Fumigation-extraction method

Inubushi, K., Brookes, P. C and Jenkinson, D. S. (1991). Soil microbial biomass C, N and ninhydrin-N in aerobic and anaerobic soils measured by the fumigation-extraction method. Soil Biol. Biochem. 23,737-741. 

ISO 14240-2 1997 Soil quality - Determination of soil microbial biomass -Part 2 Fumigation-extraction method. 

Table 7.2. Overview of fumigation extraction methods for microbiai phosphorus determination. 

Reference and method number Fumigation Extraction method Sorption correction Phosphorus fraction Conversion factor K ... 

Microbial phosphorus is quantified after fumigation of soil with chloroform or hexa-nol to kill soil microorganisms (Brookes et al., 1982). The various modifications of the method, especially in terms of extractants and use of calibration factors, are described elsewhere in this volume (see Oberson and Joner, Chapter 7). For highly weathered tropical soils, the fumigation-extraction method with anion exchange resin membranes (Kouno et al., 1995) or Bray (NH F-HCl) extraction (Oberson et al., 1997) may be most suitable. 

P. C. Brookes, L. Landman, and D. S. Jenkin.son, Chloroform fumigation and the release of soil nitrogen a rapid extraction method to measure microbial biomass nitrogen in soil. Soil Biol. Biochem. 17331 (1985). 

Brookes, P. C., Landman, A., Pruden, G., and Jenkinson, D. S. (1985). Chloroform fumigation and the release of soil nitrogen A rapid direct extraction method to measure microbial biomass nitrogen in soil. Soil Biol. Biochem. 17, 837-842. Brookes, P. C., Powlson, D. S., and Jenkinson, D. S. (1982). Measurement of microbial biomass phosphorus in soil. Soil Biol. Biochem. 14, 319-321. 

Reference and method number Microorganisms added for determination Number of soils Fumigant Extractant Kp (for phosphate) Kp (for total phosphorus) ... 

Various other workers have reported on the determination of volatile organic compounds in soils [186,187] and landfill soils [188]. Soil fumigants such as methyl bromide have also been determined by this technique [189]. Trifluoroacetic acid is a breakdown product of hydrofluorocarbons and hydrochlorofluorocarbon refrigerant products in the atmosphere and, as such, due to the known toxicity of trifluoroacetic acid, it is important to be able to determine it in the atmosphere, water and in soil from an environmental point of view [190]. In this method the trifluoroacetic acid is extracted from the soil sample by sulfuric acid and methanol, which is then followed by the derivatisation of it to the methyl ester. The highly volatile methyl ester is then analysed with a recovery of 87% using headspace gas chromatography. Levels of trifluoroacetic acid in soil down to 0.2 ng/g can be determined by the procedure. 

Vance, Brookes, and Jenkinson (1987) first showed a close linear relationship between biomass C measured by the FI method and Ec, where Ec= [(organic C extracted by 0.5 molar (M) potassium sulfate (K2S04), soil fumigated for twenty-four hours) minus (organic C extracted from a similar, nonfumigated soil)]. They proposed that biomass C can be estimated from the relationship, Biomass C = 2.64 Ec. 

Methods used to quantify microbial phosphorus have so far been based on fumigation and extraction. The basic methods were published early in the 1980s (Brookes et al., 1982 Hedley and Stewart, 1982) and, of the methods presented in Table 7.2, that of Brookes et al. (1982) has been used the most frequently. Phosphorus released by fumigation is calculated as the difference between inorganic or total phosphorus extracted from fumigated and non-fumigated soil. Most phosphorus in microbial cells is... 

The original methods have been modified to increase the accuracy of microbial phosphorus estimates on specific soils, and different protocols now exist for each step of the method (Table 7.2). Chloroform is most commonly used as fumigant, either gaseous, liquid or both. The non-carcinogenic hexa-nol is also effective as a fumigation biocide (McLaughlin et al., 1986) and must replace chloroform when certain brands of resin strips are used for extraction, since these are damaged by chloroform (Biinemann et al.,... 

For fumigation and extraction the method with the corresponding number described in Table 7.2 was followed. 

There are many published TLC protocols that can be used to separate flavonoids that have been extracted from tissue samples and juice. Methods include the use of silica, reverse phase or polyamide plates in a wide variety of solvent systems. Many of these solvent systems are published in a chapter on flavonoids in Kirchner s book on TLC (1967). The flavonoid spots on the developed plates can be visualized in a variety of maners, the most common method being the direct visualization under UV light using plates that have an acid-stable fluorescent indicatior added for visualization at 254 nm. The visualized spots can then be scraped and quantified by UV absorption. Another standard visualization method utilizes a spray of 2% sodium borohydride freshly prepared in methanol followed by fumigation with hydrogen chloride gas (Horowitz 1957). 

Two new methods for measuring soil microbial P have been described, based on the widely used CHCI3- fumigation procedure for measuring the soil microbial biomass. In these methods, the P released from microbial cells following lysis with CHClg is extracted from the soil with NaHCO. Some of this P will be immediately fixed by soil colloids, and in one methoda spike of P is used to correct for this. The other method is calibrated for recovery of microbial P for each soil type. Non-microbial P was not affected to any extent by fumigation. 

The two methods, while similar in principle, differ in some respects. Microbial P is calculated from the difference in extractable P. or P between fumigated and unfumigated soil. 

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