Humification extent

In the case of humification, nitrogen compounds react to a different extent in these stages of the reactions when aromatic components are involved. The extent of nitrogen fixation depends on die available o-amino nitrogen compounds and the environmental conditions (9). In the case of natural humification, the biological processes can be considered more or less finished at this stage. 

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. 

It is desirable to have at least a semiquantitative estimate of the extent of humification, or degree of decomposition of a peat material, since this is a prominent feature of all aspects of natural and economic roles of peatlands. Many avenues are available for achieving this objective because humification involves numerous reactions and results in various products and effects as discussed by Stevenson in Chapter 2. 

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. 

By using methods analogous to those in the above studies Zelazny and Carlisle (1974) found that oxygen-containing functional group levels in humin and humic and fulvic acids from all series and layers of the Florida mucks were similar (Table 13), irrespective of their extents of humification or rates of subsidence. 

Attempts at characterizing peat humus through spectroscopy and chemical degradation procedures (Walmsley, 1973 Stevenson, 1974 Fuchsman, 1980) also have shown that peat humic substances are similar to those from mineral soils. For example Levesque et al. (1980b) found that humic substances extracted by sodium pyrophosphate from 10 different peat materials that varied in botanical origin and extent of humification yielded aliphatic and phenolic compounds and benzenecarboxylic acids (Table 14) in amounts... 

TABLE 11. Major Functional Groups (meq/g) in Organic Soils Varying in Their Extent of Humification"... 

Humic substances are typical products of the humification process. They are the basic component of the humus, occurring in the humus material to the extent of 80 to 90%. They consist of a group of acid, yellow to dark brown polymeric substances of a heterogeneous aromatic and polydisperse character. Their acid nature allows them to react with mineral substances to form stable organomineral complexes sometimes referred to as humines. They differ from the remaining organic material in the soil by various typical features as follows ... 

The microorganisms surrounding the roots are active in the breakdown of any crop residues or other energy sources, and in the overall humification process. Since the rhizosphere organisms are known to be more active than are those located elsewhere in the soil mass (Katznelson, 1960), it follows that this humification process in the rhizosphere is accelerated at least to the extent that the numbers are increased. Starkey (1931a) observed such a correlation. 

The process of direct anaerobic-aerobic treatment resulting in humification of TNT and its congeners offers a convincing and simple concept (Fig. 18 process II) for the remediation of soil contaminated with TNT and congeneric compounds. This is evident by comparison with the alternative process I (Fig. 18), which requires the desorption of the contaminants by innocuous solvents such as methanol or ethanol. Desorption plus the separation of particles must precede the actual anaerobic process of polynitrotoluene reduction. Furthermore, the anaerobic stage requires a microbial system which degrades TAT and diaminotoluenes productively or at least to such an extent that subsequent aerobic treatment results in complete mineralization. 

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