Molar concentration of K2SO4 and soil pH affect estimation of extractable C with chloroform fumigation-extraction

• Published in: Soil biology & biochemistry 2001-09, Vol.33 (11), p.1501-1507
• Main Authors: HANEY, R. L, FRANZLUEBBERS, A. J, HONS, F. M, HOSSNER, L. R, ZUBERER, D. A
• Format: Article
• Language: English
• Subjects: acid soils; Agronomy. Soil science and plant productions; alkaline soils; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; chloroform; clay; colloids; flocculation; fumigation; Fundamental and applied biological sciences. Psychology; microbial biomass; Microbiology; mineralization; Physics, chemistry, biochemistry and biology of agricultural and forest soils; potassium sulfate; soil microorganisms; soil organic carbon; soil pH; Soil science
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/S0038-0717(01)00065-7

Methods of determining soil microbial biomass need to be reliable and produce consistent results across soils with a wide range of properties. We investigated the effect of extractant molarity (distilled water and 0.001, 0.01, 0.1, and 0.5 M K2S04) on the flush of C (i.e. the difference between fumigated and unfumigated subsamples) with the chloroform fumigation-extraction method in soils of different pH. Extraction efficiency of 0.5 M K2S04 relative to water was dependent upon soil pH. The ratio of extractable C in water to that in 0.5 M K2S04 for five acidic soils was 1.5 ± 0.3 in unfumigated controls, 1.4 ± 0.2 in fumigated samples, and 1.8 ± 0.7 in fumigated minus control flushes, respectively. Ratios in six alkaline soils were 1.0 ± 0.2, 0.9 ± 0.2, and 0.8 ± 0.2, respectively. Flocculation/dispersion of organic colloids and changes in the diffuse double layer surrounding clay particles are possible reasons for differences in extractable C with changes in extractant molarity and soil pH. Chloroform fumigation-extraction with any of the extractants was less related to soil organic C and potential C and N mineralization during 50 days of incubation (r2 = 0.51 ± 0.11) than was chloroform fumigation-incubation without subtraction of a control (r2 = 0.74 ± 0.08). Changes in microbial biomass estimates with changes in extractant molarity and soil pH suggest that chloroform fumigation-extraction may not be reliable in a wide range of soils.