NINHYDRIN-REACTIVE-N RELEASED BY THE FUMIGATION-EXTRACTION METHOD AS A MEASURE OF MICROBIAL BIOMASS UNDER FIELD CONDITIONS

Ninhydrin-reactive N extracted after a 1-day fumigation with CHCl3 was compared to the C and N released by the fumigation-incubation method (FIM) in 37 soil samples (0-5 cm depth) collected from three tillage systems, and pastures in Atlantic Canada. The soils were slightly acidic, fine sandy loam Podzols with a relatively wide range of organic C and low clay content. Biomass C and the mineral N flush obtained using the FIM were closely related (r = 0.98) in all soils. Ninhydrin-reactive N was positively correlated with both biomass C (r = 0.88) and the mineral N flush (r = 0.92). Measurements of ninhydrin-reactive N released in the fumigation-extraction method provided a rapid assay for estimating microbial biomass C and N, and a comparison of microbial N content between different soils in field studies. For the tillage systems, where ninhydrin-reactive N ranged from 2 to 20-mu-g N g- soil, multiplying the extracted ninhydrin-reactive N by 24 and 2.8 provided an estimate of microbial biomass C and the mineral N flush, respectively.