We are trying to measure microbial C,N and P from rather small soil samples. We reviewed several methods based on chloroform fumigation. However, the methods to flush the C, N and P are using different solutions (typically KSO4 for C & N and NaHCO2 for P). Are there any methods that allow washing of all three elements from the soil using the same solution for flushing the soil?
Hello Frank,
Nitrate is readily displaced by anions such as sulfate from most soils and a considerable concentration of K is require to displace the NH4, so these requirements must be met. In addition, ions such as F efficiently displace phosphate from its surface complexes with the hydrous oxides of Fe and Al. (Look up the method of Bray and Kurtz, 1945.) Consequently I see no reason that an acidic solution of K2SO4, also containing NH4F, should not effectively displace all three of the species you are interested in.
Regards, Paul.
Frank, If the soil is in the alkaline range, a separate extraction for P is suggested and F may not replace P from the soil complex. Thus, two different extractions may be needed. It may work if the soil is in the acidic range as Paul suggests.
Best, Blaise
Thanks for the excellent answers. I indeed work with acidic soils that have a high organic matter content (organic layers and some horizons are rich in Fe). The other question that comes into my mind is why I should not use the NaHCO2 to extract microbial C and N (in addition to the P). The C is detected with a DOC analyser and anyway the HCO3+ will equilibrate with atmospheric CO2 during processing.
I am just wondering since all publications I reviewed went through a double extraction process.
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