This part of ISO 14240 specifies a method for the estimation of microbial biomass of soils by measurement of total extractable organic biomass material mainly from freshly killed microorganisms. The method is also applicable to the estimation of microbial nitrogen and microbial ninhydrin-reactive nitrogen in soil, but this part of ISO 14240 describes only the measurement of extractable organic carbon. The fumigation-extraction (FE) method is applicable to aerobic and anaerobic (water-logged, paddy) soils over the whole range of soil pH. Biomass can be also measured in soils containing actively decomposing substrates and soils supersaturated with potassium sulfate solution.