Greenhouse Gases
Soils affect many of the processes that
can mitigate or exacerbate global change.
Many CSREES activities relate to the potential
for soil to serve as a sink for greenhouse
gases.
Carbon and
nitrogen cycles
The most important
greenhouse gases are carbon dioxide (CO2),
nitrous oxide (N2O), and methane
(CH4). While these gases have
many non-agricultural sources, soil organisms
and soil conditions play a major role in
the consumption and production of these
gases. Judicious management of soils can
have a tremendous potential for helping
to control or reduce these gases.
Soil microorganisms control many of the
processes that transform organic carbon into
the greenhouse gas carbon dioxide. At the
same time, soils supply support, water, and
nutrients necessary for plants to grow and
fix carbon dioxide in organic form. Soils
can also be either a source (chemical reduction)
or sink (oxidation) for methane, another
carbon-containing greenhouse gas, depending
on soil conditions, such as wetness, microbial
community, crop productivity, and soil chemical
and physical properties.
Many nutrients, including nitrogen, are
recycled into usable forms by soil microorganisms
and/or are stored and held against loss to
ground and surface water by soil particles.
Atmospheric nitrogen is fixed in organic
form through free-living soil organisms and
by symbiotic associations of soil microorganisms
and plants. Organic nitrogen can then be
mineralized to ammonia and oxidized to nitrate
(both usable by plants) by soil microorganisms.
They can be transformed to nitrogen gas and/or
the greenhouse gas nitrous oxide by other
microorganisms. The balance of these processes
and potential of soils to exacerbate or mitigate
greenhouse gas concentrations in the atmosphere
depends on physical, chemical, and microbiological
properties of soils, as well as climatic
conditions, soil and crop management practices,
vegetation, and atmospheric composition.
CSREES supports research, education, and
extension activities in all of these areas
through competitive and non-competitive grants
and through collaboration with our land-grant
partners and in interagency cooperation and
planning.
Ecosystems
Soils
and soil organisms form an integral part
of natural and managed ecosystems that can
be altered by climate change and can affect
the concentrations of greenhouse gases through
respiration, sequestration, and photosynthesis.
The various components of ecosystems all
interact to determine the overall response
of the system to changing climate and atmospheric
composition, as well as the feedback to the
atmosphere to mitigate or exacerbate potential
future climate change. Each type of ecosystem
in each different region, soil type, and
type and level of management may react differently
to changing conditions.
CSREES supports research, education, and
extension activities aimed at understanding
and eventually being able to predict and
manage these effects through competitive
and non-competitive grants and through collaboration
with our land-grant partners and interagency
cooperation and planning (see the Selected
Results and Impacts section of the Soils Program page).
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