Forested plantations have the potential to sequester a significant amount of carbon in soil, and it may be possible to manage plantations to promote C sequestration in soil. However, a better understanding of how management affects soil C pools and processes is needed. We tested the effects of repeated fertilizer applications, competing vegetation control, and the combined effects of each type of treatment on soil carbon quality in ponderosa pine (Pinus ponderosa Dougl. ex Laws. var ponderosa) plantations along a site quality gradient in northern California. We measured the quantity of C in the top 20 cm of mineral soil and attempted to describe the quality of that C by density fractionation and C mineralization potential as determined by long -term incubation. Preliminary results for mineral soil C content and quality in response to these silvicultural treatments are presented.