I applied the method on different samples with organic content. Sometimes the samples without fumigation treatment showed a higher N-content than the fumigated samples. I think that this could only be the case if either N was lost during chloroform fumigation via NH3-volatilization or N-immobilization. Are there possible explanations available, or does anybody have different suggestions? We tested a run varying the water content of certain samples; this did not show any influence on the outcome.
Hello Christian:
Unless the soils were significantly alkaline, loss as NH3(g) is not likely to be an important avenue for loss. A more likely occurrence is that lysed cell materials were then immobilized in the soil solid phase. I believe this has been reported for soils with significant organic matter content, but I don't have the citation at the ready. Hope this helps. -Bryan
The duration of fumigation was 24 h. Yes, Ctot was measured and looked rather plausible, at least the values from the fumigated samples were higher. The TN was measured as NPOC.And our organic matter content was not that high (~5-10 %DW TOC).
sorry, NPOC was of course for carbon. It was basically a standard TN analysis with a TOC/TN analyzer. These samples were landfilled waste material, but already with soil or leaf litter samples similar observations occured or at least I heard of them. The sample manipulation was very similar (non-fumigated extraction 24 h before).
With the waste material it could also have been possible, that chloroform reacted with some waste compounds (e.g. plastics,..). But I never read anything about this observation (neither for soil, nor for waste material).
1 M KCl and blind solution was fine. Yes, the samples were filtered with an ash-free filter. Analyzing the filter residue would have been a very good idea. Next time though, since of course it was disposed of. Thank you very much.
Well, it looks like you have some good avenues for investigation… I would also add that since this is the fumigation/ extraction technique, much of the N will be in a soluble organic form, and that strong molar solutions often impeed bringing dissolved organic nitrogen into solution… I was in the habit of extraction with the salt solution, followed by one of DI water… The water extract, despite coming after the salt solution was always tinted, suggesting better recovery of organics. Recall that the salt solution is designed to capture DIN.
For mass balance, if possible, trap the gazeous effluent in an acidic soultion (bubbling train). All NH3(g) will be convert in NH4 in this acidic solution. Then after the fumigation measure N.NH4 in this solution.
Yann
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