Oxygen content of soils

Two bioassays are employed to evaluate the effect of samples on terrestrial life forms. For gas samples, the plant stress ethylene test is presently recommended. This test is based on the well-known plant response to environmental stress release of elevated levels of ethylene (under normal conditions plants produce low levels of ethylene). The test is designed to expose plants to various levels of gaseous effluents under controlled conditions. The ethylene released during a set time period is then measured by gas chromatography to determine toxicity of the effluent. For liquid and solid samples, a soil microcosm test is employed. The sample is introduced on the surface of a 5 cm diameter by 5 cm deep plug of soil obtained from a representative ecosystem. Evolution of carbon dioxide, transport of calcium, and dissolved oxygen content of the leachate are the primary quantifying parameters. 

This process consumes oxygen and produces C02. As a result, the oxygen content of air in soil may be as low as 15%, and the carbon dioxide content may be several percent. Thus, the decay of organic matter in soil increases the equilibrium level of dissolved C02 in groundwater. This lowers the pH and contributes to weathering of carbonate minerals, particularly calcium carbonate. 

The position of the water table determines the oxygen transport and hence the corrosion rate. The moisture content of soil greater than 20% is deemed to be corrosive (general corrosion of carbon steel) and the value of less than 20% was conducive to pitting corrosion.15 This observation is thought to be related to the diffusion rate of oxygen.16 The general effect of soil resistivity on the corrosivity may be denoted as ... 

Factors that must be considered in evaluating the biodegradability of organic wastes in a landfilling application include ( ) composition of the waste (2) compatibility of wastes and soil microflora (3) environmental requirements including oxygen, temperature, pH, and inorganic nutrients and (4) moisture content of soil-waste mixture. 

Oxygen and carbon dioxide content of soil under cacao. Rivers Estate, Trinidad (Russell, 1973)... 

Oxygen content of the soil has no effect on anabolic nitrate reduction, as aerobes use nitrate as nutrient source and reduce it to ammonia during cell synthesis. The assimilative nitrate reductases are soluble proteins and are repressed by high ammonia levels. 

Results from other studies support the rapid degradation of methyl parathion in soils with a high water (i.e., low oxygen) content (Adhya et al. 1981, 1987 Brahmaprakash et al. 1987). Experiments in flooded and nonflooded soils showed that the redox potential affected both the rate of degradation and the transformation products of methyl parathion (Adhya et al. 1981, 1987). Transformation to volatile products was suggested by Brahmaprakash et al. (1987) as the reason that significant amounts of " C from labeled methyl parathion could not be accounted for, especially in flooded soils. 

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