Quantity and spatial variability of soil carbon in the conterminous United States

Abstract

We estimated the soil organic carbon (SOC) and soil inorganic carbon (SIC) inventory for the conterminous USA using the State Soil Geographic Database (STATSGO). The relative contribution of each soil order and Land Resource Region (LRR) to the national SOC and SIC inventory was determined. There are 302 to 1499 ×108 Mg of SOC and 226 to 937 × 108 Mg of SIC in the upper 2 m of soil in the conterminous USA. About 30 and 80% of the upper 2-m SOC is in the 0- to 0.20- and 0- to 1.0-m soil layers, respectively. For SIC, only about 8% of the upper 2-m SIC is in the upper 0.2 m, and about 50% is in the top 1.0-m layer. The relative spatial variability of SOC increases dramatically as soil depth increases while the largest relative variability of SIC is in the surface layer. Because of its large area (27% of the soil area in the conterminous USA), Mollisols are the largest contributors both to the SOC stock (about 31 to 39%) and to the SIC stock (about 43 to 44%) in the conterminous USA. The results of this study provide a view of soil C partitioning by taxonomic group and land resource area, information that may be useful for assessing the impact of land use and climatic change on SOC and SIC pools. © Soil Science Society of America.