Growing plants take carbon dioxide from the air and store it as carbon in their tissues. Most of this carbon is returned to the atmosphere as carbon dioxide when crops are harvested and consumed. Some carbon, however, can be permanently stored, or sequestered, in the soil as organic matter. Changes in land management can potentially increase the accumulation of organic carbon in soil.
The amount of carbon stored in soils also depends on how the climate changes and how much carbon dioxide is in the atmosphere, say researchers from the University of Illinois at Urbana-Champaign and Oak Ridge National Laboratory in Tennessee.
"Our research focuses on the feasibility of different sequestration schemes for reducing natural emissions of carbon dioxide or enhancing the natural uptake of atmospheric carbon dioxide," said Atul Jain, a U. of I. professor of atmospheric sciences and lead author of a paper published in the Oct. 12 issue of Geophysical Research Letters. "Converting from conventional plow tillage to no-till practice is among the most cost-effective ways to reduce the buildup of carbon dioxide in the atmosphere."
To study the effect of changes in climate and atmospheric carbon dioxide on soil carbon sequestration, the researchers used a new Earth-system model called the Integrated Science Assessment Model. Developed by Jain and his graduate students, the model includes the complex physical and chemical interactions among carbon-dioxide emissions, climate change, carbon-dioxide uptake by plants and oceans, and changes in farming practices.
About 18 percent of cropland in the United States and about 30 percent of cropland in Canada is under no-till, Jain said. By not tilling their fields, farmers can save labor and fuel costs, reduce soil erosion and preserve precious nutrients. No-till also increases the accumulation of soil organic carbon, thereby resulting in sequestration of atmospheric carbon dioxide.
Changes in no-till land management were simulated with and without changes in climate and carbon dioxide levels over the period 1981 to 2000. All model simulations were based upon the actual adoption of no-till practices on U.S. and Canadian farms.
"Comparing the model results with and without changes in carbon dioxide and climate allows us to estimate the impact of recent changes in climate and carbon dioxide on soil carbon sequestration," Jain said. "Over the period 1981 to 2000, 868 million tons of carbon were stored in solids under no-till farming. Five percent of this carbon storage comes about because climate change and increasing atmospheric carbon dioxide accelerate carbon storage in soil. Future increases in no-till could sequester enough carbon to satisfy nearly one-fifth of the total U.S. reduction in carbon-dioxide emissions called for by the Kyoto Protocol."
The effects of climate change on carbon storage will vary from place to place because of differences in how soil moisture and soil temperature change as the climate warms, Jain said. In general, in central and western Canada, the eastern United States, and portions of Florida and Texas, carbon sequestration may increase. In other areas, such as Illinois, climate change will reduce the amount of sequestered carbon.
"Climate change will reduce the gains in the carbon storage from no-till in some areas, but there is still a net gain in stored carbon," Jain said. "In the future, farmers could receive credit for the carbon sequestered in their fields under a carbon-trading arrangement such as has been proposed for the Kyoto Protocol."
Co-authors of the paper were Oak Ridge scientists Tristram West and Wilfred Post, and Illinois graduate student Xiaojuan Yang.
The U.S. Department of Energy funded the work.
Editor's note: To reach Atul Jain call 217-333-2128; e-mail: firstname.lastname@example.org.