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United States Department of Agriculture

Agricultural Research Service


item Paul, E
item Collins, Harold - Hal
item Leavitt, S

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Information on the mean residence time (MRT) of soil organic matter (SOM) on different soil types and management is required for pedo- geological, agronomic, ecological and global change interpretations. This is best determined by carbon dating the total soil together with acid hydrolysis and carbon dating of the non-hydrolysable residue (NHC). Midwestern US soils in transect from Lamberton, MN to Kutztown, PA were found to contain from 33% to 65% of their SOC in the non-hydrolysable fraction. Soils on lucustrine deposits had the most NHC. Glacial till and shale soils the least. The MRT's of surface horizons of soils ranged from modern to 1100 y with an average of 560 years. Soil age increased to an average of 1700 y in the 25-50 cm depth increment and 2757 y in the 50-100 cm increment. The NHC was 1340 y greater at the surface and 5584 y at depth. The MRT's of the total soil C were inversely correlated to sand and directly related to clay content. Silt did not have a significant effect on the total soil C content and MRT was described by a four parameter model. The complexity of the equation reflected the strong effect of depth where SOC decreases while greatly increasing the MRT. The relationship between the MRT of the SOC with that of NHC is 1338 y older than the total SOC. The MRT of these soils as determined with carbon dating of the naturally occurring 14C was compared to that measured with the 13C signal produced by approximately 30 y of continuous corn (C4) on soil with a known plant history of C3-C4 cropping. The equation of 14C MRT=176(13C MRT)0.54 with an R2 of 0.70 showed that long- term 13C studies correlate well with the total MRT as they are indicative of the dynamics of the active and slow pools and not of the total SOC.

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