Estimation of microbial biomass based on water-extractable organic matter from air-dried soils from Japanese forests and pasture

Nagano, Hirohiko*; Kanda, Yuki*; Suzuki, Yuri*; Hiradate, Shuntaro*; Koarashi, Jun   ; Atarashi-Andoh, Mariko  ; Guo, Z.*

Water-extractable organic matter (WEOM) obtained from air-dried soil samples can be used to estimate microbial biomass instead of chloroform fumigation extraction (CFE) using fresh, moist soils and toxic solvents. However, the accuracy of such WEOM-based estimates has not been evaluated. We evaluated relationships between WEOM measurements obtained from air-dried soils and microbial biomass measurements obtained through CFE based on 50 soil samples from each of 10 soil profiles in Japanese forests and pasture. The amount of water-extractable organic carbon (C) obtained from air-dried soils corresponded to 31% of microbial biomass C, demonstrating a strong correlation. This result supports our hypothesis that WEOM represents a quantitative alternative to microbial biomass, particularly for C, offering a solution to the practical difficulties involved in measuring microbial biomass using CFE.