An Alternative Method for Quantifying Soil Microbial Activity.

Microbial respiration is regarded as an important indicator of overall soil health, however it can be somewhat difficult to accurately measure because of the heavy variability that inevitably comes with biologically mediated phenomenon. The Solvita Soil Respiration test, which quantifies soil microbial activity as a function of CO₂ evolution from soil samples, has become widely accepted by many soil testing labs as an easy to use and easily replicable method of soil analysis. The objective of this study was to examine CO₂ evolution from soil samples using the Solvita testing method and to establish an alternative soil microbial testing method that would provide results similar to the Solvita test.  A series of 18 soil samples were collected from around the state of Oklahoma, and analyzed using both the Solvita CO₂ Burst method and a direct measurement of CO₂ evolution using a Varian 450 Gas Chromatograph at 4 drying temperatures. Comparing the test results revealed a close correlation among the procedures when Solvita CO₂ values where less than 180 mg kg-1 which is the detection limit for the method.  This detection limited was observed for 5 of the 18 samples analyzed at drying temperatures of 45 and 65 degrees C.  In contrast, the gas chromatograph method allow detection of differences in CO₂ emitted from these samples at all temperatures except for 105 degrees C, at which microbial activity was negatively impacted by temperature.