Podzol

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Podzol
Podsol, Podosol, Spodosol, Espodossolo
Podzol.jpg
The picture is of a stagnic podzol in upland Wales, and shows the typical sequence of organic topsoil with leached grey-white subsoil with iron-rich horizon below. This example has two weak ironpans.
Used in WRB, USDA soil taxonomy, others
WRB codePZ
Profile O(Ah)EBhsC
Key process podzolization
Parent materialquartz rich debris and sediment
Climate humid continental, subarctic, oceanic, equatorial
H: common
O: always, has humified organic matter mixed with minerals
A: absent in most boreal podzols [1]
E: common, is ashen grey and leached in Fe and Al
B: always, receives Fe and Al through illuviation
C: common

In soil science, podzols are the typical soils of coniferous or boreal forests and also the typical soils of eucalypt forests and heathlands in southern Australia. In Western Europe, podzols develop on heathland, which is often a construct of human interference through grazing and burning. In some British moorlands with podzolic soils, cambisols are preserved under Bronze Age barrows. [2]

Contents

Term

Podzol means "under-ash" and is derived from the Russian под (pod) + зола́ (zola); the full form is подзо́листая по́чва (podzolistaya pochva), meaning "under-ashed soil". The term was first given in mid-1875 by Vasily Dokuchaev. [3] [4] It refers to the common experience of Russian peasants of plowing up an apparent under-layer of ash (leached or E horizon) during first plowing of a virgin soil of that type. [5]

Characteristics

Podzols can occur on almost any parent material but generally derive from either quartz-rich sands and sandstone or sedimentary debris from magmatic rocks, provided there is high precipitation. [6] Most Podzols are poor soils for agriculture due to the sandy portion, resulting in a low level of moisture and nutrients. Some are sandy and excessively drained. Others have shallow rooting zones and poor drainage due to subsoil cementation. A low pH further compounds issues, along with phosphate deficiencies and aluminum toxicity. The best agricultural use of Podzols is for grazing, although well-drained loamy types can be very productive for crops if lime and fertilizer are used.

The E horizon (or Ae in Canadian soil classification system), which is usually 4 to 8 centimetres (1.6 to 3.1 in) thick, is low in Fe and Al oxides and humus. It is formed under moist, cool and acidic conditions, especially where the parent material, such as granite or sandstone, is rich in quartz. It is found under a layer of organic material in the process of decomposition, which is usually 5 to 10 centimetres (2.0 to 3.9 in) thick. In the middle, there is often a thin horizon of 0.5 to 1 centimetre (0.2 to 0.4 in). The bleached soil horizon, which always has a higher value than the horizons above and below it, goes over into a red or red-brown horizon (so-called Podzolic B). The colour is strongest in the upper part, and change at a depth of 50 to 100 centimetres (20 to 40 in) progressively to the part of the soil that is mainly not affected by processes; that is the parent material. The soil profiles are designated by the letters A (topsoil), E (eluviated soil), B (subsoil) and C (parent material).

In some Podzols, the E horizon is absent—either masked by biological activity or obliterated by disturbance. Podzols with little or no E horizon development are often classified as brown Podzolic soils, also called Umbrisols or Umbrepts .

Geographic distribution

Distribution of Podzol soils according to the World Reference Base for Soil Resources classification: .mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{} Dominant (more than 50% of soil cover) Codominant (25-50%) Associated (5-25%) Podzol map.svg
Distribution of Podzol soils according to the World Reference Base for Soil Resources classification:
  Dominant (more than 50% of soil cover)
  Codominant (25-50%)
  Associated (5-25%)

Podzols cover about 4,850,000 square kilometres (1,870,000 sq mi) worldwide and are usually found under sclerophyllous woody vegetation. By extent Podzols are most common in temperate and boreal zones of the Northern Hemisphere but they can also be found in other settings including both temperate rainforests and tropical areas. [7]

In South America Podzols occur beneath Nothofagus betuloides forests in Tierra del Fuego. [8]

Podzolization

A Podzol with a characteristic eluvial (bleached, ash-colored) horizon and intensely coloured illuvial horizons. The photo was taken in the Feldberg area, Southern Black Forest, Germany. Eisenhumuspodsol.jpg
A Podzol with a characteristic eluvial (bleached, ash-colored) horizon and intensely coloured illuvial horizons. The photo was taken in the Feldberg area, Southern Black Forest, Germany.

Podzolization (or Podsolization [9] ) is a complex soil formation process by which dissolved organic matter and ions of iron and aluminium, released through weathering of various minerals, form organo-mineral complexes (chelates) and are moved from the upper parts of the soil profile and deposit in the deeper parts of soil. Through this process, the eluvial horizon becomes bleached and of ash-grey colour. The complexes move with percolating water further down to illuviated horizons which are commonly coloured brown, red or black as they accumulate and consist of cemented sesquioxides and/or organic compounds. The podzolization is a typical soil formation process in Podzols. [9] [10]

Preconditions

Podzolization usually occurs under forest or heath vegetation and is common in cool and humid climates as these climates inhibit the activity of soil microbes in the topsoil. Overall, podzolization happens where the decomposition of organic matter is inhibited and as a result, acidic organic surface (mor) layers build up. Under these typically acidic conditions, nutrient deficiency further hampers the microbial degradation of organic complexing agents. [10] [11] Medium to coarse textured soils with base-poor parent material (usually rich in quartz) also promote podzolization, as they encourage percolating water flow. [11] [12]

Key steps

The soil-forming process of podzolization can be broken down into two main steps:

  1. Mobilization and translocation of organic matter, Fe and Al from the surface horizon, and
  2. Immobilization and stabilization of organic matter, Fe and Al into the subsoil. [11] [13] [14]
    Podzol A layers Podzol A soils.svg
    Podzol A layers

In the topsoil of acidic soils, organic matter (mostly from plant litter, the humus layer and root exudates) together with Al- and Fe-ions, form organo-mineral complexes. These soluble chelates then relocate with percolating water from the A (or E horizon) to the B horizon. As a result of this, the E horizon (or Ae horizon in the Canadian system of soil classification) is left bleached and ash-grey in colour, while the B horizon becomes enriched with relocated organo-mineral complexes. The colour of B horizon is consequently red, brown or black, depending on the dominance of metal ions or organic matter. Usually, the boundary between the B and eluvial Ae (or E) horizon is very distinct, and sometimes a hardpan (or Ortstein [12] ) can form, as the relocated Fe and Al and organic matter increase mineral particles, cementing them into this compacted layer. [10] [11] [12]

There are several reasons why these organo-mineral complexes immobilize in the B horizon: If during the eluviation process more Al- or Fe-ions bind to the organic compounds, the complex can flocculate as the solubility of it decreases with increasing metal to carbon ratio. Apart from that, a higher pH (or higher Ca content) in the lower soil horizons can result in the breakdown of metal-humus complexes. In the lower soil layers, the organic complexing agents can be degraded by functioning microorganisms. Already established complexes in the B horizon can act as a filter, as they adsorb the traveling complexes from the upper soil horizons. A decreased water conductivity due to higher clay content can also result in the early flocculation of organo-mineral complexes. [10] [11]

The relocated substances can sometimes separate in the illuvial horizons. Then, organic substances are mostly enriched in the uppermost part of the illuvial horizon, whereas Fe- and Al-oxides are mostly found in the lower parts of the illuvial horizon. [10]

Podzolization also promotes the relocation of some nutrients (Cu, Fe, Mn, Mo and P) that sometimes brings them closer to plant roots. [10]

In different soil classification systems

The definitions in different soil classification systems are quite different. Especially soils that show pronounced other soil-forming processes in addition to podzolization are handled in different ways. The following correlations refer to soils, which have undergone advanced podzolization but lack prominent other soil-forming processes.

The term Podzols is used in the World Reference Base for Soil Resources [15] (WRB) and in many national soil classification systems (in some of them, spelled Podsols).

See also

Related Research Articles

<span class="mw-page-title-main">Humus</span> Organic matter in soils resulting from decay of plant and animal materials

In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground".

<span class="mw-page-title-main">Soil</span> Mixture of organic matter, minerals, gases, liquids, and organisms that together support life

Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.

<span class="mw-page-title-main">Chernozem</span> Soil type; very fertile, black-coloured soil containing a high percentage of humus

Chernozem, also called black soil, regur soil or black cotton soil, is a black-colored soil containing a high percentage of humus and high percentages of phosphorus and ammonia compounds. Chernozem is very fertile soil and can produce high agricultural yields with its high moisture-storage capacity. Chernozems are a Reference Soil Group of the World Reference Base for Soil Resources (WRB)

USDA soil taxonomy (ST) developed by the United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series. The classification was originally developed by Guy Donald Smith, former director of the U.S. Department of Agriculture's soil survey investigations.

<span class="mw-page-title-main">Gelisol</span> Permafrost soils

Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two meters of the soil surface. The word "Gelisol" comes from the Latin gelare meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing characteristic of Gelisols.

A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below.

<span class="mw-page-title-main">World Reference Base for Soil Resources</span> International soil classification system

The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the fourth edition 2022. It is edited by a working group of the International Union of Soil Sciences (IUSS).

This is an index of articles relating to soil.

Claypan is a dense, compact, slowly permeable layer in the subsoil. It has a much higher clay content than the overlying material, from which it is separated by a sharply defined boundary. The dense structure restricts root growth and water infiltration. Therefore, a perched water table might form on top of the claypan. In the Canadian classification system, claypan is defined as a clay-enriched illuvial B (Bt) horizon.

<span class="mw-page-title-main">Subsoil</span> Layer of soil under the topsoil on the surface of the ground

Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and it has a small amount of rocks which are smaller mixed with it. The subsoil is also called B Horizon.

<span class="mw-page-title-main">Brown earth</span> Soil type

Brown earth is a type of soil. Brown earths are mostly located between 35° and 55° north of the Equator. The largest expanses cover western and central Europe, large areas of western and trans-Uralian Russia, the east coast of America and eastern Asia. Here, areas of brown earth soil types are found particularly in Japan, Korea, China, eastern Australia and New Zealand. Brown earths cover 45% of the land in England and Wales. They are common in lowland areas on permeable parent material. The most common vegetation types are deciduous woodland and grassland. Due to the reasonable natural fertility of brown earths, large tracts of deciduous woodland have been cut down and the land is now used for farming. They are normally located in regions with a humid temperate climate. Rainfall totals are moderate, usually below 76 cm per year, and temperatures range from 4 °C in the winter to 18 °C in the summer. They are well-drained fertile soils with a pH of between 5.0 and 6.5.

<span class="mw-page-title-main">Gleysol</span> Saturated soil type

A gleysol or gley soil is a hydric soil that unless drained is saturated with groundwater for long enough to develop a characteristic gleyic colour pattern. The pattern is essentially made up of reddish, brownish, or yellowish colours at surfaces of soil particles and/or in the upper soil horizons mixed with greyish/blueish colours inside the peds and/or deeper in the soil. Gleysols are also known as Gleyzems, meadow soils, Aqu-suborders of Entisols, Inceptisols and Mollisols, or as groundwater soils and hydro-morphic soils.

Brown podzolic soils are a subdivision of the Podzolic soils in the British soil classification. Although classed with podzols because they have an iron-rich, or spodic horizon, they are, in fact intermediate between podzols and Brown earths. They are common on hilly land in western Europe, in climates where precipitation of more than about 900mm exceeds evapotranspiration for a large part of the year, and summers are relatively cool. The result is that leaching of the soil profile occurs; in which mobile chemicals are washed out of the topsoil, or A horizon, and accumulate lower down, in the B horizon.

Illuvium is material displaced across a soil profile, from one layer to another one, by the action of rainwater. The removal of material from a soil layer is called eluviation. The transport of the material may be either mechanical or chemical. The process of deposition of illuvium is termed illuviation. It is a water-assisted transport in a basically vertical direction, as compared to alluviation, the horizontal running water transfer. The resulting deposits are called illuvial deposits. Cutans are a type of illuvial deposit.

The Canadian System of Soil Classification is more closely related to the American system than any other, but they differ in several ways. The Canadian system is designed to cover only Canadian soils. The Canadian system dispenses with the sub-order hierarchical level. Solonetzic and Gleysolic soils are differentiated at the order level.

<span class="mw-page-title-main">Stagnosol</span> Saturated soil type

A Stagnosol in the World Reference Base for Soil Resources (WRB) is soil with strong mottling of the soil profile due to redox processes caused by stagnating surface water.

The Polish Soil Classification is a soil classification system used to describe, classify and organize the knowledge about soils in Poland.

A Retisol is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). Retisols are characterized by clay migration and an additional specific feature: The clay-poorer and lighter coloured eluvial horizon intercalates netlike into the clay-richer more intensely coloured illuvial horizon. The illuvial horizon is the diagnostic argic horizon, and the intercalation is called retic properties.

Moder is a forest floor type formed under mixed-wood and pure deciduous forests. Moder is a kind of humus whose properties are the transition between mor humus and mull humus types. Moders are similar to mors as they are made up of partially to fully humified organic components accumulated on the mineral soil. Compared to mulls, moders are zoologically active. In addition, moders present as in the middle of mors and mulls with a higher decomposition capacity than mull but lower than mor. Moders are characterized by a slow rate of litter decomposition by litter-dwelling organisms and fungi, leading to the accumulation of organic residues. Moder humus forms share the features of the mull and mor humus forms.

References

  1. ↑ Podzols by Otto Spaargaren in Encyclopedia of Soil Science, pp. 580-582
  2. ↑ Dimbleby, GW (1962). The Development of British Heathlands and Their Soils. Oxford Forestry Memoirs. Vol. 23. Oxford: Clarendon Press. OCLC   3814746.[ page needed ]
  3. ↑ Докучаев В. В. О подзоле Смоленской губернии // Труды Санкт-Петербургского общества естествоиспытателей. 1875. T. 6. Отд. минерал. и геол. Протоколы. С. XXI—XXII.
  4. ↑ Докучаев В. В. О подзоле // Труды Императорского Вольного экономического общества. 1880. T. 1. Вып. 2. С. 142—150.
  5. ↑ Rode A. A. To the problem of the degree of podzolization of soils // Studies in the genesis and geography of soils. M.: Acad. Sci. USSR, 1935. P. 55-70.
  6. ↑ Chesworth, W. (Eds.), 2008. Encyclopedia of soil science, The Netherlands.
  7. ↑ Spaargaren, Otto. Podzols. Encyclopedia of Soil Science, pp. 580–581.
  8. ↑ Gerding, Victor; Thiers, Oscar (2002), "Characterization of soils of Nothofagus betuloides (Mirb) Blume forests, in Tierra del Fuego, Chile", Revista chilena de historia natural (in Spanish), 75 (4): 819–833, doi: 10.4067/S0716-078X2002000400015
  9. 1 2 C., Park, Chris. A dictionary of environment and conservation. Allaby, Michael (3rd ed.). [Oxford]. ISBN   9780191826320. OCLC   970401188.{{cite book}}: CS1 maint: multiple names: authors list (link)
  10. 1 2 3 4 5 6 Scheffer, Fritz (2018). Lehrbuch der Bodenkunde. Schachtschabel, Paul; Blume, Hans-Peter (16. Aufl ed.). Heidelberg: Spektrum, Akad. Verl. ISBN   9783827414441. OCLC   506415938.
  11. 1 2 3 4 5 Lundström, U.S; Van Breemen, N.; Bain, D. (2000-02-01). "The podzolization process. A review". Geoderma. 94 (2–4): 91–107. Bibcode:2000Geode..94...91L. doi:10.1016/S0016-7061(99)00036-1. ISSN   0016-7061.
  12. 1 2 3 Sanborn, Paul; Lamontagne, Luc; Hendershot, William (2011-01-01). "Podzolic soils of Canada: Genesis, distribution, and classification". Canadian Journal of Soil Science. 91 (5): 843–880. doi:10.4141/cjss10024. ISSN   0008-4271.
  13. ↑ Buurman, P.; Jongmans, A.G. (2005-03-01). "Podzolisation and soil organic matter dynamics". Geoderma. 125 (1–2): 71–83. Bibcode:2005Geode.125...71B. doi:10.1016/j.geoderma.2004.07.006. ISSN   0016-7061.
  14. ↑ Fekiacova, Z.; Vermeire, M.L.; Bechon, L.; Cornelis, J.T.; Cornu, S. (2017-06-15). "Can Fe isotope fractionations trace the pedogenetic mechanisms involved in podzolization?". Geoderma. 296: 38–46. Bibcode:2017Geode.296...38F. doi:10.1016/j.geoderma.2017.02.020. ISSN   0016-7061.
  15. ↑ IUSS Working Group WRB (2022). "World Reference Base for Soil Resources, fourth edition" (PDF). International Union of Soil Sciences, Vienna. Retrieved 2023-08-18.
  16. ↑ "Keys to Soil Taxonomy 2014". Archived from the original on 2018-11-28. Retrieved 2018-11-27.
  17. ↑ Institute of Soil Science, Chinese Academy of Sciences (2001). Chinese Soil Taxonomy. Science Press, Beijing, New York.
  18. ↑ "Spodosols". geo.msu.edu. Archived from the original on 2018-03-30. Retrieved 2018-05-04.
  19. ↑ "Podzolic - Soils of Canada". www.soilsofcanada.ca. Archived from the original on 2018-04-22. Retrieved 2018-05-07.
  20. ↑ Canadian Agricultural Services Coordinating Committee. Soil Classification Working Group (1998). The Canadian system of soil classification (3rd ed.). Ottawa: NRC Research Press. ISBN   978-0585119052. OCLC   44961488.
  21. ↑ R.F. Isbell and the National Committee on Soil and Terrain (2016). "Australian Soil Classification, second edition (as Online Interactive Key)". CSIRO. Archived from the original on 29 February 2016. Retrieved 11 February 2016.
  22. ↑ dos Santos, Humberto Gonçalves; et al. (2018). Sistema Brasileira de Classificação de Solos, quinta edição. Embrapa, Brasilia.

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