Formation of soils

Soil formation is influenced by geological (G), environmental (E) and biological (B) factors such that the product, soil (S), is a function of all of these factors with respect to time (t), i.e.  

In fact a number of key factors can be identified in soil formation, including parent material (p), climate (cl), relief (r), vegetation (v) and the influence of organisms (o). Thus, equation 4.15 above can be more precisely written  

The key factors in equation 4.16 are summarized in Fig. 4.13 where the soil is depicted as a simple box. Various inputs and outputs govern the box s content while processes within the box generate the outputs. It is important to note that of all of these factors only time is an independent variable, the others being inextricably linked. For clarity, these factors are discussed individually below, although in nature they operate together. 

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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. 

Soil reaction (pH) The relationship between the environment and development of acid or alkaline conditions in soil has been discussed with respect to formation of soils from the parent rock materials. Soil acidity comes in part by the formation of carbonic acid from carbon dioxide of biological origin and water. Other acidic development may come from acid residues of weathering, shifts in mineral types, loss of alkaline or basic earth elements by leaching, formation of organic or inorganic acids by microbial activity, plant root secretions, and man-made pollution of the soil, especially by industrial wastes. 

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... 

Dec J, K Haider, A Benesi, V Rangaswamy, A Schaffer, E Eernandes, J-M Bollag (1997a) Formation of soil-bound residues of cyprodinil and their plant uptake. J Agric Eood Chem 45 514-520. 

The content of heavy metals in Steppe soils is tightly connected with their contents in geological rocks. In formation of soil exposure pathways in Desert ecosystems, water-soluble forms of these metals play the most important role. We can see an analogy between the increasing content of elements in soil dead organic matter as a function of decreasing water excess in Forest ecosystems and the increasing content of water-soluble species of chemical elements in the soils of Dry Steppe and Desert ecosystems as a function of enhanced aridity. The accumulation of water-soluble species occurs in the upper horizon for almost all elements, with exception of strontium. The main factor responsible for the accumulation of water-soluble forms is connected with evapotranspiration. 

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. 

Dos Anjos, L.H.C. Franzmeier, D.P. Schulze, D.G. (1995) Formation of soils with plinthite on a toposequence in Maranhao State, Brazil. Geoderma 64 257-279... 

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). 

Wang, T. S. C., Kao, M.-M., and Li, S. W. (1978a). A new proposed mechanism of formation of soil humic substance. In Studies and Essays in Commemoration of the Golden Jubilee of Academia Sinica. Academia Sinica, Tapei. Taiwan, pp. 357-372. 

Chaney, K., and Swift, R. S. (1986). Studies on aggregate stability. I. Re-formation of soil... 

Horwath (2007). Carbon cycling and formation of soil organic matter. In Soil Microbiology, Ecology, and Biochemistry, Paul, E. A., ed., Academic Press, Elsevier, Amsterdam, pp. 331. 

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... 

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