Oxisol: Difference between revisions

{{short description|A soilSoil type known for occurring in tropical rain forests}}

'''Oxisols''' are ana [[soil]] order in [[USDA soil taxonomy]], best known for their occurrence in [[tropical]] [[rain forest]], 15–25within 25 degrees north and south of the [[Equator]]. In the [[World Reference Base for Soil Resources]] (WRB),<ref>{{Cite web|url = httphttps://wwwwrb.faoisric.org/3files/i3794en/I3794enWRB_fourth_edition_2022-12-18.pdf|title = World Reference Base for Soil Resources 2014, Updatefourth 2015edition|author=IUSS Working Group WRB|year = 20152022|publisher = WorldInternational SoilUnion Resourcesof ReportsSoil 106Sciences, FAO, RomeVienna}}</ref> (WRB), they belong mainly to the [[Ferralsolferralsol]]s, but some are [[Plinthosolplinthosol]]s or [[Nitisolnitisol]]s. Some Oxisolsoxisols have been previously classified as [[laterite]] soils.

The main processes of [[soil formation]] of Oxisolsoxisols are [[weathering]], [[humification]] and [[pedoturbation]] due to animals. These processes produce the characteristic [[soil profile]]. They are defined as soils containing ''at all depths'' no more than 10ten percent weatherable [[minerals]], and low [[cation exchange capacity]]. Oxisols are always a red or yellowish color, due to the high concentration of [[iron]](III) and [[aluminium]] [[oxides]] and [[hydroxide]]s. They also contain [[quartz]] and [[kaolin]], plus small amounts of other [[clay minerals]] and [[organic matter]].

The word "Oxisoloxisol" comes from ''"oxide"'' in reference to the dominance of oxide minerals such as [[bauxite]]. In the [[World Reference Base for Soil Resources]], Oxisolsoxisols are known as ''Ferralsolsferralsols''.

Present-day Oxisolsoxisols are found almost exclusively in tropical areas, in [[South America]] and [[Africa]], almost always on highly stable continental [[craton]]s.

In [[Southeast Asia#GeographicalGeography|Southeast Asia]], Oxisolsoxisols are found on remnants of the [[Cimmeria (continent)|Cimmerian microcontinent]], and on the [[Shan–Thai Terrane]]. In [[Geography of Thailand|Thailand]], Rhodicrhodic Ferralsolsferralsols, called [[Yasothon Province|Yasothon]] soils, are said to have formed under humid tropical conditions in the early [[Tertiary]], on an extensive plain later uplifted to form the [[Khorat Plateau]]. Characterized by a bright red color, these [[relict (geology)|relict]] soils occur on uplands in a great semicircle around the southern rim, overlying associated [[gravel]] [[Soil horizon|horizon]]s said to have been cleared of [[sand]] by [[termites]], in a prolonged and still on-going process of [[bioturbation]]. Xanthic Ferralsolsferralsols of the [[Nakhon Ratchasima Province|Khorat]] and [[Ubon Ratchathani Province|Udon]] Seriesseries, characterized by a pale yellow to brown color, developed in midlands in processes still under investigation; as are those forming lowland soils resembling European [[brown soil]]s.<ref>Lofjle, E.; Kubiniok, J. ''Landform development and bioturbation on the Khorat plateau, Northeast Thailand'', Nat.Hist.Bull.Siam Soc. (56), 1996 {{cite web |url=http://www.aseanbiodiversity.info/Abstract/53002297.pdf |title=Archived copy |accessdateaccess-date=2010-12-23 |url-status=dead |archiveurlarchive-url=https://web.archive.org/web/20110721184927/http://www.aseanbiodiversity.info/Abstract/53002297.pdf |archivedatearchive-date=2011-07-21 }}</ref>

In [[Australia]] vast areas formerly covered in rainforest have become so dry that Oxisolsoxisols have formed a hard [[ironstone]] cover upon which only [[Orthents|skeletal soils]] can form.

[[Fossil]] Oxisolsoxisols are known from the first appearance of free [[oxygen]] in the [[Earth's atmosphere|atmosphere]] about 2,200 million years ago. In warm periods like the [[Mesozoic]] and [[Paleocene]], Oxisolsoxisols extended to areas that now have quite cool climates, extending well into [[North America]] and [[Europe]]. It is believed Oxisolsoxisols became vegetated later than [[Ultisolsultisols]] or [[Alfisolsalfisols]], probably because vegetation took a long time to adapt to the infertility of Oxisolsoxisols.

Oxisols are often used for tropical crops such as [[Cocoa bean|cocoa]] and [[rubber]]. In some cases, [[rice]] is grown on them. Permanent cropping of Oxisolsoxisols in low-income areas is very difficult because of low [[cation exchange]] capacities and high [[phosphorus]] fixation on iron and aluminium oxides (ligand exchange mechanism; [[inner sphere complex]] with phosphate). However, many Oxisolsoxisols can be cultivated over a wide range of moisture conditions. On this account, Oxisolsoxisols are intensively exploited for agriculture in some regions which have enough wealth to support modern agricultural practices (including regular additions of [[lime (mineral)|lime]] and [[fertilizer]]). A recent example of exploitation by modern methods involves the growing of [[soybeans]] in [[Brazil]].

* '''Aquox''' – Oxisolsoxisols with a water table at or near the surface for much of the year

* '''Perox''' – Oxisolsoxisols of continuously humid climates, where precipitation exceeds evapotranspiration in all months

* '''Torrox''' – Oxisolsoxisols of arid climates. Because the present climate can never produce enough weathering to produce oxisols, torrox soils are always [[paleosols]] formed during periods of much wetter climates. They occur mainly in [[Southern Africa]].

* '''Ustox''' – Oxisolsoxisols of semiarid and subhumid climates

* '''Udox''' – Oxisolsoxisols of humid climates

== NotesReferences ==

* {{cite web| url =http://soilsgrunwald.ifas.usdaufl.govedu/technicalNat_resources/classification/orderssoil_orders/oxisols.htmlhtm | title =Oxisols | publisher =USDA-NRCS|University accessdateof Florida |access-date=2006-05-14| |url-status =dead| archiveurl |archive-url=https://web.archive.org/web/2006020622402620060916044316/http://soilsgrunwald.usdaifas.govufl.edu/technicalNat_resources/classification/orderssoil_orders/oxisols.htmlhtm |archive-date=September archivedate16, =2006-02-06 }}

* {{cite web| url =http://grunwaldsoils.ifasag.ufluidaho.edu/Nat_resources/soil_orderssoilorders/oxisols.htm | title =Oxisols | publisher =University of Florida Idaho|accessdate access-date =2006-05-14 |url archive-status=deadurl |archiveurl=https://web.archive.org/web/2006091604431620060604031120/http://grunwaldsoils.ifasag.ufluidaho.edu/Nat_resources/soil_orderssoilorders/oxisols.htm |archivedate=September 16,archive-date =2006-06-04| url-status =dead}}

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