Andosol

Andosol (from Japanese an do , 'dark soil' and Latin solum , 'soil') is one of the 32 reference soil groups of the World Reference Base for Soil Resources (WRB). The group mainly includes soils that have arisen from the ashes of volcanoes . Under acidic weathering conditions, andosols in humid and semi-humid climatic conditions can also be formed from other raw materials that are rich in silicates , such as rocks with a high proportion of clay minerals or weathering coverings from ferralitic weathering .

Delimitation and definition

Andosols according to the WRB classification partly correspond to the andisols , one of the twelve orders of the USDA Soil Taxonomy . In the Japanese system, the Kuroboku soil type is similarly defined; in the French system, comparable soils are also called Andosol or Vitrisol .

Characteristic soil horizons

Soil profile of an Andosol

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

• Subsoil horizon with clay enrichment ( argic )
• horizon dominated by kaolinite and oxides ( ferralic )
• iron-rich soil horizon with a proportion of iron oxide concretions of at least 15% ( plinthic )
• iron-rich soil horizon with a proportion of hardened iron oxide concretions of at least 40% ( pisoplinthic )
• iron-rich soil horizon with continuous hardening ( petroplinthic )
• Illuvial horizon with aluminum as well as iron and / or amorphous organic material ( spodic ).

Additionally must have the andic or vitric properties

• begin at a depth of no more than 25 cm and reach a total thickness of at least 30 cm within one meter

or

• occupy at least 60% of the soil thickness above a hardened layer or the bedrock.

The andic properties

The andic properties are defined in the WRB as follows:

• at least two percent (Al _ox + ½Fe _ox ) content (see below)
• less than 0.9 kg / dm ³ storage density
• at least 85 percent phosphate retention capacity.

It is Al _ox and Fe _ox of aluminum - and iron content in the acidic oxalate - extract as a percentage of the dried at 105 ° C fine soil (0-2 mm).

The andic properties can be further subdivided into silandic and aluandic depending on the silicon and aluminum content .

The vitric properties

The vitric properties are defined in the WRB as follows:

• volcanic glasses with a proportion of at least 5% in the fraction 0.02 - 2 mm (based on the number of soil particles)
• at least 0.4% (Al _ox + ½ Fe _ox ) content
• at least 25 percent phosphate retention capacity.

properties

The soils are characterized by their brown to pitch black color, mostly with a coarser grain size . The loose soil structure leads to rapid weathering and the formation of organo-mineral complexes or minerals such as allophanes , ferrihydrites and imogolites under moist conditions .

An Andosol can reach a thickness of several meters and contain characteristic soil horizons . The fulvic horizon (Latin: fulvus , 'dark yellow') is a dark, more than 30 cm thick soil horizon, the organic part of which is characterized by the predominance of fulvic acids over humic acids . The melanic horizon ( Greek melas , 'black') is a total more than 30 cm thick, dark to black soil horizon, the organic portion of which is characterized by a low ratio of fulvic acids to humic acids.

Andosols are very fertile and easily rootable; very different types of vegetation develop on them . They are mostly used intensively for agriculture and are easy to work with, but due to their high water absorption, they tend to stick in high humidity and are then poorly resilient. For example, sugar cane , tobacco , tea or vegetables are grown, and rice is also grown if the groundwater is close to the surface . The often typical low availability of phosphates is counteracted by adding lime or phosphate fertilizers .

Occurrence

Andosols develop in hilly or mountainous regions, mostly rainy regions, preferably in areas where volcanic ash and comparable products of volcanoes occur. Accordingly, they occur from the polar regions to the tropics . They are often in the area of ​​the Circumpacific Fire Belt and on the Pacific Islands, such as Hawaii , Fiji or Samoa . In Europe, andosols are found in volcanic areas in France , Italy and Germany, as well as on Iceland .

Web links

• Profile photos (with classification) WRB homepage
• Profile photos (with classification) IUSS World of Soils

literature

• IUSS Working Group WRB: World Reference Base for Soil Resources 2014, Update 2015. World Soil Resources Reports 106, FAO, Rome 2015. ISBN 978-92-5-108369-7 ( PDF 2.3 MB).
• W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the world. 2nd Edition. Springer Spectrum, Heidelberg 2014. ISBN 978-3-642-36574-4 .
• W. Amelung, H.-P. Blume , H. Fleige, R. Horn, E. Kandeler , I. Kögel-Knabner , R. Kretschmar, K. Stahr , B.-M. Wilke: Scheffer / Schachtschabel textbook of soil science. 17th edition. Heidelberg 2018. ISBN 978-3-662-55870-6 .
• Soil Survey Staff: Keys to Soil Taxonomy. 12th edition. Natural Resources Conservation Service. US Department of Agriculture. Washington DC, USA, 2014.