Elemental composition of soils

TABLE 1. Average Values for Elemental Composition of Soil Humic Substances... 

All comparisons of the elemental composition of soil humates with aquatic humates must be viewed with caution. In recent years, the extraction methodology has changed rapidly. A soil sample extracted with base in the classical manner may have up to 20% carbohydrate and up to 10% ash, while a sample extracted with XAD resins may have less than 2% carbohydrate and 2% ash. To compare two samples extracted by two different methods would be akin to comparing apples and oranges. Fortunately, a body of literature is accumulating which reports the properties of humates extracted by a single, well-defined method. 

From all these methods have come dark-brown materials, many of which fit the general range of elemental composition of soil humates. Table 3 lists some selected data. 

Depending on the controlling factors for mobility, the elemental composition of soils may or may not reflect the composition of the soil s parent material. However, it is generally observed that, all other factors being equal ... 

Walker et al. (2007) developed 6 QSARs to predict the toxicity of 17 cations to sunflower seeds (F.l. Helianthus annuus Sunspot) from the metal s physical properties and natural occurrence levels (Table 5.4). The QSARs predicted EC50 values based on the cation concentration producing a 50% inhibition of radicle growth one day after emergence. The QSAR developed with density of the elements (p), enthalpy of formation of metal sulfides (AHJ, and the stability constants of metal ions with sulfate (log Ki [sulphate]) produced the highest adjusted (Table 5.20). For natural occurrence levels, the QSAR developed with metal concentrations in soil (log Msoi,), the median elemental composition of soils (mg X/kg soil), and the calculated mean of the elemental content in land plants (Land Plants) produced the highest adjusted... 

Six non-physico-chanical properties have been used to predict cation toxicity (Table 5.21). These include serum concentrations, calmodulin activity, freshwater concentrations, abundance in the earth s crust, soil concentrations, and elemental composition of soils and plants. 

Observed stability constants of metal ion-acetato complexes Calculated constant of metal ion complexes with NH3 Enthalpy of formation of sulfides Stability constant of metal ion complexes with sulfate Average molar metal concentration in soil at 10% moisture Medians of elemental composition of soils Calculated mean of the elemental content in land plants Intrinsic (van der Waals) molecular volume... 

FACTORS AFFECTING THE TRACE-ELEMENT COMPOSITION OF SOILS 2.1 Introduction... 

Trace element composition of soils under permanent grass in rural and urban areas... 

Novel geochemical methods that can indicate the presence and composition of deep seated mineralization are therefore essential. In this study, the multi-element geochemistry of soils and their clay-sized fractions are compared for the deeply buried Talbot VMS Cu-Zn prospect, northern Manitoba, Canada. 

Both direct and indirect methods were tested in the Lisbon area. Direct methods include the assessment of hydrocarbon compositional signatures in surface soils, outcrop fracture-fill soils and mosses, and 6-ft (2 m) deep free-gas samples. Indirect methods pertain to the major and trace element chemistry of soils to look for alteration effects resulting from hydrocarbon microseepage. 

Raven KP, Loeppert RH. Trace element composition of fertilizers and soil amendments. J. Environ. Qual. 1997 26 551-557. 

Some of the above-mentioned limitations, but not all, can be overcome by making an extract of the soil and determining the elemental composition of the extract. This approach can eliminate or minimize problems associated with XRF analysis being limited to particle surface [34,35]. 

It should be emphasized that the deviations from the logarithmic correlation obey the normal distribution statistics, allowing one to apply convenient statistical procedures to analytical measurement results. As will be shown below, the logarithmic linear correlation rule was observed for all types of geo-chemical samples, i. e., snow, air, water, and soil. The correlation analysis of the elemental composition of melted-snow fractions showed with confidence level 95% that no significant discrepancy exists between the element composition within the correlation curves (see Table 1) and the corresponding variances are thus homogeneous for any two randomly chosen samples (i. e., points of the territory). 

One particular type of source that should be studied carefully Is entrained soil. As shown above, this Is often the greatest contributor of TSP In urban areas. As there Is so much of It present, we need to know concentrations of all measured elements quite well to make an accurate determination of the residual amounts left to be accounted for by other sources. The composition of selved soil Is often used for the soil component, but there may be considerable fractionation Imposed by entrainment, e.g., preferential selection of very fine clay mineral particles. Such fractionation has been demonstrated In the very limited studies of entrainment of particles from soil of known composition (e.g.. Refs. 21, 49). These studies can probably best be done In controlled environments such as wind tunnels. One cannot simply collect ambient particles In the countryside and consider it to be soil, as there are anthropogenic contributions even at great distances from cities ( ). There Is further confusion betwen clean, "continental" dust and "urban" dust. The latter, which Is usually collected near city streets (21, 50), typically has a composition of soil contaminated by anthropogenic emissions, especially from motor vehicles. 

The composition of soil aerosol, as indicated by elemental ratios, varies spatially. Calcium exhibits the greatest spatial variation relative to other soil elements. At most sites, little temporal variation exists. 

Another important application of this technique has been to determine the elemental composition of the lunar and Martian surfaces. Turkevich et al. (1969) constructed a rugged device to measure the backscattering of a particles from the lunar surface, which flew on three Surveyor missions in 1967-68 and yielded the first complete and accurate analysis of the lunar surface. The a particles came from a radioactive source (242Cm) that was part of the instrument package. The results of these experiments, which showed an unexpected and comparatively high abundance of Ti, were confirmed by laboratory analysis of lunar samples gathered in the Apollo missions. Since then, this technique has been used to study Martian rocks and soil. 

The elemental composition and related atomic ratios of HAs and FAs isolated from some representative organic amendments of various nature and source, and unamended and amended soils are shown in Table 4.2. Although the elemental composition of HAs and FAs show significant variability on dependence on the nature, origin, and treatment of the amendment, they generally feature larger H, N,... 

Ahmad, R., RN. Nelson, R.S. Kookana (2006). The molecular composition of soil organic matter as determined by 13C NMR and elemental analyses and correlation with pesticide sorption. Eur. J. Soil Sci., 57 883-893. 

Such methods are used in more fundamental studies to elucidate the soil chemistry, to determine the structure and composition of soil components and to improve understanding of the processes in the soil that control the mobilisation and retention of nutrient and toxicant elements in soil as well as to illuminate their transport mechanisms. They are, therefore, more important for the soil physical chemist than the functionally defined procedures that are the main concern of the agronomist. Both methods are of major interest to the environmental scientist particularly in the study of the fate of environmental pollutants. Many of the extractants intended to target particular species are also used in a functional speciation role. 

Table 12.4 Average of selected trace element compositions of the soil horizons (leach fractions), and the Penobscot Formation (whole rocks), Northport area... 

The approximate elemental composition of the earth s inorganic mineral surface is reported in Table 3,2. Elemental composition alone, however, cannot justify the unique properties of soil and how such properties influence the soil and water environment. The component that explains many of the physical and chemical properties of soil is the molecular arrangement of elements, forming structures with unique physicochemical properties. Soil mineral structures are briefly discussed below. 

Wallander, H., Johansson, L. Pallon, J. (2002). PIXE analysis to estimate the elemental composition of ectomycorrhizal rhizomorphs grown in contact with different minerals in forest soil. FEMS Microbiology Ecology, 39, 147-56. 

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