This procedure compares the amount of total organic carbon (TOC) in a chloroform-fumigated soil sample to that in a nonfumigated soil sample to determine soil microbial biomass. In the chloroform-fumigated sample, TOC will be higher because the sample contains the cell contents of lysed microbial cells. Hence the difference in extracted TOC between fumigated and nonfumigated samples will provide a measure of microbial biomass (Vance et al., 1987). Note that you can only assume that this TOC is of microbial origin if the soil samples have been picked free of roots, litter, earthworms, etc. (the microfaunal contribution to TOC is less than 5%).

Fumigations are carried out for a period of 2 days in vacuum-desiccators with alcohol-free chloroform. Soil samples are extracted with 0.5M K2SO4 and the filtrate is analyzed for TOC. Analysis results need to be adjusted to a TOC/g dry soil value. It is important to refrigerate soil samples until the fumigation and K2SO4 extractions are performed.

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