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{{Short description|Typical soils of coniferous or boreal forests}}{{Infobox soil
|name=Podzol

|alternative_name=Podsol, Podosol, Spodosol, Espodossolo
|type=
|type_link=
|image=Podzol.jpg
|image_size=250px
|image_caption= 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 [[ironpan]]s.
|horizons='''H:''' common '''O:''' always, has [[humus|humified]] organic matter mixed with minerals '''A:''' absent in most boreal podzols<ref>Podzols by Otto Spaargaren in ''Encyclopedia of Soil Science'', pp. 580-582</ref> '''E:''' common, is ashen grey and leached in [[Iron|Fe]] and [[aluminium|Al]] '''B:''' always, receives Fe and Al through [[illuviation]] '''C:''' common
|composition_secondary=
|classification_system=[[World Reference Base for Soil Resources|WRB]], [[USDA soil taxonomy]], others
|parent_material=quartz rich debris and sediment
|profile=O(Ah)EBhsC
|code=PZ
|process=[[podzolization]]
|climate=[[humid continental climate|humid continental]], [[subarctic climate|subarctic]], [[oceanic climate|oceanic]], [[tropical rainforest climate|equatorial]]
}}

In [[soil science]], '''podzols''' are the typical [[soil]]s of [[conifer]]ous or [[Taiga|boreal forest]]s and also the typical soils of [[eucalypt]] forests and [[heath]]lands 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 [[moorland]]s with podzolic soils, [[cambisol]]s are preserved under [[Bronze Age]] barrows.<ref>{{cite book |last = Dimbleby |first = GW |year = 1962 |title = The Development of British Heathlands and Their Soils |series= Oxford Forestry Memoirs |volume = 23 |location = Oxford |publisher = Clarendon Press |oclc = 3814746 }}{{page needed|date=February 2023}}</ref>

== Term ==
Podzol means "under-ash" and is derived from the [[Russian language|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]].<ref>''Докучаев В. В.'' О подзоле Смоленской губернии // Труды Санкт-Петербургского общества естествоиспытателей. 1875. T. 6. Отд. минерал. и геол. Протоколы. С. XXI—XXII.</ref><ref>''Докучаев В. В.'' О подзоле // Труды Императорского Вольного экономического общества. 1880. T. 1. Вып. 2. С. 142—150.</ref> It refers to the common experience of [[Russia|Russian]] peasants of plowing up an apparent under-layer of ash (leached or [[Eluvium|E horizon]]) during first plowing of a virgin soil of that type.<ref>''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.</ref>

== 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.<ref>Chesworth, W. (Eds.), 2008. ''Encyclopedia of soil science'', The Netherlands.</ref> Most Podzols are poor soils for [[agriculture]] due to the sandy portion, resulting in a low level of moisture and [[nutrient]]s. 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 [[loam]]y types can be very productive for crops if [[agricultural lime|lime]] and [[fertilizer]] are used.

The E horizon (or Ae in Canadian soil classification system), which is usually {{convert|4|to|8|cm|in|1}} 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 {{convert|5|to|10|cm|in|1}} thick. In the middle, there is often a thin horizon of {{convert|0.5|to|1|cm|in|1}}. The bleached soil horizon, which always has a higher [[Munsell color system|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 {{convert|50|to|100|cm|in|-1}} progressively to the part of the soil that is mainly not affected by processes; that is the parent material. The [[soil profile]]s are designated by the letters A ([[topsoil]]), E ([[wikt:eluviation|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 '''[[Umbrisol]]s''' or '''[[inceptisols|Umbrepts]]'''.

==Geographic distribution==

[[File:Podzol map.svg|thumb|Distribution of Podzol soils according to the [[World Reference Base for Soil Resources]] classification:
{{legend|#d95f0e|Dominant (more than 50% of soil cover)}}
{{legend|#fec44f|Codominant (25-50%)}}
{{legend|#fff7bc|Associated (5-25%)}}]]

Podzols cover about {{convert|4850000|km2|mi2}} worldwide and are usually found under [[sclerophyll]]ous woody vegetation. By extent Podzols are most common in temperate and [[Taiga|boreal zones]] of the [[Northern Hemisphere]] but they can also be found in other settings including both [[temperate rainforest]]s and tropical areas.<ref name=EoSS>Spaargaren, Otto. Podzols. ''Encyclopedia of Soil Science'', pp. 580–581.</ref>

In South America Podzols occur beneath ''[[Nothofagus betuloides]]'' forests in [[Tierra del Fuego]].<ref name=GerdingThiers>{{Citation
| last1 = Gerding
| first1 = Victor
| last2 = Thiers
| first2 = Oscar
| title = Characterization of soils of Nothofagus betuloides (Mirb) Blume forests, in Tierra del Fuego, Chile
| journal = [[Revista chilena de historia natural]]
| volume = 75
| issue = 4
| year = 2002
| pages = 819–833
| language = es
| doi = 10.4067/S0716-078X2002000400015
| doi-access= free
}}</ref>

== Podzolization ==
[[File:Eisenhumuspodsol.jpg|thumb|upright|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<ref name=":0">{{Cite book|title=A dictionary of environment and conservation|last=C.|first=Park, Chris|others=Allaby, Michael|isbn=9780191826320|edition= 3rd|location=[Oxford]|oclc=970401188}}</ref>) is complex [[soil formation]] process by which dissolved [[Soil organic matter|organic matter]] and ions of [[iron]] and [[aluminium]], released through weathering of various minerals, form organo-mineral complexes ([[Chelation|chelates]]) and are moved from the upper parts of the soil profile and deposit in the deeper parts of soil. Through this process, the [[Eluvium|eluvial]] horizon becomes bleached and of ash-grey colour. The complexes move with percolating water further down to [[Illuviation|illuviated]] horizons which are commonly coloured brown, red or black as they accumulate and consist of cemented [[sesquioxide]]s and/or organic compounds. The podzolization is a typical soil formation process in Podzols.<ref name=":1">{{Cite book|title=Lehrbuch der Bodenkunde|last=Scheffer|first=Fritz|date=2018|publisher=Spektrum, Akad. Verl|others=Schachtschabel, Paul; Blume, Hans-Peter|isbn=9783827414441|edition= 16. Aufl|location=Heidelberg|oclc=506415938}}</ref><ref name=":0" />

=== 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.<ref name=":1" /><ref name=":2" /> Medium to coarse textured soils with base-poor [[parent material]] (usually rich in [[quartz]]) also promote podzolization, as they encourage percolating water flow.<ref name=":5">{{Cite journal|last=Sanborn|first=Paul|last2=Lamontagne|first2=Luc|last3=Hendershot|first3=William|date=2011-01-01|title=Podzolic soils of Canada: Genesis, distribution, and classification|journal=Canadian Journal of Soil Science|volume=91|issue=5|pages=843–880|doi=10.4141/cjss10024|issn=0008-4271}}</ref><ref name=":2">{{Cite journal|date=2000-02-01|title=The podzolization process. A review|journal=Geoderma|language=en|volume=94|issue=2–4|pages=91–107|doi=10.1016/S0016-7061(99)00036-1|issn=0016-7061|last1=Lundström|first1=U.S|last2=Van Breemen|first2=N.|last3=Bain|first3=D.|bibcode=2000Geode..94...91L}}</ref>

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

# Mobilization and translocation of organic matter, Fe and Al from the surface horizon, and
# Immobilization and stabilization of organic matter, Fe and Al into the subsoil.<ref>{{Cite journal|date=2005-03-01|title=Podzolisation and soil organic matter dynamics|journal=Geoderma|language=en|volume=125|issue=1–2|pages=71–83|doi=10.1016/j.geoderma.2004.07.006|issn=0016-7061|last1=Buurman|first1=P.|last2=Jongmans|first2=A.G.|bibcode=2005Geode.125...71B}}</ref><ref name=":2" /><ref>{{Cite journal|date=2017-06-15|title=Can Fe isotope fractionations trace the pedogenetic mechanisms involved in podzolization?|journal=Geoderma|language=en|volume=296|pages=38–46|doi=10.1016/j.geoderma.2017.02.020|issn=0016-7061|last1=Fekiacova|first1=Z.|last2=Vermeire|first2=M.L.|last3=Bechon|first3=L.|last4=Cornelis|first4=J.T.|last5=Cornu|first5=S.|url=http://orbi.ulg.ac.be/handle/2268/212632|bibcode=2017Geode.296...38F}}</ref>[[File:Podzol_A_soils.svg|thumb|Podzol A layers.]]

In the topsoil of acidic soils, organic matter (mostly from [[plant litter]], the humus layer and [[root exudate]]s) together with Al- and Fe-ions, form organo-mineral complexes. These soluble [[Chelation|chelates]] then relocate with percolating water from the [[A horizon|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<ref name=":5" />) can form, as the relocated Fe and Al and organic matter increase mineral particles, cementing them into this compacted layer.<ref name=":5" /><ref name=":1" /><ref name=":2" />

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 horizon]]s can result in the breakdown of metal-humus complexes. In the lower soil layers, the organic complexing agents can be degraded by functioning [[microorganism]]s. 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.<ref name=":1" /><ref name=":2" />

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.<ref name=":1" />

Podzolization also promotes the relocation of some nutrients ([[Copper|Cu]], [[Iron|Fe]], [[Manganese|Mn]], [[Molybdenum|Mo]] and [[Phosphorus|P]]) that sometimes brings them closer to plant [[root]]s.<ref name=":1" />

== 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]]''<ref>{{Cite web|url = https://wrb.isric.org/files/WRB_fourth_edition_2022-12-18.pdf|title = World Reference Base for Soil Resources, fourth edition|author = IUSS Working Group WRB|year = 2022|publisher = International Union of Soil Sciences, Vienna|access-date = 2023-08-18|url-status = live}}</ref> (WRB) and in many national soil classification systems (in some of them, spelled '''Podsols''').

* The ''[[USDA soil taxonomy]]''<ref name="ST">{{Cite web |url=https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/?cid=nrcs142p2_053580 |title=Keys to Soil Taxonomy 2014 |access-date=2018-11-27 |archive-date=2018-11-28 |archive-url=https://web.archive.org/web/20181128040416/https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/?cid=nrcs142p2_053580 |url-status=live }}</ref> and the ''Chinese soil taxonomy''<ref>{{Cite book|title = Chinese Soil Taxonomy|author=Institute of Soil Science, Chinese Academy of Sciences|year = 2001|publisher = Science Press, Beijing, New York}}</ref> call these soils '''Spodosols'''.<ref>{{Cite web|url=http://geo.msu.edu/extra/geogmich/spodosols.html|title=Spodosols|website=geo.msu.edu|access-date=2018-05-04|archive-date=2018-03-30|archive-url=https://web.archive.org/web/20180330055808/http://geo.msu.edu/extra/geogmich/spodosols.html|url-status=live}}</ref>
* The ''[[Canadian system of soil classification]]'' matches Podzols with soils under the '''Podzolic''' order (e.g. Humo-Ferric Podzol).<ref>{{Cite web|url=http://www.soilsofcanada.ca/orders/podzolic.php|title=Podzolic - Soils of Canada|website=www.soilsofcanada.ca|language=en|access-date=2018-05-07|archive-date=2018-04-22|archive-url=https://web.archive.org/web/20180422144018/http://www.soilsofcanada.ca/orders/podzolic.php|url-status=live}}</ref><ref>{{Cite book|title=The Canadian system of soil classification|author=Canadian Agricultural Services Coordinating Committee. Soil Classification Working Group|date=1998|publisher=NRC Research Press|isbn=978-0585119052|edition= 3rd|location=Ottawa|oclc=44961488}}</ref>
* The ''[[Australian Soil Classification]]''<ref>{{Cite web|url = http://www.clw.csiro.au/aclep/asc_re_on_line_V2/soilhome.htm|title = Australian Soil Classification, second edition (as Online Interactive Key)|author = R.F. Isbell and the National Committee on Soil and Terrain|year = 2016|access-date = 11 February 2016|publisher = CSIRO|archive-date = 29 February 2016|archive-url = https://web.archive.org/web/20160229004013/http://www.clw.csiro.au/aclep/asc_re_on_line_V2/soilhome.htm|url-status = live}}</ref> uses the term '''Podosols'''.
* The ''Brazilian Soil Classification System''<ref>{{Cite book|title = Sistema Brasileira de Classificação de Solos, quinta edição|author=dos Santos, Humberto Gonçalves|display-authors=etal|year = 2018|publisher = Embrapa, Brasilia}}</ref> calls them '''Espodossolos'''.

== See also ==
* [[Soil type]]

==References==
{{Reflist}}

==Further reading==
* W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the World. Springer, Berlin 2022, Chapter 3.3.3. {{ISBN|978-3-540-30460-9}}

== External links ==

* {{cite web| url =http://soils.usda.gov/technical/classification/orders/spodosols.html| title =Spodosols| publisher =USDA-NRCS| access-date =2006-05-14| url-status =dead| archive-url =https://web.archive.org/web/20060509223516/http://soils.usda.gov/technical/classification/orders/spodosols.html| archive-date =2006-05-09}}{{Dead link|date=July 2022}}
* {{cite web|url=http://grunwald.ifas.ufl.edu/Nat_resources/soil_orders/spodosols.htm |title=Spodosols |publisher=University of Florida |access-date=2006-05-14 |url-status=dead |archive-url=https://web.archive.org/web/20040918224312/http://grunwald.ifas.ufl.edu/Nat_resources/soil_orders/spodosols.htm |archive-date=September 18, 2004 }}
* {{cite web| url =http://soils.ag.uidaho.edu/soilorders/spodosols.htm| title =Spodosols| publisher =University of Idaho| access-date =2006-05-14| archive-url =https://web.archive.org/web/20060327074451/http://soils.ag.uidaho.edu/soilorders/spodosols.htm| archive-date =2006-03-27| url-status =dead}}
* [http://sis.agr.gc.ca/cansis/taxa/cssc3/chpt10.html The Podzolic Order]
* Podzol http://classification.soilweb.ca/podzol/
* http://edafologia.ugr.es/revista/tomo9b/a107text.pdf
* http://www.bauing.uni-wuppertal.de/boden/downloads_save/Podsol_Boden%20des%20Jahres_2007_JPNSS.pdf{{Dead link|date=May 2020 |bot=InternetArchiveBot |fix-attempted=yes }}
* [https://wrb.isric.org/picture-gallery/ profile photos (with classification)] WRB homepage
* [https://www.iuss.org/index.php?article_id=73|title=IUSS profile photos (with classification)] IUSS World of Soils

{{Soil type}}
{{Authority control}}

[[Category:Pedology]]
[[Category:Types of soil]]

Podzol - Revision history

Ajay Kumar: Created a new article