This description is modified from CASMGS's central website.

Both in the United States and internationally, concern is mounting about the rapid buildup of atmospheric carbon dioxide (CO2) and other greenhouse gases and the implications for our climate and environment (U.S. Climate Action Report 2002). Agriculture can help mitigate these problems in a cost-effective and environmentally sound way. 

Through the use of a variety of improved farming practices, soil carbon stocks can be increased, thereby sequestering carbon that would otherwise be present in the atmosphere as CO2. At the same time, increasing the organic matter content of our agricultural soils would be of enormous benefit for improving the quality and sustainability of our agricultural production systems. Higher organic matter content is directly tied to soil fertility and crop production capacity. The former Chief of USDA's Natural Resource Conservation Service, William Richards, estimates that a percentage point increase in soil organic matter content (e.g., going from 2% to 3% organic matter) translates into a $250/acre increase in the value of Ohio farmland. Conservation farming practices and increased soil organic matter provide other collateral benefits by reducing soil erosion and improving water quality.

How does the increase in atmospheric CO2 relate to the terrestrial carbon cycle and agriculture?

The carbon cycle - the continual recycling of carbon between the atmosphere, plants, animals and soil - is the basis of all terrestrial life. Plants convert carbon dioxide (CO2) into tissue through photosynthesis, forming the first link in the food chain. Upon their death, plant tissues are decomposed by soil microorganisms, and the carbon in the biomass is eventually released back to the atmosphere as CO2 through respiration. However, the decay of organic materials is slowed by a number of factors resulting in the formation of organic residues (often referred to as humus) which can persist in the soil for hundreds, or even thousands, of years. Consequently, soils contain the largest reservoir of carbon in the terrestrial biosphere - about twice that present in all terrestrial vegetation. U.S. agricultural soils typically contain from 1% to 5% of their total weight as organic carbon.

At present, the amount of CO2 in the air is increasing exponentially, by over 3 billion tons of carbon per year, primarily from the combustion of fossil fuels for energy and transportation. Other sources of this buildup of CO2 include deforestation and biomass burning, mainly in the tropics. Historically, U.S. agricultural soils have also been a source of CO2. With settlement and the expansion of agriculture, forests were cleared, wetlands were drained and almost all of the tallgrass and midgrass prairies were plowed. These activities resulted in the release of large amounts of CO2 from soils, due to the increased oxidation of soil organic matter caused by drainage and intensive tillage. Crop yields were low and crop residues were often removed from the fields, reducing the replenishment of organic matter (carbon) to soil. As a result, the carbon contents of most agricultural soils were reduced by 30-50% or more from their original levels. However, in recent decades, higher yields, greater crop residue return and the use of less intensive tillage practices have shown promise for reversing this trend. In addition, many marginal croplands have reverted to forests and grasslands, some as the result of government programs such as the Conservation Reserve Program and the Wetlands Reserve Program. Consequently, agricultural soils now represent a large potential "sink" for CO2, which can be exploited to sequester carbon through the increased use of conservation farming practices.