Chloroform fumigation technique as a means of determining the size of specialized soil microbial populations: Application to pesticide-degrading microorganisms

A method is proposed for studying the dynamic behaviour of the soil microbial population involved in the degradation of 2,4-D. The method is based on in situ specific-labelling of that population following treatment of the soil with ¹⁴C-labelled herbicide and investigating the kinetics of the incorporation of radioactivity by the soil microflora in treated soil samples subjected to the chloroform-fumigation technique after varying periods of exposure. Non-degraded herbicide still present in the soil after fumigation did not affect the overall flush of CO₂ and was not further broken down at a sufficient rate to appreciably contribute to ¹⁴CO₂ evolution. The validity of the method to assess the soil biomass of the 2,4-D degrading population together with its time variations is discussed in relation to the position of the ¹⁴C on the pesticide molecule.