more information about it.

Giving Farmers Credit for Carbon

By Don Comis
April 22, 2005

Agricultural Research Service (ARS) soil scientists Jane Johnson and Don Reicosky in Morris, Minn., are all set to greet Earth Day today with greenhouse gas monitors in their corn, soybean, alfalfa and wheat fields.

They're based at the ARS North Central Soil Conservation Research Laboratory, one of 30 labs in the ARS GRACEnet--Greenhouse Gas Reduction through Agricultural Carbon Enhancement network. It monitors greenhouse gas emissions (carbon dioxide, nitrous oxide and methane) from cropland and pasture, with the goal of reducing these emissions.

Even a small increase in the amount of carbon stored per acre of farmland would have a large effect on offsetting U.S. greenhouse gas emissions. Farms and ranches have the potential to store enough carbon to offset 8 to 10 percent of total U.S. emissions. Decreasing nitrous oxide and methane emissions would be an additional offset benefit that agriculture could provide.

Data from all the GRACEnet experiments nationwide will provide a scientific basis for possible carbon credit and trading programs.

Johnson and Reicosky began monitoring in the northern winter because freeze-thaw cycles release nitrous oxide from soil. The Morris scientists monitor escaping gases by placing sealed chambers over various spots in the crop fields. They then take air samples from the chambers back to the lab for analysis of the captured gases with gas chromatography. Reicosky has previously used a large, tractor-mounted chamber to measure carbon dioxide losses from soil after tillage.

The scientists are comparing gases released by no-till and plowing, with and without fertilizer. The crops without fertilizer will get their nitrogen from a previous legume crop--either alfalfa or soybeans.

Network labs will document not only how much greenhouse gas farmland emits, but also how much soil carbon it stores and how much various practices--such as reduced tillage or reduced fertilizing--help lower emissions and increase carbon storage.

ARS is the U.S. Department of Agriculture's chief scientific research agency.

Last Modified: 4/22/2005
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