Hi,

forget about a 3-component mixing model.
Re-analyse your samples after proper removal of the carbonate.
Good luck, Michael

> Folks,
>
> I am characterizing particulate plant derived organic matter input to
> the soil.  The approach I have taken is planting C3 plants into a
> soil with a long C4 history.  The particulate organic matter in the
> soil at the start of the experiment had a del vPDB signature of
> -14.000 and the new C3 input has a del vPDB of -28.000.  My problem
> is that the protocol for isolating the organic matter requires that I
> co-collect the organic matter with the sand fraction of the soil,
> which contains about 18% carbonate with a del vPDB of 0. I'm
> wondering if anybody can help me with a three source mixing model
> that can be run using only one isotope?  Using a separate analysis of
> the soil I can calculate the amount of carbonate in each sample but I
> need to determine the proportion of each plant source (C3 or C4) in
> the remaining organic carbon.
> Ideally I would have removed the carbonate prior to isotopic analysis
> but at the time of sample prep I didn't realize how much of an issue
> the carbonate would be.
>
> Thanks
> jude
>
> --
> ####################
> Jude Maul
> Department of Horticulture
> Cornell University
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> (607)255-0883 (office)
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>