Assessing biological soil quality with chloroform fumigation-incubation: Why subtract a control?

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 subtraction of a control (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 (r2 = 0.86 ± 0.07, n = 232) than those between CFI/F–C and the same soil C pools (r2 = 0.25 ± 0.09) 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. Key words: Active soil carbon, chloroform fumigation-extraction, microbial biomass, soil organic matter, soil quality, substrate-induced respiration