PARENT SESSION
Symposium #5: Sustaining and restoring our soil.
Sponsored by ESA Soil Ecology Section
Organized by: S.M. Adl. and S. Morris.
Monday, August 6, 2001. 1:00 PM to 4:50 PM. Madison Ballroom A

Changes in soil carbon stocks with land management and increasing atmospheric CO₂.

Schlesinger, William¹, ¹

ABSTRACT- Much attention has focused on the potential for carbon sinks to mediate the rise of CO₂ in Earth's atmosphere and to help the United States achieve its first commitment to the Kyoto Protocol. In agricultural lands, a sink for atmospheric carbon (i.e., CO₂) in soils may derive from the application of conservation tillage and the regrowth of native vegetation on abandoned agricultural land. Intensification of agricultural management may also increase soil carbon stocks, but the greater accumulation of soil organic matter in fertilized fields carries a carbon "cost" in the form of CO ₂ emissions during the production and application of inorganic fertilizer. Similarly, soil carbon accumulations in irrigated semiarid lands must be discounted by CO₂ that is emitted when energy is used to pump irrigation water and when CaCO ₃ precipitates in the soil profile. A sink for carbon in soils is also postulated to result from plant growth at high CO₂; however, in a Free-Air CO₂ Enrichment (FACE) experiment in North Carolina, higher %C in the 0-15 cm soil layer in fumigated plots (+200 ppm CO ₂) of a pine forest is not associated with significant net C sequestration in soils after 3 years. The mass of carbon in the forest floor has increased significantly in fumigated plots, but wood growth remains the only major sink for carbon in the forest. These disparate studies suggest that soils are not likely to serve a major role as a carbon sink, and perhaps may become a significant additional source of atmospheric CO₂ with global warming.

KEY WORDS: Soil Organic Matter, Carbon Sequestration, Free-Air CO2 Enrichment