Soils parent material

Bioavailable trace elements in world arid and semi-arid soils vary widely, depending upon the nature of the parent materials, soil pH, CaC03 and clay content, and soil texture. The contents of bioavailable trace elements in arid and semi-arid soils of selected countries are presented in Table 7.6. The data are recalculated from Sillanpaa (1982) and cited from Liu (1996), Han and Banin (1997, 1999) and many others. 

C-horizon (parent material). Soil parent materials are those from which the soil was formed. 

Hanley, P.K. and Murphy, M.D. (1970) Phosphate forms in particle size separates of Irish soils in relation to drainage and parent materials. Soil Science Society of America Proceedings 34,... 

Figure 4. Occurrence and transformation of mica in the parent material—soil system.

There are areas (22) where selenium levels in the soil are very low these include regions of volcanic activity like that adjacent to the Cascade mountains in the Pacific Northwest states of the United States and the central north island of New Zealand. There, because the heat of emption volatilized the selenium, the residual soil parent material is virtually devoid of selenium. Other areas of low soil-selenium reflect leaching of selenium out of the top soil, as in the Canterbury plain on New Zealand s south island. Areas of selenium deficiency have negative implications for animal and human health. 

The condition of any soil represents a stage in the changing process of soil evolution. Soils develop, mature and change with the passage of time. Whereas the time required for a true soil to develop from the parent rock of the earth may be thousands of years, rapid changes can result in a few years when soils are cultivated, irrigated, or otherwise subjected to man s manipulation. The type of soil that develops from the parent material will depend upon the various physical, chemical and biological factors of the environment. 

The weathering process which eventually reduces the rock of the parent material to the inorganic constituents of soil comprises both physical and chemical changes. Size reduction from rocks to the colloidal state depends not only upon the mechanical action of natural forces but also on chemical solubilisation of certain minerals, action of plant roots, and the effects of organic substances formed by biological activity. 

Soil reaction (pH) The relationship between the environment and development of acid or alkaline conditions in soil has been discussed with respect to formation of soils from the parent rock materials. Soil acidity comes in part by the formation of carbonic acid from carbon dioxide of biological origin and water. Other acidic development may come from acid residues of weathering, shifts in mineral types, loss of alkaline or basic earth elements by leaching, formation of organic or inorganic acids by microbial activity, plant root secretions, and man-made pollution of the soil, especially by industrial wastes. 

Soils that have developed in different environments, or with different parent materials or ages... 

Andisols Andie soil properties (A1 humates, low pH, darkly colored A) Volcanic parent materials... 

Figure 8-5 shows soil orders that form in relation to climate and vegetation along a transect from the poles to the equator along with processes occurring in the soil. In this conceptual diagram, it is assumed that there is a uniform parent material, similar topography and... 

Sediments of Tertiary and Quaternary age, including volcanic ash and aeolian materials, make up the parent material of the soils. In the more arid parts of the Andean System (the coastal plain of Peru and Chile, and the Altiplano of Bolivia) the topography is level. The Altiplano is a very large closed basin with numerous salt flats. In northwestern Argentina, the planar topography is broken by mountains composed of Precambrian rocks and Quaternary sediments. 

The environmental conditions that lead to the formation of a vertic soil structure are also conducive to the formation of suitable parent materials ... 

The primary sources of trace elements in soils are the parent materials from which soils are derived. These parent materials constitute the reserve for trace elements. Concentrations of trace elements in soils are directly dependent upon their abundance in the earth crust. In general, concentrations of most trace elements in global soils are from one third to three times those in the earth s crust. The logarithm ratios of their concentrations in the global soils over the earth s crust are in the range 0.5 (Fig. 2.2). 

Strong correlations occur between concentrations of trace elements in Californian soils. Nickel concentrations in soils are strongly correlated with Cr (r = 0.95) Cu contents are also significantly correlated with Co (r = 0.81). Strong correlations between Ni and Cr and between Cu and Co are observed as well (Marrett et al., 1992). This strong correlation between trace elements indicates that these elements associate in parent materials and suggests similar physical-chemical processes governing soil formation (Bradford et al., 1996). 

Northern Californian soils have higher concentrations of Cr, Co, Cu and Ni than southern California since there are volcanic ultramafic rocks in northern California. Ultramafic rocks are mostly serpentine, a magnesium silicate with associated high amounts of Ni and Cr. Soils formed on serpentine parent materials contain high to extremely high Ni and Cr concentrations in soils. Soil parent material is a factor mostly controlling trace element concentrations in soils. 

Selenium deficiency in humans occurs in the loessial region of the North China and Tibet Plateau of China (Liu, 1996). The arid and semi-arid soils in these areas of China contain low total Se in their parent materials. 

Seleniferous formations occur in the Great Plains region from Canada to Mexico, accounting for > 700,000 km2 of the western U.S. Seleniferous soils are frequently associated with Se-containing geological formations (Boon, 1989). As discussed above, seleniferous formations occur in North Dakota, South Dakota, Montana, Wyoming, Colorado, Kansas, and New Mexico. Some soils derived from Se-rich parent materials, such as Cretaceous shales of the middle-western United States, have > 10 mg/kg Se and sometimes exceed 50 mg/kg (Reeves and Baker, 2000). 

Pettry D.E., Switzer R.E. Arsenic concentrations in selected soils and parent materials in Mississippi. Mississippi State University Mississippi State, MS 39762, USA. 2000. 

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