Leavitt, S. W., authorFollett, R. F., authorPaul, E. A., authorArizona Board of Regents (University of Arizona), publisher2007-01-032007-01-031996Leavitt, S. W., R. F. Follett, and E. A. Paul, Estimation of Slow- and Fast-Cycling Soil Organic Carbon Pools from 6N HCl Hydrolysis. Radiocarbon 38, no. 2 (1996): 231-239. httpss://journals.uair.arizona.edu/index.php/radiocarbon/article/view/1903/1904.http://hdl.handle.net/10217/81278Publisher version: https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/1903/1904.Acid hydrolysis is used to fractionate the soil organic carbon pool into relatively slow- and fast-cycling compartments on soils from Arizona, the Great Plains states and Michigan collected for carbon isotope tracer studies related to soil carbon sequestration, for studies of shifts in C3/C4 vegetation, and for "pre-bomb" soil-carbon inventories. Prior to hydrolysis, soil samples are first treated with cold 0.5-1N HCl to remove soil carbonates if necessary. Samples are then dispersed in a concentrated NaCI solution (p~1.2 g cm-3) and floated plant fragments are skimmed off the surface. After rinsing and drying, all remaining recognizable plant fragments are picked from the soil under 20x magnification. Plant-free soils, and hot, 6NHCl acid-hydrolysis residue and hydrolyzate fractions are analyzed for carbon content, δ 13C and 14C age, and the carbon distribution is verified within 1-2% by stable-carbon isotope mass balance. On average, the recalcitrant residue fraction is 1800 year older and 2.6‰ more 13C-depleted than total soil organic carbon. A test of hydrolysis with fresh plant fragments produced as much as 71-76% in the acid-hydrolysis residue pool. Thus, if plant fragments are not largely removed prior to hydrolysis, the residue fraction may date much younger than it actually is.born digitalarticlesengsoil dynamicscarbon cyclingsoil carbon poolsTextThis article is open access and distributed under the terms and conditions of the Creative Commons Attribution 3.0 Unported (CC BY 3.0).