Submitted to: Canadian Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/1999
Publication Date: N/A
Interpretive Summary: Soil microbial biomass is composed of fungi, bacteria, actinomycetes, and protozoa. These microscopic organisms are important agents for the decomposition of organic amendments, cycling of nutrients, and formation of soil structure. A wide variety of methods is currently available for holistically determining the entire population of microorganisms in soil, although agreement among methods is not adequate. We compared one of the oldest methods (chloroform fumigation-incubation with subtracting a control) to other methods for assessing biological soil quality. Chloroform fumigation-incubation without subtraction of a control was the best related to other factors that should control the size of the microbial population, such as total organic carbon and potentially mineralizable carbon. Effects of land management systems that altered the quantity and quality of organic carbon inputs were highly sensitive with chloroform fumigation-incubation without subtracting a control, but less so with subtraction of a control. Chloroform fumigation-incubation without subtracting a control is a robust and reliable method to assess biological soil quality under a wide range of soil conditions.
Technical Abstract: Microbial biomass, as part of the active pool of soil organic matter, is critical in decomposition of organic materials, nutrient cycling, and formation of soil structure. We evaluated chloroform fumigation-incubation with (CFI/F-C) and without subtraction of a control (CFI/F) as methods to assess biological soil quality. Relationships between CFI/F and potential C mineralization, particulate organic C, and soil organic C were stronger (r-square = 0.86, n=232) than those between CFI/F-C and the same soil C pools (r-square = 0.25) in soils from Georgia. From published data, relationships of CFI/F with potential C mineralization and soil organic C were stronger than those of chloroform fumigation-extraction and substrate-induced respiration with these soil C pools. Effects of land management on biological soil quality using CFI/F were consistent with those determined using other soil C pools as response variables. However, land management effects on biological soil quality using CFI/F-C were either contrary to those using other soil C pools or not detectable because of greater inherent variability in CFI/F-C. Chloroform fumigation-incubation without subtraction of a control is a robust and reliable method to assess biological soil quality under a wide range of soil conditions.