Soil Carbon StoCkS in the U.S.: CUrrent Data anD FUtUre inventorieS

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 the soil by changing land uses and/or management systems. The objectives of this paper are 1) to report total U.S. C stocks derived from existing soil survey and land cover data, 2) estimate potential increases in soil C that could be achieved with changes in land cover and agricultural management, and 3) to outline current efforts to improve soil survey estimates of U.S. soil C stocks through a scientifically-based and statistically valid inventory. The soil survey for non-federal lands in the U.S. at scales of 1:12,000 to 1:24:000 is essentially complete and is available as the Soil Survey Geographic database (SSURGO). In addition to the spatial database, SSURGO includes soil attribute data, including organic C, CaCO 3 equivalent, bulk density, and fragment content, for layers of components of each map unit. The second phase of the NRCS effort to evaluate U.S. carbon stocks will be measurement of soil C and related data major land uses and agricultural management systems within soil groups expected to have similar C dynamics. For this inventory, soils will be sampled to 1 m at about 30,000 points at 6,000 locations. At each sample point, the soil will be described, and for each horizon, bulk density will be measured by appropriate techniques and total C and CaCO 3 equivalent will be estimated from Visible and Near Infra-Red spectra. The goal of this phase is to collect scientifically defensible and statistically valid data for soil C stocks that can be used to guide policy decisions and conservation planning for the nation.