Paul, Eldor A., authorWright, S., authorCollins, H. P., authorHaile-Mariam, S., authorSoil Science Society of America, publisher2007-01-032007-01-032008-03Haile-Mariam, S., H. P. Collins, S. Wright and E. A. Paul, Fractionation and Long-Term Laboratory Incubation to Measure Soil Organic Matter Dynamics. Soil Science Society of America Journal 72, no. 2 (March-April 2008): 370-378. https://dx.doi.org/10.2136/sssaj2007.0126.http://hdl.handle.net/10217/85523Soil organic matter (SOM) in agricultural soils comprises a significant part of the global terrestrial C pool. It has often been characterized by utilizing a combination of chemical dispersion of the soil followed by physical separation. We fractionated soil samples under continuous corn (Zea mays L.) rotations at four long-term sites in the Corn Belt to determine the concentration of C and N associated with soil fractions (light fraction [LF], particulate organic matter [POM], silt size, clay size, and Bradford reactive soil protein [BRSP]) and to identify the change in C concentration and δ13C signal of each fraction using laboratory incubations. Light fractions comprised 3 to 5% of the soil organic carbon (SOC), with no significant difference between conventional tillage (CT) and no-till (NT) treatments. The POM fraction accounted for 5 to 11% of the SOC in the soils with >30% clay and 17 to 23% for the soils with <20% clay. The clay-size fraction contained the highest proportion of SOC. Measurement of 13C during long-term incubation showed that the average mean residence time (MRT) of corn-derived C in the LF was 3.5 yr, whereas the POM fractions ranged from 6 to 12 yr. The 13C changes during incubation show that both fractions consist of a mixture of active and resistant materials, with movement between fractions. The BRSP has long MRTs except in the NT Hoytville soil. Measurement of the dyna mics of these fractions provides a basis for C models to test the impacts of land use and management on C sequestration.born digitalarticleseng©2008 Soil Science Society of America.Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.CO2soil Csoil NSOMglobal terrestrial C and N poolsTexthttps://dx.doi.org/10.2136/sssaj2007.0126