THE FUMIGATION-EXTRACTION METHOD TO ESTIMATE SOIL MICROBIAL BIOMASS -CALIBRATION OF THE K(EN) VALUE

The k(EN) value (=extractable part of microbial biomass N after fumiga tion) of the fumigation-extraction method was assessed using the C-to- N ratio of the organic matter which was rendered extractable by CHCl3 fumigation. The data for this calibration approach was obtained from 5 1 arable and 23 grassland soils. The second calibration approach was t o compare the relationship between N rendered extractable by CHCl3 fum igation and the C-to-N ratio measured in the flush of the fumigation-i ncubation method by recalculating data obtained from the literature. O n the basis of these two approaches, we recommend using a k(EN) value of 0.54 as originally proposed by Brookes et al. (Soil Biology & Bioch emistry 17, 837-842, 1985).