The pedogenesis or bottoming out is the process of formation of soils . In the course of soil development , soil horizons and their sequences, the soil profiles, are formed and changed . This process is also known as profile differentiation, as the soil profiles usually increase in complexity as they develop.
Soil formation factors
In general, five factors are distinguished in soil science, the influence of which results in soil formation. Despite different weighting, all factors always come into play at the same time:
- The climate plays a central role, because the distribution of many types of soil is strongly tied to climate zones. Precipitation ( water balance ) and temperature play a key role here , influencing the intensity of chemical, biological and physical processes in the soil.
- Living beings ( flora and fauna ) take on and have a decisive influence on the soil through their activity, because only through them does humus develop . They also play a role in peat formation in bogs or in the mixing of the soil material ( earthworms etc.). Soil bacteria support the formation of fertile soils not only as decomposers of plant biomass. The cell envelopes of dead bacteria remain in the soil. They form an organic film on mineral soil components which, as a crystallization point, contributes significantly to soil formation.
- The relief is particularly decisive for the intensity of the erosion. While very old, deep soils are formed on large plains, young and shallow soils predominate on slopes. In addition, it influences the course of rivers and lakes or the location of the groundwater ( floodplain soils , groundwater soils , etc.).
- Through its grain size and chemical composition , the raw material has a decisive influence on many properties of the soil, such as the pH value , the nutrient content or the water storage capacity . Thus, under otherwise identical conditions, a completely different soil is created on sand than on clay.
- The influence of time can be seen as an overriding factor because the further development of a floor is never complete. The older a soil is, the more its properties differ from those of the original material and the more it is weathered. This is shown e.g. B. in Germany on the differences between old and young moraines .
These five factors are to the English terms ( cl imate, o rganics, r elief, p arent material and t ime) as clorpt referred concept.
For some time now, in addition to these five factors, human influence has been considered a sixth factor. Human activities are now influencing soils around the world through civil engineering measures, accelerated erosion, soil cultivation or the addition of technogenic materials such as garbage.
The following table shows typical examples in which a soil type is dominated by a soil formation factor.
Decisive factor Soil type Typical conditions / locations Zonal floors climate Ferralsol Always humid tropics Azonal soils Creature Peatland High moors , fens relief shallow soils Slopes
wide river valleys
Depression with a high water table
Source material Podzol low-lime loose material such as sand
high clay contents
time Podzol older location on sand
very young location on sand
Human activity Deep rubble floor Soil after deep plowing
Soil after pest fertilization
Soil formation processes
Various soil formation factors are involved in the following soil formation processes. A distinction is made between transformation (material change) and translocation (spatial change).
The processes of material change in the soil never stand on their own. Rather, it is a matter of constructive and dismantling processes that work against each other.
- Degradation and build-up of minerals: In general, disintegration ( weathering ) predominates , i.e. the comminution of the starting material through physical influences such as frost bursting or chemical processes such as solution weathering . Soils therefore weather increasingly over time, which means that very old soils are less fertile than comparatively younger ones. Effects of weathering include soil acidification , Verbraunung and Verlehmung or Rubefizierung . In addition, however, new minerals are constantly forming in the soil.
- Degradation and build-up of organic soil matter: On young, less developed soils, humus accumulation ( humification ) predominates , so that the content increases. The organic matter in the soil is also constantly degraded ( mineralization ). The older a location gets, the more the two processes become more similar. An equilibrium is reached in the long term.
- Build-up and breakdown of the soil structure : Describes the physical and biological processes that lead to structure formation ( aggregation ) or dissolution ( segregation ). Typical processes here are the shrinking and swelling of swellable clay minerals , sticking through polysaccharides when the earthworm passes through the intestine or the destruction of the structure by sodium ions.
During the translocation, substances go into solution (mobilization) and then change their position.
- Displacement : Usually it is a vertical displacement within the soil profile. In humid regions, the substances from the topsoil are shifted by the seepage water into deeper areas, where they are deposited again. The shifting of clay ( Lessivierung ) and the combined shifting of humus and sesquioxides ( Podsolierung ) are of particular importance . Enrichment horizons of clay or humus and sesquioxides then form in the subsoil. A horizontal shift occurs when dissolved substances precipitate again down the slope . In this way, z. B. iron discharged from higher regions in depressions ( lawn iron stone ). In dry regions, the high level of evaporation can also lead to a rise in groundwater. Here, substances do not accumulate in the subsoil, but on the surface, which can lead to salinization problems. The accumulation of lime can also take place in dry regions ( carbonation ) and lead to hardening in the subsoil.
- Iron, in particular, is shifted very tightly under very wet conditions due to differences in the redox potential . This process is referred to as gleying (groundwater soils) or pseudo-gleying (waterlogged soils) .
- Leaching : This term is used when substances from the soil profile get into the groundwater and do not precipitate again, i.e. are transported away. In humid regions, where precipitation exceeds evaporation, this leaching and thus impoverishment is an essential characteristic of the soil. Depending on the substance, different names are chosen such as nutrient discharge or decalcification . Acidification, in particular, is often associated with loss of lime. The final stage of leaching is only reached in the weather-intensive tropics. At the end of the soil development, even the silicates are washed out ( desilification ), so that only the most stubborn iron and aluminum components remain ( ferrallitization ).
Significance for soil address
Predominantly genetic soil classifications such as the German Soil Systematics are based on the soil formation processes (carried out in the past) when classifying soil types. They are often very precise, but require a high level of basic knowledge about soils and are difficult to understand for laypeople. Predominantly diagnostic soil classifications like the US system are based almost entirely on existing characteristics. They can therefore be used without any knowledge of soil genesis. In some systems, such as the international soil address WRB , both genetic and diagnostic traits are used.
Soil development series
If the soil-forming factors and processes are known, after a closer look at a location, it can be decided without further investigation which soil types are possible and most likely to be present. Since the factors climate, relief, raw material and time in combination only allow certain developments, we speak of soil development series (sequences). The same soils always occur in certain regions (soil association).
Temporal development series (chrono sequences)
Under certain climatic conditions, soils on different raw materials always undergo a comparable development, at the end of which there are climax soils. Soil-forming processes still take place in them, but these only lead to a deepening of the characteristics and no longer to the transformation into other soil types. In the following some chronological sequences are to be listed schematically, which are typical for Central Europe:
Landscape development series (relief sequences)
In Central Europe, typical soils can be found depending on the landscape.
Old moraines landscape
- Close to settlement: Plaggenesch (only Northern Germany)
- Sander : Podzol
- Boulder sand : brown earth (low in nutrients)
- Lower: Gley
River landscapes of the floodplains
- Upper course : Rambla
- Middle reaches : Paternia and Kalkpaterina
- Lower course : Tschernitza and Vega
- Mountain ridges: older, more developed soils such as Pelosol (mudstone), brown earth (sandstone, marlstone ) or terra fusca (limestone)
- Slopes: young, thin soils such as Ranker (sandstone, claystone), Pararendzina (marlstone) or Rendzina (limestone).
- Slope foot: colluvium (deposits from erosion )
Marine sediments ( marshland ):
- Foreland of the dyke : Watt and raw march
- Jungmarschen : Kalkmarsch and Kleimarsch
- Altmarschen : Knickmarsch and Dwogmarsch
- Geestrand: organic march
Climatic development series (climate sequences)
Although the climate in Central Europe is quite similar overall, influences on soil development can also be demonstrated on a small scale.
One example is the soil development in the German Börden landscape . The soils there originated on loess, which was blown in front of the low mountain ranges during the last ice age. They are still so young that they have not reached their climax stage (pseudogley). The wetter it gets to the west, the further they have developed.
- Cologne basin (720 mm): Parabraunerde
- Hildesheimer Börde (660 mm): (Black earth) -Parabraunerde
- Magdeburger Börde (600 mm): (Parabraunerde) black earth
- Rain shadow area of the Harz (450 mm): black earth
Another example is the formation of podsoles (climax stage on sand). Podsolation is already well advanced in rainy north-west Germany . In the far east it is much drier. There are still more brown earths on sands of the same age.
- Ad-Hoc-AG Soil: Soil Science Mapping Instructions (KA5) . 5th edition. E. Schweizerbart'sche Verlagbuchhandlung, Hanover 2005, ISBN 3-510-95920-5 .
- E. Mückenhausen: Soil science . 4th edition. DLG publishing house, Frankfurt a. M. 1993, ISBN 3-7690-0511-2 .
- Hans-Peter Blume: Textbook of soil science (Scheffer / Schachtschabel) . 15th edition. Spectrum Akademischer Verlag, Heidelberg, Berlin 2002, ISBN 3-8274-1324-9 .
- Dead bacteria make soils fertile . www.pflanzeforschung.de. Retrieved January 31, 2013.