Soil constituents

Clays have layers of linked (Al, Si)04 tet-rahedra combined with layers of Mg(OH)2 or AI(0H)3- Clays are very important soil constituents and are used in pottery, ceramics, as rubber, paint, plastic and paper fillers, as adsorbents and in drilling muds. 

Of the various inorganic soil constituents, smectites (montmorillonite clays) have the greatest potential for sorption of pesticides on account of their large surface area and abundance in soils. Weak base pesticides, both protonated and neutral species, have been shown to be sorbed as interlayer complexes. Sorption of atrazine on smectites ranges from 0 to 100% of added atrazine, depending on the surface charge density of the smectite (36). 

Foreword in The Chemistry of Soil Constituents, Ed. D. J. Greenland and M. H. B. Hayes, John Wiley and Sons, (1978). 

Fig. 8-3 Diagram illustrating the development of positively and negatively charged sites on surfaces of soil constituents, at low and high pH. (Reproduced with permission from R. L. Parfitt (1980). Chemical properties of variable charge soils. In "Soils with Variable Charge" (B. K. G. Theng, ed.), p. 168. New Zealand Society of Soil Science Offset Publications.)...

Although iron (Fe) is one of the major soil constituents (0.5-5%), where it is usually present in the oxidized state (Felll), plant availability is severely limited by the low solubility of Fe-(hydr)oxides at pH levels favorable for plant growth. Therefore, plants need special mechanisms foraquiring Fe from sparingly soluble Fe forms to fit the requirements for growth, especially in neutral and alkaline soils, where the availability of Fe is particularly low (151). Mechanisms involved in iron acquisition by plants are also discussed in Chap. 8. 

D. B. Knaebel, T. W. Federle, D. C. McAvoy, and J. R. Vestal, Effect of mineral and organic soil constituents on microbial mineralisation of organic compttunds in a natural soil. Applied and Environmental Microbiology 60 4500 (1994). 

Aliphatic compounds Several water-soluble simple organic acids and alcohols are cannon plant and soil constituents. They include methanol, ethanol, n-propanol and butanol (40), and crotonic, oxalic, formic, butyric, lactic, acetic and succinic acids (41, 42), all of which inhibit seed germination or plant growth. Under aerobic conditions, however, aliphalic acids are metabolized in the soil and therefore, should not be considered a major source of allelopathic activity (40). 

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. 

Wettability measurements show that most soil constituents are water wettable or hydrophilic,28 although calcium carbonates [calcite, CaC03, and dolomite, CaMg(C03)2] are slightly hydrophobic for example, the contact angle of water and heptane is 100 to 105°. Therefore, carbonaceous reservoirs are usually oil-wet. 

Soil is the central organizer of the terrestrial ecosystem. Soil constituents, be they minerals, organic matter, or microorganisms, are of prime importance in governing interactive physical, chemical, and biological processes in soil environments. 

Kishi, H., Kogure, N., Hashimoto, Y. (1990) Contribution of soil constituents in adsorption coefficient of aromatic compounds, halogenated alicyclic and aromatic compounds to soil. Chemosphere 21, 867-876. 

Molybdate Reacts with various soil constituents Some mobility... 

Boron and arsenic are natural components of soil and are both present as oxyanions. Boron is present as boric acid or borate polymers, and arsenic is present as arsenate. While boron is weakly held by soil, arsenic is similar to phosphate in its interactions with soil constituents. Boron is an essential nutrient for plants however, it is also toxic to plants at relatively low levels. Arsenic is toxic. The laboratory chemistry of both of these elements is well understood, but their environmental chemistry, speciation and movement, is less well understood [23-27],... 

Soil pH is perhaps the most critical and common soil measurement where a definite amount of water is added before a measurement is made. Soil pH is a particularly complicated measurement because the proton can and does exist as a hydronium ion in the soil solution, as an exchangeable ion on the cation exchange sites, and bonded to various soil constituents. Because of these complexities, a soil sample is usually brought to a standard moisture content before a pH measurement is made. By bringing different soils to a common moisture content, they can be compared and analytical results from different laboratories will be comparable. Although there is a number of ways to measure soil pH, typically it is carried out using a pH meter and a pH electrode. 

The standard potentials of practically all oxidation and reduction reactions, especially those common in the environment and soil, are known or can easily be determined. Because of the specificity and relative ease of conducting voltammetric measurements, they might seem well suited to soil analysis. There is only one major flaw in the determination of soil constituents by voltammetric analysis and that is that in any soil or soil extract, there is a vast array of different oxidation-reduction reactions possible, and separating them is difficult. Also, it is not possible to start an investigation with the assumption or knowledge that all of the species of interest will be either oxidized or reduced. 

Because of the complex nature of soil and soil solutions, it is rarely possible to directly determine specific soil constituents by titrating soil or soil solutions using a pH meter, ion-specific electrode, or a platinum electrode (with appropriate reference electrode) [3],... 

The titrimetric determination of soil constituents is most commonly applied to a limited number of soil analyses, namely, organic carbon, nitrogen compounds, carbonates, and chlorides. Determination of acid content by titration is generally not done because the titration curves are not amenable to typical titration analysis. Because of the color of soil and the fact that it is a suspension when stirred, it is often necessary to remove the constituent of interest before titration. In other cases, it is possible to do a direct titration using an appropriate indicator. However, even in these cases, detection of the end point is difficult. 

XRF characteristics that can limit its usefulness are the surface area observed and surface contamination. In XRF, the surface area measured is small, meaning that a large number of determinations must be made in order to obtain a representative sample of the elements present. In addition, transport and storage of uncovered soil samples can lead to surface contamination that will subsequently appear as part of the soil constituents. 

The effect of mineral and organic soil constituents on the mineralisation of LAS, AE, stearyl trimethylammonium chloride (STAC) and sodium stearate (main soap component) in soils was studied by Knaebel and co-workers [38]. The four 14C-labelled compounds were aseptically adsorbed to montmorillonite, kaolinite, illite, sand and humic acids and subsequently mixed with soil yielding surfactant concentrations of about 50 jig kg-1. The CO2 formation in the serum bottle respirometers was monitored over a period of 2 months indicating that the mineralisation extent was highest for LAS (49-75%). Somewhat lower amounts of produced CO2 were reported for AE and the stearate ranging from 34-58% and 29-47%, respectively. The mineralisation extent of the cationic surfactant did not exceed 21% (kaolinite) and achieved only 7% in the montmorillonite-modified soil. Associating the mineral type with the mineralisation kinetics showed that sand... 

Since hot add hydrolysis was required to release practically all of the amino adds and amino sugars from the soils, it is likely that the amino adds occur in soils in the form of peptides, polypeptides, and proteins dosely assodated with and protected by SOM and inorganic soil constituents such as clay minerals and hydrous oxides of iron and aluminum. Similarly, amino sugars do not appear to exist in soils as free compounds. 

Hayes MHB, Swift RS (1978) In Greenland DJ, Hayes MHB (eds) Chemistry of soil constituents. Wiley, p 179... 

The principal fate of bromomethane in soil is volatilization, but some may react with organic soil constituents to yield nonvolatile end products, including bromide ion (Brown and Rolston 1980 Goring et al. 1975 Shiroishi et al. 1964). There is little evidence that bromomethane in soil is degraded by microorganisms (ERA 1986b). 

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