A key component for sustaining production in grassland ecosystems is the maintenance of soil organic matter (SOM), which can be strongly influenced by management. Many management techniques intended to increase forage production may increase SOM, thus sequestering atmospheric C. Likewise, SOM losses can potentially be reversed, and atmospheric C sequestered, with adoption of improved range management practices. Further, conversion from either cultivation or native vegetation into managed grassland could also sequester atmospheric C. Assessing C sequestration rates requires (1) information about past and current land use/management practices and (2) the means to translate range management information into estimates of CO2 fluxes. We have developed such as system within the central North American Great Plains using a mechanistic biogeochemical model driven by remotely sensed data. Our system consists of a production efficiency model that estimates plant CO2 uptake and is linked to a SOM model derived from the Century model. The production efficiency model is driven by frequently available moderate resolution (MODIS) satellite data. The plant primary production sub-model dynamically allocates C to above- and belowground structures based upon foliage removal rates by grazers and plant water and nutrient demand. Field-level model validation in the US will be completed during the 2004 growing season and region-wide assessments will then be carried out. The global availability of MODIS data coupled with our model-based approach ensures that US results are applicable to other semiarid regions. We discuss how integrated assessments in East Africa inform grassland managers, and potential applications in the Sudan-Sahelian region.