Andosols

Andosol (from Japanese to do, black soil ' and the Latin sol, soil ') is one of the 32 Reference Soil Groups of the World Reference Base for Soil Resources ( WRB ). The group mainly comprises soils that have arisen from the ashes of volcanoes. Under acidic weathering conditions Andosols can occur in humid and semi-humid climate conditions also from other raw material, which is rich in silicates, such as loess, rocks with a high content of clay minerals or weathering ceiling of ferralitischen weathering.

Delineation and definition

Andosols according to the WRB classification correspond in part to Andi brines, one of the twelve main groups of the USDA soil classification. In the Japanese system, the soil type of the Kuroboku is similarly defined, in the French system similar soils are also called Andosol or Vitrisol.

Characterizing soil horizons

In the WRB soil classification Andosols are defined as soils with andic or vitric properties (see below), which do not have the following soil horizons within the top half a meter:

  • Clay-rich subsurface horizon ( argic )
  • By rearrangement of aluminum - and iron-rich soil horizon without iron concretions ( ferralic )
  • Iron-rich soil horizon with a share of iron concretions between 15 and 40 % ( plinthic )
  • Iron-rich soil horizon with a share of iron concretions about 40 % ( pisoplinthic )
  • Iron-rich soil horizon with platy, hard iron concretions ( petroplinthic )
  • Illuvial horizon with amorphous organic matter and aluminum or iron ( spodic ).

In addition, they must

  • Beginning at a depth of not more than 25 cm, and achieve an overall thickness of at least 30 cm within a meter

Or

  • Occupy at least 60 % of the floor thickness above a hardened layer or the bedrock.

The andic property

Andic the property is defined in the WRB as follows:

  • At least two percent ( Alox ½ Feox ) content (see below)
  • Most 0.9 kg/dm.sup.3 storage density
  • At least 85 percent phosphate retention
  • Less than 25 percent organic carbon.

This Alox and Feox is the aluminum and iron content in the acid oxalate-extractable percentage of dried at 105 ° C fine earth (0-2 mm).

Andic the property, depending on the silicon and aluminum content in silandic and aluandic further subdivided.

The vitric property

Vitric the property is defined in the WRB as follows:

  • Volcanic glasses with a share of at least 5% in the fraction from 0.05 to 2 mm, or in the fraction from 0.02 to 0.25 mm (based on the number of soil particles )
  • At least 0.4 % ( Alox ½ Feox ) content
  • At least 25 percent phosphate retention
  • Less than 25 percent organic carbon
  • The non-fulfillment of at least one criterion of andic property.

Properties

The soils are characterized by their brown to jet-black stratification, usually with coarser grain size. The loose soil structure leads under humid conditions for the rapid weathering and formation of organo- mineral complexes or minerals such as allophane, Ferrhydriten and Imogoliten.

An Andosol can reach several meters in thickness and contain characteristic soil horizons. The fulvic horizon (Latin fulvus, ' dark yellow) is a dark, in the soil profile a total of more than 30 cm soil horizon powerful, the organic portion is characterized by the predominance of fulvic acids over humic acids. The melanic horizon (from Greek melas, black ' ) is a soil profile a total of more than 30 cm of powerful, dark to black soil horizon that contains aluminum -humus complexes and is characterized by a low ratio of fulvic to humic acids.

Andosols are very fertile and easily durchwurzelbar to them evolve very different vegetation types. They are usually used intensively for agriculture and are easy to work with, however, tend due to their high water absorption capacity under high humidity for bonding and are then poorly resilient. The main crops as sugar cane, tobacco, tea or vegetables in groundwater near the surface lying in Rice. The often typical low availability of phosphates is counteracted by the addition of lime or phosphate fertilizer.

Occurrence

Andosols develop in hilly or mountainous, rain -rich regions, preferably in areas where volcanic ash occur and comparable ejecta from volcanoes. Accordingly, they come from the polar regions to the tropics on. They are often in the area of ​​circumpacific fire belt, and the Pacific Islands, as Hawaii, Fiji or Samoa. In Europe, Andosols found in volcanic regions of France, Italy and Germany as well as in Iceland.

Andisols Aluminium Amorphous solid Kaolinite
61230
de