In this paper we describe the GCTE global Soil Organic Matter Network (SOMNET) before focusing on the European network of long-term sites. We then select two examples from the European site network and demonstrate how such data can be used to (a) track long-term changes in soil organic matter, (b) evaluate and compare soil organic matter models, and (c) make rough estimates of the potential for carbon (C) sequestration in soils at the regional (European) level. Our simple calculations based on only two long-term experiments suggest that amendment of arable soils with 10 Mg ha À1 of organic manure could lead to an increase in current total European soil C stock to 30 cm of about 4.8% over 90 yr, a scenario with limited potential for sequestering C. Similarly, afforestation through natural woodland regeneration of 30% of current arable land (surplus to requirements by 2010) could lead to an increase in current total European soil C stock of 12.4% over 100 yr. This is equivalent to 43 Tg C yr À1 or 3.8% of anthropogenic CO 2 ±C emissions from Europe. If temporary C storage in standing woody biomass is included in the estimate, the amount of C sequestered is quadrupled and could account for 15.28% of Europe's annual CO 2 ±C emissions. This is equivalent to 2.8% of annual global anthropogenic CO 2 ±C emissions. These calculations are presented to demonstrate a simple technique for estimating rough C sequestration potentials but they do suggest some potential to sequester C in European agricultural soils. As a result, a more sophisticated approach using statistical relationships derived from a large number of long-term experiments was developed. The need for balancing the effects of these scenarios on soil C against other environmental considerations is discussed. Methods for improving estimates of the potential for soil C sequestration using the European site network are also discussed.
