Grasslands contain 12% of the earth's soil organic matter and temperate grasslands averages 192 Mg C ha-1. Historical C losses, due to intensive use of grasslands, have resulted in the transfer of substantial amounts of C to the atmosphere. Maintaining historically degraded areas under well-managed permanent grassland constitutes a potential C sink. Even within well-established pastures, soil C can increase by eliminating soil disturbance and increasing primary production. Since soil C content is determined by the balance between inputs and outputs, it seems that increased production should uniformly lead to increased soil C if outputs remain unchanged. But, is this always the case? Conversely, decreased production seems likely to result in decreased soil C, yet soil C can increase even in areas overgrazed to the extent that production has decreased. What factors affect how changes in inputs affect soil C? How widespread are instances where increased inputs don't result in increased soil C? In order to address these questions, literature data was compiled for various types of management improvements - fertilizing, irrigating, sowing improved species, and improving grazing management - that may lead to soil C responses inversely related to changes in productivity. We parameterized the Century model with data from these studies. Model output was integrated with spatial distributions of various management practices, species composition, soil characteristics, and climate to identify regions that can potentially sequester large amounts of atmospheric C, and those likely to lose C, following implementation of management practices intended to increase production.