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Soil humic components isolation

The Emergence of Procedures for the Isolation of Soil Humic Components 4... [Pg.1]

Vauquelin (14), A. Klaproth (6), and R. Jameson (5), alkali soluble organic constituents of soil and coal are designated as humic acids/ Collectively, these substances make up an ill-defined series of dark colored, weakly acidic solids which form whenever plant components (such as lignin) are exposed to fungal oxidases, or when coal is allowed to weather or otherwise oxidize. Some evidence now exists that humic acids isolated from these varied sources do indeed contain several common peripheral structures (2, II, 16), but by any more discriminating test, the term possesses little chemical significance or fixed meaning. [Pg.614]

Soil polysaccharides can amount to as much as 20% of the humic fractions isolated in aqueous media, and identification of the classes of components in humin materials in associations with the soil clays indicates that carbohydrates contribute significantly to those isolated in the DMS0/H2S04 medium (see Sections 1.4.7 and... [Pg.25]

Though plants are the predominant source of most of this material, microbial inputs are important as well (Cheshire, 1977). Carbohydrate extracts from soils and sediments probably contain only a small fraction of the total carbohydrate concentration since much of the carbohydrate content appears to be polysaccharides bound to the humic components (Lowe, 1978), and probably to clay minerals as well. Its presence is recognized by the release of simpler sugars upon hydrolysis of the sample (Greenland and Oades, 1975 Lowe, 1978). Isolated polysaccharide fractions are generally polydisperse mixtures. [Pg.115]

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). [Pg.488]

Structural Studies of Humic Substances. Solid-state C NMR has played a major role in past studies of the chemical structure of humic substances isolated from soil as mentioned above. Recent studies have focused on the examination of humic substances from various environments to establish variabihties which might be indicative of structure and structural evolution.(29-34) Also, combined use of NMR with other analytical methods such as analytical pyrolysis, chemical degradative methods, and solution NMR studies has proved vduable in elucidating structural components. However, the complexity of humic substances has precluded all but inferred structures based on these combined studies. [Pg.64]

SCHNITZER M., MARSHALL P.R. and HINDLE D.A. 1983. The isolation of soil humic acid fulvic acid components rich in "unknown nitrogen", Canadian Journal of Soil Science, 63, 425-433,... [Pg.325]

Humic acid is composed of aromatic, aliphatic and carbohydrate carbon compounds. An average humic acid s elemental composition is 55.1% C, 5.0% H, 3.5% N, 35.6% O, and 1.8% S (Rice and MacCarthy, 1991). Its molecular weight distribution is typically broad, and it is a relatively high-molecular-weight material relative to the fulvic acid isolated from the same soil or sediment. It s predominantly functionalized by carboxylic acid and phenolic groups. At least some components of humic acid are surface-active, and these components have been shown to form micelles in concentrated, alkaline aqueous solutions (Piret et al., 1960 Visser, 1964 Wershaw et al., 1969 Tschapek and Wasowski, 1976 Chen et al., 1978 Rochus and Sipos, 1978 Hayano et al., 1982 Hayase and Tsubota, 1984 Guetzloff and Rice, 1994). [Pg.115]

The cloning of functional genes from natural microbial consortia is dependent on the high quality of the extracted and purified environmental DNA since the enzymatic modifications required during the cloning steps are sensitive to contamination by various biotic and abiotic components that are present in environmental ecosystems. For example, extraction of DNA from soils always results in coextraction of humic substances, which interfere with restriction enzyme digestion and PCR amplification and reduce transformation efficiency and DNA hybridization specificity [19 -22], Therefore, extraction methods have been developed to remove or minimize contamination of the purified DNA by humic or other interfering substances. Several protocols for the isolation of bacterial community DNA from various environmental samples have been reported in recent years. These methods are based either on re-... [Pg.65]

Humin isolates from sediments of the Mew York Bight and Potomac River estuary have spectra that are notably different in that aromatic carbons are the dominant components. The spectra resemble that of humin isolated in the same manner from an aerobic soil from southern Georgia (Figure 5). However, unlike the humin from soil which shows a significant peak for carboxyl carbon (175 ppm), spectra of humin from the New York Bight and the Potomac River do not display a discreet peak at 175 ppm and appear to be depleted of carboxy 1/amide groups. Elemental data for these humins (19) are consistent with the NMR results. Atomic H/C ratios of less than 0.8 are not typical of humic material but more like those of highly aromatic coal or coal-like products. The NMR spectra also resemble... [Pg.150]

X-ray spectra of phosphorus in natural organic molecules. The P NEXAFS spectroscopic studies conducted on isolated humic substances and soil organic molecules indicate that the primary form of P is phosphate and phosphonate (Fig. 24 Myneni and Martinez 1999). When compared to humic substances from soil systems, the fluvial humic substances exhibit phosphonate as one of the important components. However, phosphonate constitutes only a minor fraction of total P in humic substances. Soil samples also exhibit features that correspond to polyphosphate. Another study conducted using NEXAFS spectroscopy at the P absorption edge suggested that marine sediments and humic materials do not exhibit phosphonate and the P NEXAFS spectra of these samples more closely resembled that of hydroxyapatite (Vairavamurthy 1999). [Pg.519]

Natural organic polyelectrolytes are some of the most active components of natural soil-water systems entering into physical and chemical reactions with practically all other components of the systems. Most pesticides are strongly sorbed by insoluble natural organic polyelectrolytes, such as humic acid. The soluble humic salts, however, may solubilize insoluble pesticides. Pesticides also enter into chemical reactions with natural organic poly electrolytes. The mechanisms of most of these interactions have not yet been elucidated. Elucidation will require isolation of well-defined, chemically and physically homogeneous natural polyelectrolyte fractions. [Pg.149]

The Humus Theory was popular because it combined, in an uncritical way, the views of chemists and biologists of the period. The chemists had isolated a group of humus components, the humic acids, which were soluble in alkalis but insoluble in water. It,therefore,seemed reasonable to suggest that alkalis and alkali earths present in the soil would dissolve the humus and make it available to plant roots. [Pg.40]


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See also in sourсe #XX -- [ Pg.4 , Pg.5 ]




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