Rapid estimation of microbial biomass in grassland soils by ultra-violet absorbance

A reliable and simple technique for estimating soil microbial biomass (SMB) is essential if the role of microbes in many soil processes is to be quant ified. Conventional techniques are notoriously time-consuming and unreprodu cible. A technique was investigated that uses the UV absorbance at 280 nm o f 0.5 M K2SO4 extracts of fumigated and unfumigated soils to estimate the c oncentrations of carbon, nitrogen and phosphorus in the SMB. The procedure is based on the fact that compounds released after chloroform fumigation fr om lysed microbial cells absorb in the near UV region. Using 29 UK permanen t grassland soils, with a wide range of organic matter (2.9-8.0%) and clay contents (22-68%), it was demonstrated that the increase in UV absorbance a t 280 nm after soil fumigation was strongly correlated with the SMB C (r = 0.92), SMB N (r = 0.90) and SMB P (r = 0.89), as determined by conventional methods. The soils contained a wide range of SMB C (412-3412 mug g(-1) dry soil), N (57-346 mug g(-1) dry soil) and P (31-239 mug g(-1) dry soil) con centrations. It was thus confirmed that the UV absorbance technique describ ed was a rapid, simple, precise and relatively inexpensive method of estima ting soil microbial biomass. (C) 2001 Elsevier Science Ltd. All rights rese rved.