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Arid Land Research and Management

Anna Beriozkin- Department of Soil Chemistry, Plant Nutrition and Microbiology Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization (ARO), Volcani Center, Rishon LeZion, Israel;

 

The potential overestimation of soil microbial biolmass C, using the fumigation-extraction method, arising from the contribution of residual (i.e., non-evacuated) chloroform (CHCl3) to the fumigation flush of C, was recently shown to be minor for agricultural topsoil samples. However, we hypothesized larger flush proportions of residual CHCl3–C, and hence greater biomass overestimations in low-biomass, subsoil samples due to the characteristically lower fumigation flushes of C in subsoils. The depth stratification (0–100 cm) of fumigation-extractable C and CHCl3–C was determined in six soil profiles (three loesses ranging from 6 to 20% clay and three vertisols ranging from 46 to 69% clay). Residual chloroform levels correlated positively with soil organic matter content but not with clay content and decreased down the profiles. Residual chloroform contributed ∼2.0% to biomass-C overestimation, independent of soil type or depth, thus refuting the study hypothesis and supporting the safe use of the fumigation-extraction method also with subsoil samples.

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The assessment of microbial biomass C in subsoil samples using fumigation-extraction is negligibly affected by residual chloroform

Anna Beriozkin- Department of Soil Chemistry, Plant Nutrition and Microbiology Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization (ARO), Volcani Center, Rishon LeZion, Israel;

 

The assessment of microbial biomass C in subsoil samples using fumigation-extraction is negligibly affected by residual chloroform

The potential overestimation of soil microbial biolmass C, using the fumigation-extraction method, arising from the contribution of residual (i.e., non-evacuated) chloroform (CHCl3) to the fumigation flush of C, was recently shown to be minor for agricultural topsoil samples. However, we hypothesized larger flush proportions of residual CHCl3–C, and hence greater biomass overestimations in low-biomass, subsoil samples due to the characteristically lower fumigation flushes of C in subsoils. The depth stratification (0–100 cm) of fumigation-extractable C and CHCl3–C was determined in six soil profiles (three loesses ranging from 6 to 20% clay and three vertisols ranging from 46 to 69% clay). Residual chloroform levels correlated positively with soil organic matter content but not with clay content and decreased down the profiles. Residual chloroform contributed ∼2.0% to biomass-C overestimation, independent of soil type or depth, thus refuting the study hypothesis and supporting the safe use of the fumigation-extraction method also with subsoil samples.

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