The formation of soils

All types of soil derive from the disintegration of rocks and decomposition of vegetation. Disintegration and decomposition were caused by physical and chemical action. The major ones are wind, water, temperature variations and chemical reactions. 

Soils are characterised by the way they were created. They are defined as residual, sedimentary, aeolian and glacial. 

Residual soils are those formed by rocks located just below them. Climatologic conditions (temperature and rainfall) were the main reasons of disintegration of the parent materials. Those soil types consist of inorganic grainy materials, in the form of fine particles in upper layers and in the form of more coarse particles in lower layers. These soils can be used as pavement foundation layer, provided that no drastic chemical disintegration has occurred (tropical climatologic conditions). 

Sedimentary soils are those formed by the deposition of materials that were in suspension in aqueous environments, such as lakes, rivers and oceans. The sedimentary soils vary from clean sand to flocculent clay of marine origin. 

From the sedimentary soils, the alluvial soils are generally suitable as pavement foundation material. 

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Prevention of Soil Crusting. Acid-based fertilizers such as Unocal s N/Furic (a mixture of urea with sulfuric acid), acidic polymers such as FMC s Spersal (a poly(maleic acid) derivative originally developed to treat boiler scale) (58), the anionic polyacrylamides described previously, as weU as lower molecular weight analogues such as Cytec s Aerotil L Soil Conditioner, have all been used successfully in at least some circumstances to prevent the formation of soil cmsts. It is difficult to prove benefits in the laboratory, and field tests may give variable results depending on local weather conditions. 

In contrast, under transport-limited conditions, weathering rates are ultimately limited by the formation of soils that are sufficiently thick or impermeable to restrict free access by water to unweathered material. Erosion rates... 

During dry season, the formation of soil cracks, macro- and micropores is common in the Asian countries with monsoon climate. This process is especially important in... 

Soils develop by the action of the soil forming factors on soil parent materials including material transported by different agents. The result of these soil forming factors is the formation of soil horizons, different colors, and peds. Each of these factors has a pronounced effect on a soil s chemistry. Knowledge of the soil type and profile description can provide the soil chemist, analyst, or researcher with valuable information about the characteristics of soil relevant to the development of extraction, analytical, and instrumental analytical procedures. It also is the place to start when investigating the failure of a procedure. 

Leinweber P, Schulten HR. Differential thermal analysis, thermogravimetry and in-source pyrolysis-mass spectrometry studies on the formation of soil organic matter. Thermochim. Acta 1992 200 151-167. 

Adsorption influences the reactivity of surfaces. It has been shown that the rates of processes such as precipitation (heterogeneous nucleation and surface precipitation), dissolution of minerals (of importance in the weathering of rocks, in the formation of soils and sediments, and in the corrosion of structures and metals), and in the catalysis and photocatalysis of redox processes, are critically dependent on the properties of the surfaces (surface species and their strucutral identity). 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

Fig. 1. onceptuai model for dispersion via groundwater flow after water-deposit interaotion. This model also indioates the formation of soil geoohemioal anomalies from seismic pumping of groundwater. 

Smee, B.W. 1998. A new theory to explain the formation of soil geochemical responses over deeply covered gold mineralization in arid environments. Journal of Geochemical Exploration, 61, 149-172. 

Physical weathering The mechanical breakdown of rocks into smaller fragments, which then contribute to the formation of soils and sediments (compare with chemical weathering and weathering). 

In contrast, under transport-limited conditions, weathering rates are ultimately limited by the formation of soils that are sufficiently thick or impermeable to restrict free access by water to unweathered material. Erosion rates are low, and soils and solid weathering products are cation-deficient. In regions where transport-limited erosion predominates, soils are thick and slopes are slight and convexo-concave (Fig. 6-2b). With time, these... 

FIGURE 1 Major processes, pools, and fluxes involved in the formation of soil organic matter. 

The primary factors that are involved in the formation of soil and that determine its final characteristics are (a) parent materials (b) climate (c) living organisms (plants, animals and microorganisms) (d) topography and (e) time. Marked differences in any one of these factors is likely to have a major effect on the nature of the resulting soil. It is because each of these factors is so important and so interdependent that we have such widely varying types of soils. 

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