Hello，
My current job is to study soil aggregates and soil microorganisms. I want to extract DNA from individual aggregates and measure some soil physical and chemical properties, such as soil carbon and nitrogen. Our aggregates range in mass from 100 to 300 mg, but DNA extraction takes up a large part of its quality. I want to know what methods can be used to measure soil carbon and nitrogen with small-mass soil samples in individual aggregates.
Thank you in advance.
Mengying
@ Mengying, I think even for small mass you may opt wet oxidation method for C estimation and kjldahal method or alkaline permanganate method for N analysis.
The determination of soil organic carbon is based on the Walkley-Black chromic acid wet oxidation method. Oxidisable matter in the soil is oxidised by 1 N K2Cr2O7 solution. The reaction is assisted by the heat generated when two volumes of H2SO4 are mixed with one volume of the dichromate. The remaining dichromate is titrated with ferrous sulphate. The titre is inversely related to the amount of C present in the soil sample.
The Kjeldahl method permits the available nitrogen to be precisely determined in the plant and in the soil. The method of determination involves three successive phases which are, Digestion of the organic material to convert nitrogen into HNO3. Volumetric analysis of the Ammonia formed during the digestion process.
https://vlab.amrita.edu/?sub=2&brch=294&sim=1551&cnt=1
I also support to Mr Prem Baboo and Mr J.C.Tarafdar in this aspect. Otherwise, It could be done by using C- N Analyser if available.
In addition to the above-mentioned relevant and useful suggestions, I would like to mention that its better to opt for either TOC/DOC analyser or C-N analyser since the traditional mohr salt method fails to determine the recalcitrant carbon, especially in samples with high humus.
hi Mengying Ni ,
I think you should use a dry combustion method, with an element analyser (like Tru Spec or Perkin Elmer) because those require just few quantities of soil (0.25 g in Tru Spec or 4 mg in P. E.).
Carbon nitrogen analyser is best for small quantity of samples. It requires a few mg of samples. It is also regarded as reference method for C and N determination.
Thank you for all answers to this question, I will seriously consider it! Thank you all.
Measuring carbon and nitrogen in soil fraction can be done by using standard specification equipment such as JAS-373 Total combustion Analyzer after the separation of sand, silt and clay into aggregates fractions.
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