Relationships of chloroform fumigation-incubation to soil organic matter pools

Microbial biomass is part of the active pool of soil organic matter that pl ays focal roles in decomposition of organic materials, nutrient cycling and biophysical manipulation of soil structure. We compared two commonly used variants of the chloroform fumigation-incubation method in their relationsh ips with other active, passive and total soil C and N pools in soils from T exas, Georgia, Alberta and British Columbia. The relationship of potential C mineralization with chloroform fumigation-incubation without subtraction of a control was much stronger (r(2) = 0.81 +/- 0.10 among five data sets w ith a total of 844 observations) than with subtraction of a control (r(2) = 0.30 +/- 0.22). Similarly, the relationship of soil organic C with chlorof orm fumigation-incubation without subtraction of a control was better (r(2) = 0.80 +/- 0.13) than with subtraction of a control (r(2) = 0.38 +/- 0.32) . Relationships of net N mineralization, flush of N following fumigation-in cubation, flush of CO2-C during the first day following rewetting of dried soil, particulate organic C and N, mean weight diameter of water-stable agg regation and total porosity with chloroform fumigation-incubation were also better without subtraction of a control than with subtraction of a control . In analyses of data taken from published reports, chloroform fumigation-i ncubation without subtraction of a control was better related with active s oil C pools than with subtraction of a control. Chloroform fumigation-incub ation without subtraction of a control, unlike that with subtraction of a c ontrol, should be considered a more robust method to determine microbial bi omass under a wide range of environmental conditions. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.