Drying of soil

Soil Drying of soil sample followed by sieving digestion with HN03 centrifugation ICP/AES 0.09 pg/g 97-103 Schmitt et al. 1988... 

Olsen, R.C. and Court, M.N. (1 982) Effect of wetting and drying of soils on phosphate adsorption and resin extraction of soil phosphate, youma/ of Soil Science 33, 709-71 7. 

An organic mulch also protects the soil against crust formation, but aside from the scarcity of mulching materials and costs, the use of mulches presents other problems that are discussed in detail in Chapter 25. Many types of mulches, if properly managed (Army et al., 1961), are very effective in minimizing runoff. Plant residues on the surface also markedly decrease the rate of drying of soil in the surface half-inch layer, but under field conditions Army et al. observed that the soil moisture content below 2 inches was not materially increased by surface residues. 

Atmospheric conditions such as wind speed, temperature and relative air humidity are some environmental conditions that influence the volatilization rate. Increased wind speed tends to reduce the resistance to gas phase transport. This has the effect of increasing the dry gaseous deposition flux to the soil, but can also clearly increase the revolatihzation of the chemical from the soil [5, 30]. Temperature has a profound effect on the vapour/soil partitioning. Volatilization rates are influenced by soil and ambient air temperature mainly through its effect on vapour pressure, i.e. increase of temperature increases vapour pressure. If the relative humidity of the air is not 100%, increases in airspeed wiU hasten the drying of soil. This indirect effect alters the soil water content, which as it was previously mentioned has an effect on volatilization [30, 31]. 

A sample of soil can be collected tind taken back to the laboratory for pH analysis. There, the soil can be mixed with distilled water (1 1 by volume), shaken well, and then the pH measured in a sample of the filtered extract solution. In the case of soils rich in sulfide, the pH value could be more acidic because of the oxidation of sulfides to sulfates as the soil dries out. The treatment of the soil prior to pH measurement is still an open issue. Drying of soil samples and addition of distilled water are two of the treatments used. However, the soil resistivity value is not sufficient to unambiguously indicate the soil corrosivity. For example, a neutral soil (pH 6.6-7.3) could be very corrosive due to the presence of chloride ions. Table 7 presents an approximate relationship between pH of soil water extract and soil corrosivity. 

Consider a lake with a smaU watershed in a forest ecosystem. The forest and vegetation can be considered as an acid concentrator. SO2, NO2, and acid aerosol are deposited on vegetation surfaces during dry periods and rainfalls they are washed to the soil floor by low-pH rainwater. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. Aluminum, calcium, magnesium, sodium, and potassium are leached from the soil into surface waters. The ability of soils to tolerate acidic deposition is very dependent on the alkalinity of the soil. The soil structure in the... 

Bulk density, soil - Mass of dry soil per unit bulk volume (combined volume of soil solids and pore space). 

Clay. This material is found at the surface of the earth and often is the major component of soils. The material is plastic when wetted, but becomes hard and brittle when dried and heated. It is composed mainly of hydrous aluminum silicates as well as other minerals. 

Corrosion in soil is aqueous, and the mechanism is electrochemical (see Section 1.4), but the conditions in the soil can range from atmospheric to completely immersed (Sections 2.2 and 2.3). Which conditions prevail depends on the compactness of the soil and the water or moisture content. Moisture retained within a soil under field dry conditions is largely held within the capillaries and pores of the soil. Soil moisture is extremely significant in this connection, and a dry sandy soil will, in general, be less corrosive than a wet clay. 

No corrosion occurs in a completely dry environment. In soil, water is needed for ionisation of the oxidised state at the metal surface. Water is also needed for ionisation of soil electrolytes, thus completing the circuit for flow of a current maintaining corrosive activity. Apart from its participation in the fundamental corrosion process, water markedly influences most of the other factors relating to corrosion in soils. Its role in weathering and soil genesis has already been mentioned. 

Except for zones below the level of permanent ground water where the environment is water-saturated, and for zones of dry surface sand, continual variation may be expected to occur in the water content of soils. This is usually dependent on rainfall, snow, flooding and such climatic influences, though irrigation practices in many agricultural areas influence water content and hence the corrosion rates. 

A soil sample was taken from a field, transported back to the laboratory by road and stored for three weeks prior to analysis. The analytical procedure consisted of drying the soil in an oven at 100°C for 24 h before the analyte was extracted using 200 cm of dichloromethane. This extract was reduced in volume to 200 til and a 20 p.l aliquot then analysed by HPLC. A calibration was set up by measuring the response from a number of solutions containing known concentrations of the analyte. The resnlt obtained from the unknown , after suitable mathematical manipulation, indicated the original soil sample contained 20 0.05 mgkg of the analyte. Comment on the accuracy of this result. 

To enable comparison to this experimental approach, archaeological human bones of various ages and soil properties (Table 9.1) from the Anthropological Collection in Munich were analyzed. All German skeletal series come from humic soil with, neutral to slightly basic pH. The samples from Tinkey, Syria, coastal Pern and Egypt have been buried in dry, sandy soils. Soil samples from most of the excavation sites were available and bone sample... 

Grupe, G. in press Preservation of collagen in bone from dry sandy soil. Journal of Archaeological Science. 

Bridge, B.J., Mott, J.J., Winter, W.H. Hartigan, R.J. (1983). Improvement in soil structure resulting from sown pastures on degraded areas in the dry savanna woodlands of northern Australia. Australian Journal of Soil Research, 21, 83-90. Cionco, R.M. (1972). A wind profile index for canopy flow. Boundary Layer Meteorology, 3, 255-63. 

Blackman, P.G. Davies, W.J. (1985). Root to shoot communication in maize plants of the effects of soil drying. Journal of Experimental Botany, 36, 39-48. 

Sensing of soil drying by the plant root system and the resulting regulation of shoot physiology... 

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