Pedogenesis

The pedogenesis, or soil formation is the process of formation of soils. In the course of soil development is the formation and change of soil horizons and their sequences, the soil profiles. We call this process as profile differentiation, because the soil profiles with their development become more complex in general.

The concept of soil development comprises the processes of soil formation and how it fits into a general framework. Typical stages of soil development are classified in soil science as soil types.

  • 4.1 Temporal development series ( chronosequences )
  • Scenic 4.2 development series (relief sequences)
  • 4.3 Climatic developmental series (climate sequences)

Factors of soil formation

General five factors can be distinguished in soil science, from whose influence resulted soil formation. This despite different weighting all factors come into play at the same time:

  • The climate plays a central role, because many soil types are strongly bound in their distribution of climates. Play key roles while the precipitation ( water balance) and the temperature one, which affect the intensity of chemical, biological and physical processes in the soil.
  • Living organisms ( flora and fauna) take by their activity on and in the gray floor a decisive influence, because only through them results in the formation of humus. In addition, they are also involved in the formation of peat bogs or in the mixing of the soil material ( earthworms, etc. ) play a role. Soil bacteria assist in the formation of fertile soils not only as decomposers of plant biomass. The cell envelopes of dead bacteria remain in the soil. They form on mineral soil components an organic film, which contributes significantly to the ground as the crystallization of education.
  • The relief is especially critical for the intensity of erosion. While very old form, deep soils in the Great Plains, prevail on slopes and flat ground, young. In addition, it influences the course of rivers and lakes or the position of the groundwater ( alluvial soils, groundwater soils etc.).
  • The starting material determined by its grain size and chemical composition of many properties of the soil such as pH, nutrient content or the water storage capacity decisively. The result under the same conditions on sandy soil than on a very different tone.
  • The influence of time can be viewed as an overriding factor for the development of a soil is never complete. The older a soil is, the greater the difference between its properties from those of the starting material, and the stronger is its weathering. This is evident, for example, in Germany in the differences between the old and Jungmoränen.

These five factors are according to the English terms ( climate, organics, relief, parent material and time) also referred to as clorpt concept.

For some time, the influence of man is regarded as the sixth factor in addition to these five factors. Due to human activities soils are affected by civil engineering projects, erosion acceleration, soil preparation or supply of technogenic materials like garbage now worldwide.

The following table shows typical examples in which a soil type is dominated by a factor of soil formation.

CryoSol

Terra rossa

Black earth

Tundra, high mountains

Mediterranean climate

Steppenklimate

Alluvial soils

Gleye

Broad river valleys

Sinks with high water table

Pelosol

High clay content

Regosol

Very young site on sand

Plagge floor

Reduktosol

Soil after fertilization Plagge

Landfills

Processes of soil formation

The following processes of soil formation different soil formation factors are involved. This transformation between ( material change ) and translocation ( spatial variation ) are distinguished.

Transformation

The processes of material change in the soil never stand alone. It is rather constructive and degradative processes that work against each other.

  • Mining and construction minerals: General outweighs the decay ( weathering ), ie the crushing of raw material by physical influences such as frost shattering or chemical processes such as the weathering solution. Therefore soils weather increasingly with time, causing very old soils are infertile as a comparatively younger. Effects of weathering include soil acidification, brunification and Verlehmung or Rubefizierung. In addition, always form in the soil and to a lesser extent new minerals.
  • Mining and construction of soil organic matter: In young, poorly developed soils outweighs the humus accumulation ( humification ), so that the levels rise. The organic matter in the soil is degraded also resistant ( mineralization). The older a site is, the more the same in both processes. In the long run equilibrium is reached.
  • The erection and dismantling of soil structure: Describes the physical and biological processes that lead to structure formation ( aggregation ) or resolution ( segregation) lead. Typical processes here are shrinking and swelling of the swellable clay minerals, bonding by polysaccharides in the gut passage of the earthworm or the structure destruction by sodium ions.

Translocation

In the translocation go substances in solution ( mobilization) and then modify its position.

  • Shift: In general, there is a vertical displacement within the soil profile. In humid regions, the substances from the topsoil to be shifted from seepage into deeper areas where they settle again. Of particular importance are the clay translocation ( Lessivierung ) and the combined displacement of soil organic matter and sesquioxides ( podsolization ). In the subsoil subsequently form enrichment horizons of clay or humus and sesquioxides. A horizontal displacement occurs when solutes down the slope failures again. In this way, for example, be transmitted iron accumulates from higher regions in sinks at ( bog iron ). In dry regions, it can also lead to a rise of ground water due to the high evaporation. Here, substances accumulate not in the subsoil, but on the surface, which can lead to Versalzungsproblemen. The accumulation of lime can also occur in arid regions ( carbonation ) and lead to hardening in the underground.
  • Especially iron is displaced very engräumig by differences in redox potential under very wet conditions. This process is called Vergleyung ( groundwater soils ) or Pseudovergleyung ( waterlogging soils).
  • Leaching: This term is used when substances from the soil profile reaching groundwater and not precipitate again, be so removed. In humid regions, where precipitation exceeds evaporation, leaching, and thus this is an essential characteristic depletion of the soil. Depending on the substance different names are selected as nutrient discharge or descaling. In particular, the acidification is often associated with the Kalkverlust. The final stage of leaching is achieved only in the intensive weathering tropics. At the end of soil development, even the silicates leached ( desilication ), so that only the most stubborn iron and aluminum components remain ( Ferrallitisierung ).

Importance for soil description

Mostly genetic soil classification as the German soil classification based on the classification of soil types on the ( completed in the past) soil formation processes. They are often very precise, but require a high basic knowledge of soils ahead and are difficult to understand for the layman. Mostly diagnostic soil classifications such as the U.S. system based almost entirely on existing features. They can therefore be used without any knowledge of soil genesis. In some systems, such as the international soil analysis WRB both genetic and diagnostic features are used.

Soil development series

If the soil-forming factors and processes are known, it can be decided which soil types are suitable and that there are most likely after careful consideration of a site even without close examination. Since the factors climate, relief, starting material and time allow only certain developments in combination of soil development sequences ( sequences) is spoken. In certain regions always get the same soils (soil association ).

Temporal evolution series ( chronosequences )

Under certain climatic conditions make soil on different starting materials always a comparable development through, are the Klimaxböden at the end. In them still run from soil-forming processes, but these only lead to a deepening of the features and not for conversion to other soil types. The following are some chronosequences to be listed schematically, which are typical for Central Europe:

Sandstone: rock Syrosem → → → Ranker brown earth → Parabraunerde → podzol

Sand: Sand Lockersyrosem → → → regosol brown earth → Parabraunerde → podzol

Limestone ( clayey ): rock Syrosem → → → rendzina Terra fusca

Mudstone ( low lime ): rock Syrosem → → → Ranker Pelosol → Pseudogley

Loess ( marly ): Loess Lockersyrosem → → → Pararendzina brown soil ( moist ) or black soil ( dry ) → Parabraunerde → → Podsol Pseudogley

Marine sediments: W → → Rohmarsch Kalkmarsch → march → Klei Altmarschböden as buckling march, Dwogmarsch or Organomarsch

Scenic developmental series (relief sequences)

In Central Europe can be found depending on the landscape typical floors.

Altmoränen landscape

  • Proximity: Plagge Esch (Northern Germany )
  • Sander: podzol
  • Glacial sand: brown soil ( nutrient )
  • Lower: Gley

River landscapes of meadows

  • Headwaters: Rambla
  • Middle course: Paternia and Kalkpaterina
  • Underflow: Tschernitza and Vega

In increasing distance to the river Gley and fen

Cuesta landscape of the highlands

  • Ridge: older, more developed soils as Pelosol ( mudstone ), brown earth (sandstone, marl ) or Terra fusca (limestone)
  • Suspension: young, low soil as powerful Ranker (sandstone, mudstone ), Pararendzina ( marl ) or rendzina (limestone).
  • Foot of the slope: colluvium ( deposits by erosion )

Marine sediments ( marsh ):

  • Foreland: Watt and Rohmarsch
  • Young Marsh: Kalkmarsch and clothing march
  • Altmarschen: Articulated march and Dwogmarsch
  • Geestrand: Organomarsch

Climatic developmental series (climate sequences)

Although the climate in Central Europe as a whole is quite similar, small-scale influences are also traceable to the soil development.

An example is the soil development in the German flare landscapes. The local soils developed on loess, which was blown in during the last ice age the low mountain ranges. You are still so young that they have not reached their climax ( Pseudogley ). The more humid it is down to the west, the farther they have developed.

  • Cologne basin (720 mm): Parabraunerde
  • Hildesheimer Borde (660 mm): ( black earth ) Parabraunerde
  • Magdeburg (600 mm): ( Luvisols ) and black earth
  • Rain shadow area of the resin ( 450 mm ): Black Earth

As another example, the formation of podzols ( climax on sand ) can be called. In the rainy northwest Germany the podsolization is already well advanced. On the east it is much drier. There are at the same age sands reinforced before Cambisols.

Pictures of Pedogenesis

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