Subsoil

Sodium is an indispensable element for some crops (notably sugar beet), can partially substitute for potassium in several crops, contributes to neutralising soil and subsoil acidity, and has a positive effect on soil phosphoms solubiUty. Sodium is an essential nutrient for cattle, and sodium appHcation to soil increases its content in pastures. Sodium nitrate is particularly effective as a nitrogen source for sugar beet, vegetable crops, tobacco, and cotton (qv), and for any crop in acid soils. 

The final composition of stream water is the product of the weathering reactions and related processes outlined above. However, the chemical processes are influenced and controlled by an intricate combination of environmental factors that are characteristic for each drainage system. Therefore, the composition of the bedrock in an area and the residual material left at the surface as soil and subsoil exert a strong influence on the chemical composition of mnoff from the area. The reactions of water with this material are the ultimate geological control and are the source of soluble weathering products. 

This is an average value of metal erosion during the length of service and may vary with soil conditions. In coastal areas, for instance, where the subsoil water is saline, erosion of metal would be much more rapid and a further safety factor must be considered. Field experience will be a better guide to assess this. 

While the homestead theory was never seriously considered in the United States experience, it has been recommended as part ot a subsoil privatization program for Latin America. The major attraction is increased economic efficiency Production and management of a contiguous oil and gas resei voir is most efficiently done by one operator, and homesteading creates one owner in place of multiple owners under the rule of capture. 

The discharge of surface water from a site may originate from three potential sources rainwater from building(s), surface-water runoff from paved/hard standing areas and subsoil drainage (groundwater)... 

A levy by the owner of the subsoil or by the state on the value of gas produced, frequently expressed as a percentage of well-head value. 

Drought stress increases the soil mechanical impedance on plant roots, which in turn can stimulate root exudation (1,4,5). lncrea.sed release of mucilage may contribute to the maintainance of Zn uptake in dry soils by facilitating Zn transport to the root surface in mucilage-embedded soil particles (264). This effect might be supported by water transfer from the subsoil in the roots, which is... 

Grass roots can grow and absorb water down to 1 m, or deeper if soil structure is good, although subsoil water is usually poorer in nutrients than topsoil water (Frame, 1992). Transpiration is highest... 

Final cover systems are another important component of waste containment systems used at landfills. While liner systems are installed beneath the waste, final cover (or closure) systems are installed over the completed solid waste mass. For hazardous waste landfills, 40 CFR 264 requires that the landfill be closed with a final cover system that meets certain performance criteria, most notably, that they have a permeability less than or equal to the permeability of any bottom liner system or natural subsoils present. U.S. EPA guidance documents517 recommend that final cover systems for hazardous waste landfills consist of at least the following, from top to bottom ... 

Boer G, Schlett C, Tnier H-P (1993) Substituted anilines Gas chromatographic determination and behaviour during a simulated subsoil passage. Vom Wasser 80 59-63... 

There are many miscellaneous applications of explosives which may be mentioned but which do not merit individual description. Such uses are those in agriculture, in the preparation of ditches, the diversion of streams, removal of tree stumps, and the breaking up of subsoil. Demolition of old buildings and chimneys is readily carried out. Underwater wrecks may also be broken up for disposal by special application of explosive charges. 

Normally, clay in soil is not present as individual particles but is clustered to aggregates that consist wholly of clay or of a mixture of clay and other mineral and/or organic soil material. Mass transport of soil material along cracks and pores, common in cracking soils in regions with alternating wet and dry periods, does not necessarily enrich the subsoil horizons with clay. 

Cavallaro and McBride (1984a) observed that the removal of Fe oxides from two clay soils reduced Zn adsorption. Shuman (1976) reported that the removal of Fe oxides resulted in an increase or decrease in Zn adsorption, but later in another similar study (1988) he found that the removal of either amorphous or crystalline Fe oxides increased Zn adsorption capacity and decreased Zn-bonding energy. The author explained that adsorption sites on the Fe oxide coatings were not as numerous as those released when the coatings were removed. Elliott et al. (1986) observed that DCB extraction of Fe oxides from two subsoils of the Atlantic Coastal Plain increased heavy metal adsorption. Wu et al. (1999) found that Cu adsorption on the fine clay fraction increased after dithionite treatment with possible exposure of much more high-affinity sites for Cu on the fine clay. 

In silt clay soils (0-30 cm) of Isfahan, Central Iran, the amount of EDTA-extractable Zn, Cu, Pb, Ni, Cd, Co and Cr were 3.2, 1.8, 2.6, 0.6, 0.16, 0.6 and 0.8 mg/kg, respectively (Khoshgoftarmanesh and Kalbasi, 2002). Concentrations of these trace elements increased in subsoils (30-60 cm) and increased with applications of municipal waste leachate. In the surface soils of agricultural, industrial and urban regions of Isfahan, central Iran, the average DTPA-Cd was 0.09 mg/kg, and about 80% of the soil samples had less than 0.1 mg/kg DTPA-extractable Cd (Amini et al., 2005). DTPA-Cd was strongly correlated with EC in the soils. 

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