Moisture content of soil

Two different types of information can be obtained by bombarding soil with neutrons. Fast neutrons are slowed when they interact with water and thus can be used to measure the amount of water present. This type of analysis is most often conducted in the field rather than in the laboratory. Figure 8.2 illustrates the use of a fast neutron source and a slow neutron detector to measure the moisture content of soil. This method depends on the interaction of neutrons with hydrogen and so it is not as useful in soils with significant or highly variable organic matter contents. 

Characteristics of soil Quantity of waste Utility/fuel rates Moisture content of soil Initial contaminant concentration Characteristics of residual waste Waste handling/preprocessing Target contaminant concentration Amount of debris with waste Labor rates... 

Moisture content of soil Site preparation Depth of contamination Depth to ground water... 

Moisture content of soil affects power requirements. The contaminants are not treated in a confined area, so some migration of the materials being treated is possible. This technology has not been field tested for remediation applications. 

Low soil moisture allows bed slipping and sfiding as opposed to tumbling, which promotes agglomeration and agglomerate growth. The moisture content of soil to be treated by this method should be between 15 and 18%. 

Incomplete tables of the physical constants and efficacies of a large number of compounds have been prepared (Table I). However, investigations show that much more information is needed to give a complete understanding of soil fumigation. We need tables showing vapor pressure, aqueous solubility, solvency in or solubility of nemic waxes, and efficacy, for temperatures of 20 , 25 , 30 , 35 , and 40 C. Furthermore, efficacy should be expressed in relation to moisture content of soil and stage of nematode. 

Radioisotopes are widely used in die measurement of process variables, including the level of liquids and solids in tanks, silos, and other vessels, the density and specific gravity of fluids and solids, the thickness of sheets and coatings, the moisture content of soils and other solids, the mass flow of materials in pipelines or on belts, and the determination of chemical composition of raw materials, in-process materials, and end-products. Representative examples of these applications are given in Table 6. 

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. 

The increase of atmospheric CO2 may have decreased the pH of precipitation very slightly, but PcOj in soils is far more important for the acid-base status of surface waters. Variation in forest soil Pco is related to the temperature and moisture content of soils as well as the release of excess soil CO2 to the atmosphere. Warmer conditions increase the rate of microbial and root respiration in the soil, thereby increasing soil Pco above the long-term average value and producing short-term increases in runoff ANC, and vice versa. Norton et al. (2001) found that intra-seasonal variations in Pco caused by variable snowpack thickness could induce variation in ANC in runoff of 10-15 peqL Such variability is comparable to variability in ANC caused by a 15-20 p.eqL change in SO4 in runoff. Decline in soil Pco, despite increased temperature and possibly increased soil respiration could result from a lower soil moisture content and a greater efflux of soil CO2. 

Water is the most important limiting factor for crop production in many areas of the world. The efficient use of water in irrigation systems requires continuous monitoring of the moisture content of soil. Neutron moisture gauges are ideal instruments for this purpose and help soil physicists to make the best use of limited water resources. Through these methods, traditional irrigation methods are improved and in some cases up to 40% of the water can be saved. 

Several radioisotopes are used to ensure safety in industry and transportation. For example, iridium-192 is used to verify the structural integrity of aircraft, ships, bridges, and other structures, for weld inspection, and other purposes. Califomium-252 is used to gauge the moisture content of soil in road construction and the building industries. 

Evidently the ideal sampling depth from the viewpoint of a constant Rn signal is 2 m or more. In practice such a depth is seldom attained because of practical difficulties. Quite often overburden thicknesses are less than 2 m, and as was shown above, variation in depth from site-to-site in near-surface surveys can have a pronounced effect on the soil-gas Rn concentration, apart from any meteorological variations. The meteorological variables responsible for these large changes in the soil-gas Rn concentration are barometric pressure, moisture content of soil, wind, temperature, convection and Earth tremors. 

In his conclusions, Smith also covers some general information, besides the specific tests on mixers and soils of Table VIII. He states that a stationary mixer is preferable to a traveling mixer for treating heavy soils, especially with trace additives and also that variation in consistency and moisture content of soils, plus the presence of occasional large stones, must be handled by a commercial mixer. He also states that precrushing of Boil fed to a mixer with close clearance is needed, and that good control of the feed rates is important. 

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