ARS | Publication request: RELATIONSHIPS OF CHLOROFORM FUMIGATION-INCUBATION TO SOIL ORGANIC MATTER POOLS

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 1998
Publication Date: N/A

Interpretive Summary: Microbial biomass is part of the active pool of soil organic matter that plays focal roles in decomposition of organic materials, nutrient cycling, and biophysical manipulation of soil structure. Determination of microbial biomass can be made using several biochemical analyses developed within the past two decades. The method by which all other methods are compared is the chloroform fumigation-incubation method with subtraction of a control. However, considerable debate has been engaged by soil ecologists since the method's inception as to the nature and validity of the control. We compared two commonly used variants of the chloroform fumigation-incubation method to their relationships with other active, passive, and total soil C and N pools in soils from Texas, Georgia, Alberta, and British Columbia. Several active, passive, and total soil organic matter pools were much more closely related with chloroform fumigation-incubation without subtraction of a control than with subtraction of a control. Our data from several soils under different management scenarios is overwhelmingly in support of not subtracting a control to estimate microbial biomass.

Technical Abstract: We compared two commonly used variants of the chloroform fumigation-incubation method to their relationships with other active, passive, and total soil C and N pools in soils from Texas, Georgia, Alberta, and British Columbia. The relationship of potential C mineralization with chloroform fumigation-incubation without subtraction of a control was much stronger (R-square = 0.81 among five data sets with a total of 844 observations) than with subtraction of a control (R-square = 0.30). Similarly, the relationship of soil organic C with chloroform fumigation-incubation without subtraction of a control was better (R-square = 0.80) than with subtraction of a control (R-square = 0.38). Relationships of net N mineralization, particulate organic C and N, mean weight diameter of water-stable aggregation, and total porosity with chloroform fumigation-incubation were also better without subtraction of a control than with subtraction of a control. Chloroform fumigation-incubation without subtraction of a control, unlike that with subtraction of a control, should be considered a more robust method to determine microbial biomass under a wide range of environmental conditions.