The amount of C stored in soil in terrestrial ecosystems depends on the balance between C inputs (through plant residues) and the decomposition of soil C. Sequestration of atmospheric C in soil requires increasing plant C inputs, reducing decomposition or both. Both C inputs and SOM decomposition (and thus soil C levels) may be influenced by management. The degree to which management can effect C stocks, however, is highly dependent on the previous landuse history. For example, if native grasslands with high initial C stocks are brought into livestock production with good management, there may be relatively little potential to increase soil C. Conversely, systems in which soil C has been depleted due to poor management can have a high capacity to store additional C upon implementation of improved management. For example, cultivation and conversion of native soils to annual crop agriculture generally causes a substantial loss of the original soil C stock (typically 20-50%). Thus, pastures that have been established on soils degraded from previous cultivation should have a high potential to rebuild soil and biomass C stocks, if management changes that enhance productivity are introduced. Numerous studies show significant rates of C accrual of 0.5-1 Mg per ha per year for cultivated land reverted to grassland, for periods of up to several decades.
The purpose of this project is to create a knowledge base for reliably estimating the potential for C sequestration through the adoption of improved pasture and livestock management systems in the southeastern US. An integrated systems approach combining collection and analysis of comparative soil samples, establishment of monitoring plots, and extant landuse databases will be used. This information, when combined with GIS technology and other ongoing work within our program, will be used to calibrate and drive the Century ecosystem/soil C model for aggregating soil C levels and changes -- spatially -- to state, regional and national levels.