Soil horizon

Soil horizon difficulty (see bottom layer), often used in the short form horizon, is a term used in soil science. He refers to a region in the ground with almost the same properties as provided by overlying or less following horizons therefore different areas. The horizons of a soil are at a so-called soil profile ( vertical cross section of the soil in an excavation, a rare hole) recognizable and almost always horizontal or parallel to the slope. The horizon sequence of a soil is the decisive criterion for the determination of this soil type.

Horizons can now be traced layers. Nevertheless, there is a clear demarcation between the two concepts: A layer refers not only to a change in the properties, but also a change of the material ( eg sand to clay ). It is the result of sedimentation (see also geology, physical geography ) or human material relocation.

Definition

Soil horizons are areas within the soil that hold uniformly similar characteristics and properties and differ from overlying or below the following areas. Affect the processes of soil formation and development ( pedogenesis ), or penetrate the soil generally vertically from top to bottom. These are mainly natural processes ie physical or chemical weathering ( by exposure to heat, cold, precipitation ), biological activity ( plant roots, soil organisms, burrowing animals, microorganisms ) or A - or leaching of substances with the precipitation and leachate. In populated regions now also takes the man a big impact (soil rearrangement material entry, plowing ... ).

The horizon sequence

The soil-forming processes are not equally pronounced in the soil. Many of them focus on the surface. This is, for example, overgrown ( humus ), better ventilation (activity of soil organisms ) or exposed to the elements ( weathering ). Humidity regions show a consistent shift of substances from top to bottom, as the rainfall seep. Thus, there are vertical gradient of the bottom-forming processes, and their products, leading to a vertical sequence of the embossed areas in the soil therethrough. Therefore horizons are by nature always more or less above the other, but not next to each other.

The number of horizons can vary significantly from site to site. In a straight up blew sand dune it is 1, because only " pure sand " is present. After a short time it comes to the settlement of pioneer plants and the formation of humus. Thus, the horizon increases to 2, because on the surface, unlike the underground " pure sand " created a range of " sand with humus ". It is thus clear that the horizon sequence is not fixed, but varies with time progressing soil development.

The sequence of soil horizons is so characteristic of the previously elapsed soil development. At their all important soil chemical and biological processes and properties can be read (humus formation and incorporation, acidification, reducing and oxidizing conditions, ...). The approach and interpretation of the available soil horizons is therefore essential component of soil mapping, eg in the context of forestry site investigation when deciding on the appropriate choice of tree species or determining the number of fields. With them, the systematic classification of soils is made in soil types.

Differentiation of soil horizons

Soil horizons (horizon symbols) named with letter combinations that characterize essential features and processes.

The soil horizons can be - in the soil profile from top to bottom - roughly divided as follows:

• H, L, O-horizons: organic surface layer

• A horizons: mineral surface

• B- horizons of mineral soil

• C- horizons of mineral subsoil

The detailed characterization is done by added, trailing lowercase. There are also other prefix letters for special processes and properties that are not caused by soil formation. If more than one pedogenetischer processes that shape a horizon occurrence, other combinations of symbols are formed according to certain rules. The following list and description names the most important horizons and is based on the German soil classification (see Soil Mapping ).

Organic soil horizons

You own a share of more than 30% by mass ( = 60 vol - %) of organic matter.

• H - Peat: Organic horizon of residues torfbildender plants emerged at the surface. The degradation is inhibited by water, it creates peat. A further differentiation by Torfart is possible: nH - ​​from fen
• HH - from peat

• Of - in addition to plant remains occur 10-70 vol - on % organic fine substance as a result of the decomposition (fermentation).
• Oh - the fine organic matter ( humus) as a result of degradation processes outweighs strong.
• O / C soils

Mineral soil horizons

Proportion of organic matter below 30 % by mass

• A horizons Aa - by waterlogging humus accumulation 15 to 30 mass% ( anmooriger topsoil )
• Ae - bleaching, leaching ( Auswaschungshorizont ) of humic substances and iron ( eluvial, typical of podzolic )
• Ah - enrichment of humus (<15 mass%, humus)
• Ai - only slightly powerful accumulation of organic matter (initial)
• Al - leaching of clay particles ( clay translocation = Lessivierung, typical of Luvisols )
• Ap - regular agricultural processing ( plow ) - Topsoil

• B- horizons Bh - accumulation of humic substances is washed (! Strong staining ) and to a lesser extent of sesquioxides, (typical of podzols, see hardpan )
• Bs - accumulation of sesquioxides is washed (iron, manganese and aluminum compounds ) (typical of podzols, see hardpan )
• Bt - eingewaschenem accumulation of clay ( Tonanreicherung, typical of Luvisols )
• Bv - iron oxidation, mineral formation ( brunification, Verlehmung, typical of brown soil )

• C- horizons Cn - non wittertes parent material of soil formation, loose or hard rock ( or novus new)
• IC - C horizon of loose, unconsolidated rock grabbarem ( loess, sand, gravel, etc.)
• MC - C horizon of solid hard rock

More mineral soil horizons

• G - mineral soil horizons with groundwater influence (typical of Gley ) Go - oxidized temporarily groundwater fulfilled, temporarily ventilated, therefore rust spots as a result of oxidation processes
• Gr - usually ground water met, barely ventilated, reducing conditions, predominantly gray as a result of iron reduction

• Sw - storage aquifer, temporary air arm (water- conducting)
• SD - backwater sole, largely impermeable, so that there is too much slower infiltration

Subhydrische soil horizons

• F - horizon on a body of water with usually more than 1 % by mass of organic matter

Soil in the tropical rainforest

In the tropical rainforest chemical weathering dominates due to high temperatures and heavy rainfall. The parent rock is therefore often resolved deep, hence the C horizon is often at depths of 20 to 100 meters. In addition, there were hardly any climatic changes and therefore the weathering could have a very long and so very powerful and profound weathering ceiling emerged since the Tertiary.