Elevated carbon dioxide does not offset loss of soil carbon from a corn-soybean agroecosystem.

The potential for storing additional C in U.S. Corn Belt soils - to offset rising atmospheric [CO(2)] - is large. Long-term cultivation has depleted substantial soil organic matter (SOM) stocks that once existed in the region's native ecosystems. In central Illinois, free-air CO(2) enrichment technology was used to investigate the effects of elevated [CO(2)] on SOM pools in a conservation tilled corn-soybean rotation. After 5 and 6 y of CO(2) enrichment, we investigated the distribution of C and N among soil fractions with varying ability to protect SOM from rapid decomposition. None of the isolated C or N pools, or bulk-soil C or N, was affected by CO(2) treatment. However, the site has lost soil C and N, largely from unprotected pools, regardless of CO(2) treatment since the experiment began. These findings suggest management practices have affected soil C and N stocks and dynamics more than the increased inputs from CO(2)-stimulated photosynthesis. 2009 Elsevier Ltd. All rights reserved.