Soil microbial biomass C (Cmic) was estimated by extracting 30-
g oven-dry equivalents of field-moist mineral soil samples in
0.5 M K2SO4 (1:4 w/v) by the chloroform-fumigation-extraction
method described by Brookes et al. (1985) and Vance et al. (1987).
Cmic was calculated from the difference in extractable organic C
between fumigated and unfumigated soil samples as follows:
biomass C = 2.64 EC, where EC refers to the difference in extractable
organic C between the fumigated and unfumigated treatments;
2.64 is the proportionality factor for biomass C released by
fumigation extraction (Vance et al., 1987