Arginine ammonification as a method to estimate soil microbial biomass and microbial community structure

Ammonium and nitrate production were measured at 2 h following addition of arginine solution (0.3 mg g−1 soil) to 13 unamended soils. The amounts of NH4–N, NO3–N and total inorganic N (i.e. NH4–N+NO3–N) produced were closely related to soil ATP content, biomass C measured by the fumigation–extraction method (FE) and CO2 evolution measured by substrate-induced respiration (r=0.83 to 0.91). The method is little, if at all, improved if both NH4–N and NO3–N are measured in the soil extracts rather than NH4–N alone. Arginine mineralization appears to be a fast and rapid method for estimating soil microbial biomass. However, the method is invalid in acid soil and soils containing large amounts of readily decomposable substrates. Arginine mineralization was not selectively inhibited by cycloheximide and streptomycin so it is not possible to use this approach to estimate separately the fungal and bacterial biomass.