Editing Soil formation (section)

==History of research==
[[File:Soil-formation-factors-en.jpg|thumb|upright=1.5|Five factors of soil formation]]

===Dokuchaev's equation===
Russian geologist [[Vasily Dokuchaev]], commonly regarded as the father of pedology, determined in 1883<ref>{{citation |author=Dokuchaev, Vasily V. |title=Russian Chernozem |url=http://dlib.rsl.ru/viewer/01004897898#?page=249 }}</ref> that soil formation occurs over time under the influence of climate, vegetation, topography, and parent material. He demonstrated this in 1898 using the soil forming equation:<ref name=jenn80>{{citation |author-last=Jenny |author-first=Hans |author-link=Hans Jenny (pedologist)  |url=https://fr1lib.org/book/2137644/f3f28e |year=1980 |title=The soil resource: origin and behavior |series=Ecological Studies |volume=37 |publisher=[[Springer Science+Business Media|Springer-Verlag]] |location=New York, New York |isbn=978-1461261148 |quote=The idea that climate, vegetation, topography, parent material, and time control soils occurs in the writings of early naturalists. An explicit formulation was performed by Dokuchaev in 1898 in an obscure Russian journal unknown to western writers. He set down: soil = f(cl, o, p) t<sub>r</sub>  |access-date=6 March 2022 }}</ref>

: {{math| '''soil {{=}} ''f''(<var>cl</var>, <var>o</var>, <var>p</var>) t<sub>r</sub>'''}}
(where <var>cl</var> or <var>c</var> {{=}} climate, <var>o</var> {{=}} biological processes, <var>p</var> {{=}} parent material) <var>t<sub>r</sub></var> {{=}} relative time (young, mature, old)

===Hans Jenny's state equation===
American soil scientist [[Hans Jenny (pedologist)|Hans Jenny]] published in 1941<ref>{{cite book |last=Jenny |first=Hans |title=Factors of soil formation: a system of quantitative pedology |edition=First |date=1941 |publisher=[[McGraw-Hill Book Company, Inc.|McGraw-Hill]] |location=New York, New York |isbn=978-0486681283 |url=https://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download?cid=nrcseprd1330210&ext=pdf |access-date=6 March 2022 }}</ref> a state equation for the factors influencing soil formation:

: {{math| '''<var>S</var> {{=}} ''f''(<var>cl</var>, <var>o</var>, <var>r</var>, <var>p</var>, <var>t</var>, <var>...</var>)''' }}

* '''<var>S</var>''' soil formation
* '''<var>cl</var>''' (sometimes '''<var>c</var>''') climate
* '''<var>o</var>''' organisms (soil microbiology, soil mesofauna, soil biology)
* '''<var>r</var>''' relief
* '''<var>p</var>''' parent material
* '''<var>t</var>''' time

This is often remembered with the [[mnemonic]] Clorpt.

Jenny's state equation in Factors of Soil Formation differs from the Vasily Dokuchaev equation, treating time ('''t''') as a factor, adding topographic relief ('''r'''), and pointedly leaving the ellipsis "open" for more factors ([[state variables]]) to be added as our understanding becomes more refined.

There are two principal methods by which the state equation may be solved: first in a theoretical or conceptual manner by logical deductions from certain premises, and second empirically by experimentation or field observation. The empirical method is still mostly employed today, and soil formation can be defined by varying a single factor and keeping the other factors constant. This had led to the development of empirical models to describe pedogenesis, such as climofunctions, biofunctions, topofunctions, lithofunctions, and chronofunctions. Since Jenny published his formulation in 1941, it has been used by innumerable [[soil survey]]ors all over the world as a qualitative list for understanding the factors that may be important for producing the soil pattern within a region.<ref>{{cite journal |title=Reflections on the nature of soil and its biomantle |last1=Johnson |first1=Donald L. |last2=Domier |first2=Jane E. J. |last3=Johnson |first3=Diana N. |year=2005 |journal=[[Annals of the American Association of Geographers|Annals of the Association of American Geographers]] |volume=95 |pages=11–31 |doi=10.1111/j.1467-8306.2005.00448.x |s2cid = 73651791 |url=https://fr.art1lib.org/book/9534051/1972b7 |access-date=13 March 2022 }}</ref>

<!-- All covered above... ==Soil forming processes==
Soils develop from parent material by various weathering processes. [[Organic matter]] accumulation, [[decomposition]], and [[humus|humification]] are as critically important to soil formation as weathering. The zone of humification and weathering where pedogenic processes are dominant and where biota play an important role is termed the [[solum]].<ref>{{cite journal |last1=Juilleret |first1=Jérôme |last2=Dondeyne |first2=Stefaan |last3=Vancampenhout |first3=Karen |last4=Deckers |first4=Jozef |last5=Hissler |first5=Christophe |year=2016 |title=Mind the gap: a classification system for integrating the subsolum into soil surveys |journal=Geoderma |volume=264 |pages=332–39 |url=https://www.researchgate.net/publication/282271262 |access-date=13 March 2022 |doi=10.1016/j.geoderma.2015.08.031 |bibcode=2016Geode.264..332J }}</ref>

[[Soil acidification]] resulting from [[soil respiration]] supports chemical weathering. Plants contribute to chemical weathering through root exudates.<ref>{{cite journal |last1=Houben |first1=David |last2=Sonnet |first2=Philippe |year=2012 |title=Zinc mineral weathering as affected by plant roots |journal=[[Applied Geochemistry]] |volume=27 |issue=8 |pages=1587–92 |url=https://www.academia.edu/11364311 |access-date=13 March 2022 |doi=10.1016/j.apgeochem.2012.05.004 |bibcode=2012ApGC...27.1587H }}</ref> Soils can be enriched by deposition of [[sediment]]s on [[floodplain]]s and [[alluvial fan]]s, and by [[Aeolian processes#Deposition|wind-borne deposits]].<ref>{{cite journal |last1=Nihlén |first1=Tomas |last2=Mattson |first2=Jan O. |last3=Rapp |first3=Anders |last4=Gagaoudaki |first4=Chrisoula |last5=Kornaros |first5=Georges |last6=Papageorgiou |first6=John |year=1995 |title=Monitoring of Saharan dust fallout on Crete and its contribution to soil formation |journal=[[Tellus B: Chemical and Physical Meteorology]] |volume=47 |issue=3 |pages=365–74 |url=https://onlinelibrary.wiley.com/doi/pdf/10.1034/j.1600-0889.47.issue3.7.x |access-date=20 March 2022 |doi=10.3402/tellusb.v47i3.16055 |bibcode=1995TellB..47..365N |doi-access=free }}</ref>

Soil mixing (pedoturbation) is often an important factor in soil formation. Pedoturbation includes [[vertisol|churning clays]], [[cryoturbation]], and [[bioturbation]]. Types of bioturbation include faunal pedoturbation (animal [[burrow]]ing), plant pedoturbation (root growth, [[tree uprooting]]), and fungal pedoturbation ([[Mycelium|mycelial]] growth). Pedoturbation transforms soils through destratification, mixing, and [[stonelayer|sorting]], as well as creating preferential flow paths for [[soil gas]] and [[infiltration (hydrology)|infiltrating water]]. The zone of active bioturbation is termed the [[soil biomantle]].<ref>{{cite journal |last1=Johnson |first1=Donald L. |last2=Watson-Stegner |first2=Donna |last3=Johnson |first3=Diana N. |last4=Schaetzl |first4=Randall J. |year=1987 |title=Proisotropic and proanisotropic processes of pedoturbation |journal=Soil Science |volume=143 |issue=4 |pages=278–92 |url=https://fr.art1lib.org/book/58798898/077c76 |access-date=20 March 2022 |doi=10.1097/00010694-198704000-00005 |bibcode=1987SoilS.143..278J |s2cid=95532397 }}</ref>

Soil moisture content and water flow through the [[soil profile]] support [[Leaching (pedology)|leaching]] of [[solutes]], and [[eluviation]]. Eluviation is the translocation of [[colloid]] material, such as organic matter, clay and other mineral compounds. Transported constituents are deposited due to differences in soil moisture and soil chemistry, especially [[soil pH]] and [[redox potential]]. The interplay of removal (eluviation) and deposition ([[illuviation]]), also called ''pedotranslocation'', results in contrasting soil horizons.<ref>{{cite journal |last1=McKeague |first1=J. Alex |last2=St. Arnaud |first2=Roly J. |year=1969 |title=Pedotranslocation: eluviation-illuviation in soils during the Quaternary |journal=Soil Science |volume=107 |issue=6 |pages=428–34 |url=https://fr.art1lib.org/book/58287189/24ff2d |access-date=20 March 2022 |doi=10.1097/00010694-196906000-00007 |s2cid=93318719 }}</ref>

Key soil-forming processes especially important to macro-scale patterns of soil formation are:<ref name=Pidwirny2006>{{citation |last=Pidwirny |first= Michael |year=2006 |title=Soil pedogenesis |series=Fundamentals of Physical Geography |edition=second |url=http://www.physicalgeography.net/fundamentals/10u.html |access-date=20 March 2022 }}</ref>
* [[Laterite|Laterization]]
* [[Podsolization]]
* [[Calcification]]
* [[Soil salinity|Salinization]]
* [[Gleysol|Gleization]]-->