Humification measurement

A spectroscopically demonstrated molecular property of SOM relating to the degree of humification is the SFR concentration, as measured by EPR (Riffaldi and Schnitzer, 1972 Schnitzer and Levesque, 1979 Martin-Neto et al., 1991 Senesi et al., 1996 Jerzykiewicz et al., 1999 Watanabe et al., 2005). The content of paramagnetic species is proportional to the EPR spectrum area that can be obtained by double integration of the first derivative EPR spectrum, which is normally detected. An approximation commonly used to obtain the relative area of free radicals is the... 

A number of UV-vis absorption ratios have been measured to provide information about the state of humification and content of humic material in the dissolved organic carbon (DOC). For example, the ratio of the ultraviolet absorbance at 254 nm (UV254) with the DOC content provides an estimate of the abundance of ultraviolet absorbing species and may also be used for comparison of the aromaticity of various humic materials (McDonald et al., 2004). 

Figure 16.39. Data showing correlation among fluorescence methods to determine humification degree of HA. A4AX is the humification index proposed by Zsolnay et al. (1999) it is calculated through the ratio between areas of the upper quarter of emission spectra (435-480nm) and the lower quarter (30( M45 nm) when excitation is made at 240nm. Iv is the humification index proposed by Kalbitz et al. (1999) it is calculated through the ratio of peak intensities in 465 and 399 nm measured in fluorescence synchronous-scan excitation spectra. A46S is the humification index proposed by Milori et al. (2002) it is calculated by fluorescence area of emission spectra when the excitation is made at 465 nm.

Peatlands, or organic soils, are water-logged deposits of partly decomposed plant debris. Ecological variation and diversity in extent of domination by water influence the degree of humification in peatlands. Humification in peatlands does not coincide with decomposition as well as in mineral soils. Measurement and extraction of peatland humus are hampered by the presence of large proportions of unhumified material. Therefore, most studies on the characterization of peatland humus have focused on humic acids, or on pyrophosphate extracts of the organic soils. Pyrophosphate extracts contain less unhumified materials than alkali extracts but are far less effective in extracting the peat humic substances. 

Visual and microscopic examination of peats are helpful only to a limited extent for determining botanical origin, because the characteristic anatomical features become indiscemable as the material becomes amorphous due to decomposition. Estimation of the percent of amorphous materitd (degree of decomposition or the von Post scale) (Post and Granlund, 1926) by microscopic examination, as a measure of the extent of humification, is handicapped by the fact that all amorphous material is not humus. 

Pyrophosphate Index. An index of the degree of humification of organic matter as measured by the determination of the absorbance of the pyrophosphate extract using a colorimeter. 

The differences between samples of annexes (1, 2 and 3) and samples of the pond (4, 5) are the crests of the peaks. An evolution or humification index could be the ratio of the absorbance measured at these two wavelengths. The study of the C/N ratio evolution shows a gradient of mineralisation from the annexes to the Grand Mare. 

The Development of a Fluorescence Index to Measure Organic Matter Humification Preserved in Cave Stalagmites and Create Long-Term Records... 

Figure 9.11. A 1000-year record of organic matter humification preserved in a cave stalagmite, (a) The annual hand width (annual accumulation rate) of the stalagmite as determined hy counting annual hands formed from fluorescent organic matter, (b) The fluorescence ratio as determined by measuring the intensity of emitted fluorescence at 420 and 470 nm. Low ratios (note the inverse scale) correlate with periods of faster stalagmite growth due to a decrease in water table in the overlying peat and increased COj production and limestone dissolution. Low ratios therefore correspond to periods of high humification. (Adapted from Proctor et al., 2000.)...

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