Soil-forming processes

As a result of weathering reactions presented in the above section, it is apparent that ions, molecules, and compounds are either mobilized and removed from the weathering environment or are insoluble, and are retained and eventually accumulate. 

The retention or removal of ions, molecules, and compounds in the weathering and soil environment depends on the nature, strength, and abundance of the proton donors. The biota directly or indirectly affects the production of the proton donors. 

Inorganic and organic proton donors are limited, although chemical weathering does occur (Claridge 1965 Ugolini and Jackson, 1982 Claridge and Campbell, 1984). Mica is altered to vermiculite and 

In the virtual absence of percolating water, salts liberated through weathering or accreted by meteoric input are removed slowly. Consequently, chlorides, sulfates, nitrates, and other soluble salts are retained in the soil. Soils formed in this environment are called Entisols (Soil Survey Staff, 1975 Fig. 

The tundra region stretches south of the polar desert to the margin of the tree line. Precipitation and 

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Fig. 8-5 Soil and soil forming processes - a global view. The moisture and temperature regimes are generalized and intended only to show major pedoclimatic environments. Spodosols, for example, can also occur in a cryic regime and even in equatorial regions. Other orders could also occur in more than one moisture and temperature environment. (overleaf)...

The formation of characteristic structural aggregates vertic structure ) is an additional soil forming process in Vertisols. This typical structure may occur in most of the solum but has its strongest expression in the vertic horizon the grade of development and the sizes of peds change only gradually with depth. 

Much of the Hgt pool was found in the upper part of the soil, which is rich in organic matter. This pattern is likely due to an elevated atmospheric deposition of Hgt over the extended period and immobilization of mercury by organic functional groups and accumulation of organic matter as part of the soil-forming process. The retention of mercury in the mor humus layer was almost complete due to the very strong association between Hgt and humic substances. 

Entisols show no evidence of soil-forming processes leading to profile development Aquents (Gleysols, pt Fluvisols, pt) are formed in continuously or near-continuously wet environments Fluvents (Fluvisols, pt) in recent alluvium in areas that are frequently flooded by rivers depositing new sediment... 

Brinkman R. 1970. Ferrolysis, a hydromorphic soil forming process. Geoderma 3 199-206. 

Genetic soil formed by the soil-forming processes. Horizons of illuviation, residual ... 

Parton, W. J., Schimel, D. S., Ojima, D. S., and Cole, C. V. (1994). A general model for soil organic carbon dynamics Sensitivity to litter chemistry, texture and management. In Quantitative Modelling of Soil Forming Processes, Bryant, R. B., ed., Soil Science Society of America, Madison, WI, pp. 147-168. 

Soils may be developed on either residual or transported material, but irrespective of which is involved, a soil may always be traced back to the parent rocks from which it has formed. This means that all of the minerals that occur in rocks may also occur in soils, in addition to those formed by pedogenic (i.e., soil-forming) processes. There are thousands of different minerals, but the main minerals and groups of minerals encountered in most soils form a much smaller set, numbering around twenty or thirty common types (Table 11.1). 

Podzolization soil-forming process that commonly results in the formation of humic acids and leaching of acids. 

The background site must be of similar characteristics, that is, same topographical location, similar soil physical characteristics, similar water regimen, and similar parent material and soil forming process. 

Fig. 4.13 Flow diagram summarizing soil-forming processes, inputs and outputs. Note that vegetation is influenced by parent material as well as climate.

Figure 3. Soil and soil-forming processes a global view (after Ugolini and Spaltenstein, 1992).

As discussed in Chapter 5, natural soil-forming processes of humid climates tend to acidify soils over the long term. However, in arid climates, because salts are not frequently leached from the soil by rainfall, salts and alkahnity tend to accumulate. This is because the potential evaporation and transpiration of water at the soil surface exceeds rainfall so that the net movement of water is upward in the soil profile. Consequently, salts accumulate at or near the surface of these arid-region soils. However, in localized cases, accumulation of salts and alkalinity arises from confinement, created by a physical barrier to water flow out of a depression in the landscape. Thus, salt problems are not restricted to soils of arid climates. 

The pedosphere is the envelope of the Earth where soils occur and where the soil-forming processes are active. Soils are physical entities formed at the Earth s surface that have acquired chemical and physical properties in response to environmental factors. This concept of soils was introduced by Dokuchaev, a Russian scientist at the end of the last century 0offe, 1949). 

C - unconsolidated material underlying the solum (A and B). It may or may not be made of the same parent material from which the solum formed. It is the least weathered and also little affected by the soil-forming process, although it may be weathered R - underlying consolidated rock... 

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