U.S. Soil Carbon Stocks Derived From SSURGO and Pedon Data.

There is an urgent need for site and condition specific soil carbon inventories to increase the reliability of estimates of total national stocks and the amount of carbon that can be practically stored in soil by changing land uses and/or management systems. The objectives of this paper are 1) to report spatial distribution of total U.S. C stocks derived from soil survey and land cover data, 2) compare soil C stocks among land covers, and 3) compare Soil Survey Geographic database (SSURGO) estimates with amounts derived from the NCSS Soil Characterization data. The SSURGO database includes soil property data for major horizons to >1 m depth in addition to spatial distribution of soils. Each property for each map unit component includes a representative value (RV) for dominant land cover conditions and high and low values for departures from the dominant condition. Soil C stocks to 1 m were estimated from overlay of National Land Cover Data on SSURGO and, if SSURGO data were not available, STATSGO (State Soil Geographic Database) data. In addition, soil C stocks were calculated from measured soil property data for >1,000 pedons from across the nation. Results from the SSURGO estimates indicate that the U.S. has about 65 Pg of soil organic C to 100 cm depth. Spatial distribution of the C stocks was different from the distribution of surface horizon organic C concentration because of the effects of soil depth, coarse fragments, and bulk density. In general, soil C stocks derived from measured data were greater than SSURGO estimates.