ORIGINAL PAPER Chemical stabilization of organic carbon pools in particle size fractions in no-till and meadow soils K. Lorenz & R. Lal & M. J. Shipitalo Received: 20 November 2007 / Revised: 16 April 2008 / Accepted: 25 April 2008 / Published online: 27 May 2008 # Springer-Verlag 2008 Abstract The knowledge about the relevance of physical and chemical fractionation methods to soil organic carbon (SOC) stabilization mechanisms is fragmentary but needed to manage the SOC pool. Therefore, our objective was to compare the C contents of the particle size fractions coarse and fine sand, silt, and clay of the two uppermost horizons of a soil under three different management systems (meadow; no-till corn, NT; no-till corn with manure, NTm). The mineral composition was dominated by silt (48–60%). However, coarse sand and clay showed the highest enrichment of C compared to the bulk soil. In spite of an enrichment factor below 1, the high proportion of silt made this fraction the main C store. In the upper 30 cm, this fraction amounted to 27.1 Mg C ha -1 in NTm and progressively less in NT (15.5 Mg C ha -1 ), and meadow (14.9 Mg C ha -1 ), representing 44%, 39%, and 39% of the total SOC pool, respectively. The C in the isolated particle size fractions was further investigated by an oxidizing treatment with Na 2 S 2 O 8 and a treatment with HF to solubilize the mineral phases. The pools of oxidizable C were comparable among particle size fractions and pedons, as indicated by Na 2 S 2 O 8 treatment. The pools of C preferentially associated with soil minerals were also comparable among pedons, as indicated by HF treatment. However, NTm stored the largest pool (12.6 Mg ha -1 ) of mineral-associated C in 0–30 cm depth. The silt-associated and mineral-bound SOC pool in NTm was greater compared to NT due to increased organic matter (OM) input. Thus, the silt particle size fraction at the North Appalachian Experimental Watershed (NAEW) has the potential for SOC sequestration by stabilizing OM inputs. Mineralogical and molecular level analyses on a larger set of fractions obtained from entire rooted soil profiles are required, however, to compare the SOC sequestration capacity of the land uses. Keywords Carbon sequestration . Land use and soil management . Hydrofluoric acid . Disodium peroxodisulfate . Combined particle size and chemical fractionation Introduction The soil organic carbon (SOC) pool is strongly affected by land use changes and agricultural practices and is derived from surface input of plant debris but mainly from roots and associated turnover of mycorrhizal hyphae (Lal 2004; Rees et al. 2005; Godbold et al. 2006). Conversions from forest or crop to pasture may increase the SOC pool, whereas conversion of forest to arable land probably results in a depletion of the SOC pool. The surface soil is usually more active in sequestering C after land use change than deeper soil horizons (Guo and Gifford 2002). The SOC concentrations in mineral soils, however, may take decades to centuries to equilibrate after a change in land use or management (Leifeld and Kögel-Knabner 2005). Thus, at early stages of anthropogenic perturbations, assessment of changes in sensitive SOC fractions may be useful in Biol Fertil Soils (2008) 44:1043–1051 DOI 10.1007/s00374-008-0300-8 K. Lorenz (*) : R. Lal Carbon Management and Sequestration Center, School of Environment and Natural Resources, The Ohio State University, 2021 Coffey Road, Columbus, OH 43210-1085, USA e-mail: lorenz.59@osu.edu M. J. Shipitalo USDA-ARS, North Appalachian Experimental Watershed, P.O. Box 488, Coshocton, OH 43812-0488, USA