Humus, acid

Nonhumic substances Compounds belonging to known classes of biochemistry, such as amino acids, carbohydrates, fats, waxes, resins, and organic acids. Humus probably contains most, if not all, of the biochemical compounds synthesized by living organisms... 

One of the first comprehensive studies of the chemical nature of humic substances was carried out by Sprengel (1826, 1837). The procedures he developed for the preparation of humic acids became generally adopted, such as pretreatment of the soil with dilute mineral acids to enhance extraction with alkali. Sprengel concluded that, for soils rich in bases, humic acid was in a bound form consequently, the soil had a neutral reaction (contained mild humus ). This soil was regarded as highly fertile. On the other hand, for soils poor in bases, the humic acid was believed to be in the free form, with the result that the soil was acid and unproductive (contained acid humus ). A major contribution of Sprengel to humus chemistry was his extensive studies on the acidic nature of humic acids. 

Humic acid Soluble in alkali, precipitated by acid Humus acid Humic acid Humic acid Humic acid Humus acid Humic acid... 

The following day the acid liquid is filtered with suction through a large Buchner funnel, to remove large quantities of humus which are produced. The humus on the filter is washed with two 350-cc. portions of water and finally with two 300-cc. portions of benzene. The filtered liquid and aqueous washings have a volume of approximately 10 1. The s-methylfurfural is... 

Humus The dark organic material in soils, produced by the decomposition of soils. The matter that remains after the bulk of detritus has beenconsumed (leaves, roots). Humus mixes with top layers of soil (rock particles), supplies some of the nutrients needed by plants -increases acidity of soil inorganic nutrients more soluble under acidic conditions, become more available, EX. wheat grows best at pH 5.5-7.0. Humus modifies soil texture, creates loose, crumbly texture, that allows water to soak in and nutrients retained permits air to be incorporated into soil. 

Humus-saure, /. humic acid, -schicht, /. layer of humus, -stoff, m. humus substance. Hund. m. dog hoimd (Mach.) rammer, monkey (Mining) car. 

To protect buried metals from premature breakdown it must suffice to say that protective coatings and other methods must be applied against factors such as the effects of galvanic currents, composition of the moisture in the ground, humus acids, bacteria, etc. (See Section 14.8.)... 

A preliminary test for the biodegradability of the 3-phenyl- and 3-carbamoyl-2(lH)pyridones was conducted in a barnyard humus suspension. The analysis by HPLC showed some loss, and the fluorescent compounds seemed to be adsorbed onto the solid. The 3-carbamoyl-2(lH)pyridone (II) also hydrolyzed to 3-carboxylic acid-2(lH)pyridone both in the slurry test and in water solutions that had been left standing 1-2 weeks. In preliminary tests both the 3-phenyl- and the 3-carbamoyl-2(lH)pyridones apparently adsorbed to some extent on silica sand columns. In addition, the solubility of both 1-H compounds was somewhat low, 1.3 x 10 M for II, and 1.0 x 10 M for IV. 

Long-term grasslands provide plenty of organic matter for humus formation. If the soil is not acidic or waterlogged, the soil fauna and flora create humus and the subsequent useful development of a porous crumb and granular structure. Porosity encourages root growth and the uptake of soil nutrients. 

Some compounds, i.e. benzoic and cinnamic acids are not protected against biodegradation to a high degree by linkage and/or absorption on soil constituents such as clay or humus (184), hence they may have a rapid turnover rate in soils. 

Incorporation of some xenobiotics (herbicides) into soil humus-complexes occurs via pathways analogous to those for incorporation of naturally occurring phenolic and benzoic acids and do indeed involve phenolic and humus-like constituents... 

Pennanen T (2001) Microbial communities in boreal coniferous forest humus exposed to heavy metals and changes in soil pH a summary of the use of phospholipids fatty acids, Biolog and H-thymidine incorporation methods in field studies. Geoderma 100 91-126... 

Transformation of the initially deposited remains of living organisms started in the water columns and in the upper layers of bottom sediments of ancient seas. Random polymerization and condensation reactions of degraded biopolymers are believed to have formed the initial geopolymers, which contain humin, fulvic and humic acids. Until now these compounds (very typical for soil humus as well) are... 

Many researchers have attempted to unravel the mystery of the structure of humus. One approach has been to isolate fractions by extracting humus using various extraction procedures. These procedures result in the isolation of three or more fractions humic acid, fulvic acid, and humin. Humic material is isolated from soil by treating it with alkali. The insoluble material remaining after this treatment is called humin. The alkali solution is acidified to a pH of 1.0 and the precipitate is called humic acid, while the soluble... 

Figure 4.10. Humus with cation exchange sites created by the ionization of phenolic and acidic functional groups. The M+ represent exchangeable cations.

Figure 4.11. The carboxylate anion (an ionized acid) and a phenoxy (the anion of phenol) groups. The R stands for the rest of the humus molecule to which these groups are attached.

Once ionized, the acidic and phenolic molecules carry a negative charge and can thus attract cations and participate in the CEC of soil that are part of humus. The contribution of this source of negative charge will depend on the pH of the soil solution and will change as the pH changes. Thus, the CEC is pH dependent. For this reason, it is essential that the CEC values are measured at the same pH when comparing different soil samples. 

Soil aluminosilicates + other minerals + humus + organic matter + strong mineral acids (HC1, HN03> H2S04, H3PO4)... 

Newer and more complex humus extractions have been developed. These typically involve more steps such as both physical separation on the basis of density and particle size (related to the size of soil inorganic components), and chemical separation based on extractions and washings with hydrofluoric acid (HF), hydrochloric acid (HC1), and sodium hydroxide (NaOH). The products of such separations are then subjected to spectroscopic analysis and interpretation [22,23],... 

Humic and fulvic acids contain various types of phenolic and carboxylic functional (hydrophilic) groups as well as aromatic and aliphatic moieties which import hydro-phobic properties to these substances. Fig. 4.12 gives a schematic idea on the composition of these substances. We refer to the book of Thurman (1985) and Aiken et al. (1985) for a description of the various properties of humic and fulvic acids in soils and waters and the book by Buffle (1988) for the coordinating properties of humus and humic acids. 

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