Climate Change Mitigation Possibili-ties through Carbon Sequestration in the U.S.

The United States is an active player in the international effort to combat climate change.  Although 84% of US net carbon emissions come from fossil fuel consumption and only 7% from agriculture<!–[if supportFields]> XE “agriculture” <![endif]–><!–[if supportFields]><![endif]–>, the changes made in the agricultural system to fight climate change are still essential until new technologies and strategies become prevalent.  Agriculture is both largely affected by climate change, as well as a large contributor itself to the growing problem.  The management of agricultural systems to sequester carbon dioxide as soil organic carbon<!–[if supportFields]> XE “soil organic carbon (SOC)” <![endif]–><!–[if supportFields]><![endif]–> (SOC<!–[if supportFields]> XE “soil organic C, SOC” <![endif]–><!–[if supportFields]><![endif]–>) and to minimize GHG emissions is a partial solution for climate change mitigation.  Morgan et al. examine the various agricultural sectors in the United States for their SOC potential, distinguishing the different land characteristics. —Whitney Dawson
 Morgan, J.A., Follett, R., Hartwell Allen, L., Del Grosso, S., Derner, J., Dijkstra, F., Franzlubbers, A., Fry, R., Paustian, K., Schoeneberger, M., 2010.  Carbon sequestration<!–[if supportFields]>XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–> in agricultural lands of the United States.  Journal of Soil and Water Conservation 65, 6A–13A.

Morgan et al. (2010) explain that the rate of carbon return to the atmosphere is influenced by the rate of photosynthetic carbon dioxide assimilation, which is dependent on soil fertility, climate, and management.  Greenhouse gas mitigation is possible through assimilation of atmospheric carbon dioxide by vegetation<!–[if supportFields]> XE “vegetation” <![endif]–><!–[if supportFields]><![endif]–> choices, and moving carbon from plants and animals into soil.  Sequestering carbon within the soil organic matter<!–[if supportFields]>XE “soil organic matter (SOM)”<![endif]–><!–[if supportFields]><![endif]–> (SOM) is a prime option for carbon storage but has other benefits as well, such as improved soil quality, soil structure and stability, and water holding capacity.
The authors study each agricultural sector, picking apart possible improvements, and recognize valuable questions to be answered.  To increase SOC<!–[if supportFields]> XE “soil organic carbon (SOC)” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “soil organic C, SOC”<![endif]–><!–[if supportFields]><![endif]–> in croplands, the authors recommend increasing cropping frequency, growing high-residue crops, maximizing plant water use, and applying vegetation<!–[if supportFields]>XE “vegetation”<![endif]–><!–[if supportFields]><![endif]–> to shade the surface soil.  Grazing lands take up about 37% of total US land area and contribute about 15% of US soil carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–> potential.  The amount of carbon stored in grazing<!–[if supportFields]> XE “grazing” <![endif]–><!–[if supportFields]><![endif]–> lands can be double that of cropland and can be intensified by adjusting stocking rate, plant species, and fertilizer<!–[if supportFields]> XE “fertilizer” <![endif]–><!–[if supportFields]><![endif]–> use. Sequestration rates decline in grazing lands over time without added inputs, therefore attention to these areas is key.  Agro forestry is the integration of woody plants into crop and livestock systems for improvement of the quality of their environment, while still allowing sustainable production of food.  This system sequesters a large amount of carbon and for a long duration.  Horticulture land has received little attention for the potential of carbon sequestration<!–[if supportFields]>XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–> in its vegetable, vineyard, and orchard crops.  Specialized management of the crops has discouraged the use of much conservation potential but the authors suggest cover crops for sequestering carbon.  Wetlands are less than 1% of cropped areas in the US, but have especially high GHG emission rates due to their waterlogged state, which lacks the oxygen needed to decompose organic matter.  Drainage of the organic matter would allow carbon dioxide to be released at a higher rate, but the authors conclude that it is not feasible to consider carbon sequestration in these soils.
Biofuels present an emerging issue for land management.  About 18% of harvested grain in the US was used for ethanol<!–[if supportFields]> XE “ethanol” <![endif]–><!–[if supportFields]><![endif]–> production in 2007, and more than half of harvested corn grain was for animal feed.  Strong interest exists in developing sustainable energies from biofuels, but a number of concerns for environmental problems have risen from intensification of agriculture<!–[if supportFields]>XE “agriculture” <![endif]–><!–[if supportFields]><![endif]–> and may compromise the overall goal of increasing carbon in the ecosystem. Even as new technologies are developed, it is important for agriculture to continue developing successful soil carbon sequestration<!–[if supportFields]>XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–> practices. 
Very few experiments have addressed best management practices for improving soil carbon storage, and little research has assessed how different practices may affect carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–>.  Morgan et al. suggest the need for low-cost carbon and non-carbon dioxide greenhouse gas information on multiple levels.  Measurements of GHG fluxes<!–[if supportFields]> XE “flux” <![endif]–><!–[if supportFields]><![endif]–> can be used to evaluate the effects of management opportunities and changes in climate on carbon balance, and could be used to estimate large-scale carbon budgets.  Development of a national database is needed to make further assessments.  The authors recommend direct sampling of soil carbon as a more feasible technique for gathering data, rather than expensive and complicated GHG measurement technology.

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