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