Continuous measurements of carbon flux from 1997 to 2002 by eddy-covariance were used to evaluate the carbon budget for a maize (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation agricultural ecosystem that has been in no-till cultivation for over 14 years. These measurements were used to determine the net ecosystem exchange of carbon (NEE) at the local scale and for the North Central Region of the U.S. (NCR). Results show that at the local scale, the no-till ecosystem is a carbon sink when planted with maize (576 g C m−2 per year) and soybean (33 g C m−2 per year). On a regional scale, the carbon sink is proportionally lower than that of the local scale. This is attributed to regional consumption of the grain (over 85% of all NCR grain is consumed elsewhere in the world) combined with the carbon emissions associated with agricultural practices. Since nearly 100% of both maize and soybean yields are consumed annually, e.g. all carbon stored in grain is consumed somewhere in the world, the long-term carbon-sequestration potential of this system is lower than revealed with the local and regional analysis. Accounting for 100% grain consumption, maize still acts as a C-sink of 184 g C m−2 per year while soybean becomes a C-source of 94 g C m−2 per year. As these two crops are grown in rotation, the system when accounting for all emissions to the atmosphere is a net sink of 90 g C m−2 per year. Overall, however, the potential exists for long-term carbon sequestration.
