The most serious criticism of the CFE method is directed towards the way the quantity of material solubilized by chloroform is related to the size of the original biomass, i.e. the set values of kEC; kEN and kEP (Jenkinson et al., 2004). The values being used are derived from measurements made on a small selection of organisms added to soil and fumigated. These organisms, grown on nutrient-rich media, may not be good models for starving and diverse soil population (Jenkinson et al., 2004). Some researchers measured kEC by a different method. A soluble 14C-labelled substrate such as glucose is added to soil, allowed to decompose for a day or two, and fumigated. The 14C rendered extractable by fumigation, expressed as a fraction of the insoluble 14C remaining in the soil at the time of fumigation, gives kEC (Dictor et al., 1998). The difficulty was in the assumption that all of the insoluble 14C is present as live microbial biomass, with none stabilized in non-living structures such as insoluble polysaccharide gums, making the values of kEC obtained too small. There are similarities between the biomass in different soils. This implies that the values of kEC; kEN or kEP can be applied to different aerobic surface soils without major error (Jenkinson et al., 2004). Joergensen et al. (2011) found The kEC value of 0.45 to convert extracted organic C to biomass C is still valid. There is a need to review of the kEC; kEN and kEP: In the meanwhile we use 0.45 for kEC; 0.45 for kEN and 0.40 for kEP: Better analytical methods are now available for measuring extractable C and N.
Dictor M-C, Tessier L, Soulas G 1998: Reassessement of the Kec coefficient of the fumigation–extraction method in a soil profile. Soil Biol. Biochem., 30, 119–127. http://linkinghub.elsevier.com/retrieve/pii/S0038071797001119.
Jenkinson DS, Brookes PC, Powlson DS 2004: Measuring soil microbial biomass. Soil Biol. Biochem., 36, 5–7.
Joergensen RG, Wu J, Brookes PC 2011: Measuring soil microbial biomass using an automated procedure. Soil Biol. Biochem., 43, 873–876. http://dx.doi.org/10.1016/j.soilbio.2010.09.024.
In the case of extraction of organics from a solid it is important to understand the partitioning of the organics between the sample and the solvent. In the case of soils from different regions and of different pH and composition and particle size distributions, the degree of extraction of extract organics of different types will vary. Depending upon the types of organics that you are hoping to measure chloroform will provide different efficiencies of extraction. There is no simple answer here. This has a lot to do with adsorption of the organics on the surface of the base soil particles, absorption into insoluble phases not to mention the geometry of the particles and pore structure. The extraction efficiency will be significantly impacted by the kinetics of the adsorption and desorption processes for bot chemisorption and physisorption. Perhaps doing a study of the standard methods versus the chloroform method may provide some insight. In this case, it would probably be necessary to evaluate the efficiencies for different classes of organics as well as these will likely vary between classes.
Please look at the following below links which may help you in your analysis:
http://allison.bio.uci.edu/protocols/microbiabiomasscn.pdf
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.475.3836&rep=rep1&type=pdf
Thanks
- Badges
- Science topic