Editing Soil formation

{{Short description|Process of soil formation}}
{{redirect|Pedogenesis|the reproduction by an organism that has not achieved physical maturity|Paedogenesis}}
{{Use dmy dates|date=October 2019}}
[[File:Great Soil Structure in Stehly Crop Field in Eastern, SD (21480483232).jpg|thumb|Soil created on a [[No-till farming|no-till farm]] in [[South Dakota]], [[United States]]]]
'''Soil formation''', also known as '''pedogenesis''', is the process of [[soil]] genesis as regulated by the effects of place, environment, and history. [[Biogeochemistry|Biogeochemical]] processes act to both create and destroy order ([[anisotropy]]) within soils. These alterations lead to the development of layers, termed [[soil horizons]], distinguished by differences in [[soil color|color]], [[soil structure|structure]], [[soil texture|texture]], and [[Soil#Chemistry|chemistry]]. These [[soil morphology|features]] occur in patterns of [[soil type]] distribution, forming in response to differences in soil forming factors.<ref>{{cite book |last1=Buol |first1=Stanley W. |last2=Southard |first2=Randal J. |last3=Graham |first3=Robert C. |last4=McDaniel |first4=Paul A. |title=Soil genesis and classification |edition=Sixth |date=2011 |publisher=[[Wiley-Blackwell]] |location=Hoboken, New Jersey |isbn=978-0-813-80769-0 |url=https://book4you.org/book/2156097/707d35 |access-date=26 September 2021 }}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Pedogenesis is studied as a branch of [[pedology]], the study of soil in its natural environment. Other branches of pedology are the study of [[soil morphology]] and [[soil classification]]. The study of pedogenesis is important to understanding soil distribution patterns in current ([[soil survey|soil geography]]) and past ([[paleopedology]]) geologic periods.

==Overview==
Soil develops through a series of changes.<ref>{{cite book |last1=Jenny |first1=Hans |title=Factors of soil formation: a system of quantitative pedology |year=1994 |publisher=Dover |location=New York, New York |isbn=978-0-486-68128-3 |url=https://book4you.org/book/832215/90064b |access-date=26 September 2021 |archive-url=https://web.archive.org/web/20130225050838/http://soilandhealth.org/01aglibrary/010159.Jenny.pdf |archive-date=25 February 2013 |url-status=live }}</ref> The starting point is [[weathering]] of freshly accumulated [[parent material]]. A variety of soil microbes ([[bacteria]], [[archaea]], [[Fungus|fungi]]) feed on simple compounds ([[nutrients]]) released by weathering and produce organic acids and specialized proteins which contribute in turn to mineral weathering. They also leave behind [[biotic material|organic residues]] which contribute to [[humus]] formation.<ref>{{cite book |last1=Samuels |first1=Toby |last2=Bryce |first2=Casey |last3=Landenmark |first3=Hanna |last4=Marie-Loudon |first4=Claire |last5=Nicholson |first5=Natasha |last6=Stevens |first6=Adam H. |last7=Cockell |first7=Charles |year=2020 |chapter=Microbial weathering of minerals and rocks in natural environments |title=Biogeochemical cycles: ecological drivers and environmental impact |pages=59–79 |editor-last1=Dontsova |editor-first1=Katerina |editor-last2=Balogh-Brunstad |editor-first2=Zsuzsanna |editor-last3=Le Roux |editor-first3=Gaël |publisher=[[Wiley-Blackwell]] |location=Hoboken, New Jersey |isbn=978-1-119-41331-8 |chapter-url=https://www.researchgate.net/publication/334319081 |doi=10.1002/9781119413332.ch3 |s2cid=216360850 |access-date=26 September 2021}}</ref> Plant roots with their symbiotic [[mycorrhiza]]l fungi are also able to extract nutrients from [[Rock (geology)|rocks]].<ref>{{cite journal |last1=Augusto |first1=Laurent |last2=Fanin |first2=Nicolas |last3=Bakker |first3=Mark R. |journal=[[Functional Ecology (journal)|Functional Ecology]] |volume=33 |issue=5 |title=When plants eat rocks: functional adaptation of roots on rock outcrops |year=2019 |url=https://www.researchgate.net/publication/332964580 |pages=760‒61 |doi=10.1111/1365-2435.13325 |s2cid=164450031 |access-date=26 September 2021 |doi-access=free |bibcode=2019FuEco..33..760A }}</ref>

New soils increase in depth by a combination of weathering and further [[deposition (geology)|deposition]]. The [[soil production function|soil production]] rate due to weathering is approximately 1/10&nbsp;mm per year.<ref>{{cite journal |title=The role of pedogenic overprinting in the obliteration of parent material in some polygenetic landscapes of Sicily (Italy) |last1=Scalenghe |first1=Riccardo |last2=Territo |first2=Claudio |last3=Petit |first3=Sabine |last4=Terribile |first4=Fabio |last5=Righi |first5=Dominique |year=2016 |doi=10.1016/j.geodrs.2016.01.003 |journal=Geoderma Regional |volume=7 |issue=1 |pages=49–58 |bibcode=2016GeodR...7...49S |url=https://art1lib.org/book/54626974/c3872a |access-date=26 September 2021 |archive-date=26 September 2021 |archive-url=https://web.archive.org/web/20210926082245/https://art1lib.org/book/54626974/c3872a |url-status=dead }}</ref> New soils can also deepen from [[aeolian processes|dust deposition]]. Gradually soil is able to support higher forms of plants and animals, starting with [[pioneer species]] and proceeding along [[ecological succession]] to more complex [[soil food web|plant and animal communities]].<ref>{{cite book |last=Mirsky |first=Arthur |title=Soil development and ecological succession in a deglaciated area of Muir Inlet, Southeast Alaska |year=1966 |publisher=[[Ohio State University]] Research Foundation |location=Columbus, Ohio |url=https://kb.osu.edu/bitstream/handle/1811/38513/IPS_Report_20_%20p_i-xxi_1-18.pdf |access-date=3 October 2021 }}</ref> [[Topsoil]]s deepen with the accumulation of humus originating from dead remains of [[vascular plants|higher plants]] and soil microbes.<ref>{{cite journal |title=Soil development on the Crimean Peninsula in the Late Holocene |last1=Lisetskii |first1=Fedor N. |last2=Ergina |first2=Elena I. |year=2010 |doi=10.1134/S1064229310060013 |journal=Eurasian Soil Science |volume=43 |issue=6 |pages=601–13 |bibcode=2010EurSS..43..601L |s2cid=128834822 |url=https://www.researchgate.net/publication/227297100 |access-date=3 October 2021 }}</ref> They also deepen through [[Perturbation (geology)|mixing]] of organic matter with weathered minerals.<ref>{{cite journal |title=Exploring pedogenesis via nuclide-based soil production rates and OSL-based bioturbation rates |last1=Wilkinson |first1=Marshall T. |last2=Humphreys |first2=Geoff S. |year=2005 |doi=10.1071/SR04158 |journal=Australian Journal of Soil Research |volume=43 |issue=6 |pages=767–79 |bibcode=2005SoilR..43..767W |url=https://art1lib.org/book/63951907/03ecca |access-date=3 October 2021 |archive-date=3 October 2021 |archive-url=https://web.archive.org/web/20211003083423/https://art1lib.org/book/63951907/03ecca |url-status=dead }}</ref> As soils mature, they develop [[soil horizon]]s as organic matter accumulates and mineral weathering and leaching take place.

==Factors==

Soil formation is influenced by at least five classic factors that are intertwined in the evolution of a soil. They are: parent material, climate, topography (relief), organisms, and time.<ref name="Jenny1941">{{cite book |last=Jenny |first=Hans |title=Factors of soil formation: a system of qunatitative pedology |year=1941 |publisher=[[McGraw-Hill]] |location=New York |url=http://netedu.xauat.edu.cn/sykc/hjx/content/ckzl/6/2.pdf |access-date=10 October 2021 |archive-url=https://web.archive.org/web/20170808104008/http://netedu.xauat.edu.cn/sykc/hjx/content/ckzl/6/2.pdf |archive-date=8 August 2017 |url-status=live }}</ref> When reordered to climate, organisms, relief, parent material, and time, they form the acronym CLORPT.<ref>{{cite journal |last1=Johnson |first1=Donald Lee |last2=Domier |first2=Jane E. J. |last3=Johnson |first3=Diana N. |year=2005 |title=Reflections on the nature of soil and its biomantle |journal=[[Annals of the American Association of Geographers|Annals of the Association of American Geographers]] |volume=95 |issue=1 |pages=11–31 |url=https://art1lib.org/book/9534051/1972b7 |doi=10.1111/j.1467-8306.2005.00448.x |s2cid=73651791 |access-date=24 May 2022 |archive-date=20 October 2022 |archive-url=https://web.archive.org/web/20221020125200/https://art1lib.org/book/9534051/1972b7 |url-status=dead }}</ref>

===Parent material===
The mineral material from which a soil forms is called [[parent material]]. Rock, whether its origin is [[Igneous rock|igneous]], [[Sedimentary rock|sedimentary]], or [[Metamorphic rock|metamorphic]], is the source of all soil mineral materials and the origin of all [[Plant nutrients in soil|plant nutrients]] with the exceptions of [[nitrogen]], [[hydrogen]] and [[carbon]]. As the [[parent rock]] is chemically and physically [[Weathering|weathered]], [[Sediment transport|transported]], [[Deposition (geology)|deposited]] and [[Precipitation (chemistry)|precipitated]], it is transformed into a soil.<ref>{{cite book |last1=Weil |first1=Ray R. |last2=Brady |first2=Nyle C. |title=The nature and properties of soils |edition=Fifteenth |date=2016 |publisher=[[Pearson Education|Pearson]] |location=London, United Kingdom |isbn=978-1292162232 |url=https://book4you.org/book/3515307/ce41a0 |access-date=10 October 2021 }}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Typical soil parent mineral materials are:{{sfn|Donahue|Miller|Shickluna|1977|pp=20–21}}
* [[Quartz]]: SiO<sub>2</sub>
* [[Calcite]]: CaCO<sub>3</sub>
* [[Feldspar]]: KAlSi<sub>3</sub>O<sub>8</sub>
* [[Mica]] (biotite): {{chem|K(Mg,Fe)|3|(AlSi|3|O|10|)(F,OH)|2}}

[[File:Lössacker.jpg|thumb|Soil, on an agricultural field in Germany, which has formed on [[loess]] parent material]]
Parent materials are classified according to how they came to be deposited. Residual materials are mineral materials that have weathered in place from primary [[bedrock]]. Transported materials are those that have been deposited by water, wind, ice or gravity. Cumulose material is organic matter that has grown and accumulates in place.<ref>{{cite web |url=https://landscape.soilweb.ca/organic-environment/ |title=Organic environment |website=[[University of British Columbia]] and [[Agriculture and Agri-Food Canada]] |access-date=17 October 2021 }}</ref>

Residual soils are soils that develop from their underlying parent rocks and have the same general chemistry as those rocks.<ref>{{cite journal |last1=Rahardjo |first1=Harianto |last2=Aung |first2=K. K. |last3=Leong |first3=Eng Choon |last4=Rezaur |first4=R. Bhuiyan |year=2004 |title=Characteristics of residual soils in Singapore as formed by weathering |journal=[[Engineering Geology (journal)|Engineering Geology]] |volume=73 |issue=1 |pages=157–69 |url=https://www.academia.edu/25563851 |doi=10.1016/j.enggeo.2004.01.002 |bibcode=2004EngGe..73..157R |access-date=17 October 2021 }}</ref> The soils found on [[mesa]]s, [[plateau]]x, and [[plain]]s are residual soils. In the United States as little as three percent of the soils are residual.{{sfn|Donahue|Miller|Shickluna|1977|p=21}}

Most soils derive from transported materials that have been moved many miles by wind, water, ice and gravity:
* [[Aeolian processes]] (movement by wind) are capable of moving [[silt]] and fine [[sand]] many hundreds of miles, forming [[loess]] soils (60–90 percent silt),{{sfn|Donahue|Miller|Shickluna|1977|p=24}} common in the [[Midwestern United States]] and Canada, north-western Europe, Argentina and [[Central Asia]]. Clay is seldom moved by wind as it forms stable aggregates.<ref>{{cite journal |last1=Shahabinejad |first1=Nader |last2=Mahmoodabadi |first2=Majid |last3=Jalalian |first3=Ahmad |last4=Chavoshi |first4=Elham |year=2019 |title=The fractionation of soil aggregates associated with primary particles influencing wind erosion rates in arid to semiarid environments |journal=Geoderma |volume=356 |issue=113936 |page=113936 |url=https://coek.info/pdf-the-fractionation-of-soil-aggregates-associated-with-primary-particles-influenci.html |doi=10.1016/j.geoderma.2019.113936 |bibcode=2019Geode.35613936S |s2cid=202908885 |access-date=17 October 2021 }}</ref>
* Water-transported materials are classed as either [[Alluvium|alluvial]], [[Lake|lacustrine]], or marine. Alluvial materials are those moved and deposited by flowing water. [[Sediment|Sedimentary deposits]] settled in lakes are called lacustrine. [[Lake Bonneville]] and many soils around the [[Great Lakes]] are examples. Marine deposits, such as soils along the Atlantic and [[Gulf Coast of the United States|Gulf Coast]]s and in the [[Imperial Valley]] of California are the beds of ancient seas that have been revealed as the land uplifted.<ref>{{cite journal |last1=Merritts |first1=Dorothy J. |last2=Chadwick |first2=Oliver A. |last3=Hendricks |first3=David M. |year=1991 |title=Rates and processes of soil evolution on uplifted marine terraces, northern California |journal=Geoderma |volume=51 |issue=1–4 |pages=241–75 |url=https://coek.info/pdf-rates-and-processes-of-soil-evolution-on-uplifted-marine-terraces-northern-calif.html |doi=10.1016/0016-7061(91)90073-3 |bibcode=1991Geode..51..241M |access-date=24 October 2021 }}</ref>
* Ice moves parent material and makes deposits in the form of terminal and lateral [[moraine]]s in the case of stationary glaciers. Retreating glaciers leave smoother ground moraines, and in all cases [[outwash plain]]s are left as alluvial deposits are moved downstream from the glacier.<ref>{{cite journal |last1=Luehmann |first1=Michael D. |last2=Peter |first2=Brad G. |last3=Connallon |first3=y Christopher B. |last4=Schaetz |first4=Randall J. |last5=Smidt |first5=Samuel J. |last6=Liu |first6=Wei |last7=Kincare |first7=Kevin A. |last8=Walkowiak |first8=Toni A. |last9=Thorlund |first9=Elin |last10=Holler |first10=Marie S. |year=2016 |title=Loamy, two-storied soils on the outwash plains of southwestern lower Michigan: pedoturbation of loess with the underlying sand |journal=[[Annals of the American Association of Geographers]] |volume=106 |issue=3 |pages=551–72 |url=https://people.geo.msu.edu/schaetzl/PDFs/Luehmann%20et%20al.%202016.pdf |doi=10.1080/00045608.2015.1115388 |bibcode=2016AAAG..106..551L |s2cid=131571035 |access-date=24 October 2021 }}</ref>
* Parent material moved by gravity is obvious at the base of steep slopes as [[Scree|talus cones]] and is called [[Colluvium|colluvial]] material.<ref>{{cite journal |last1=Zádorová |first1=Tereza |last2=Penížek |first2=Vit |year=2018 |title=Formation, morphology and classification of colluvial soils: a review |journal=European Journal of Soil Science |volume=69 |issue=4 |pages=577–91 |url=https://booksc.eu/book/70643184/1cb921 |doi=10.1111/ejss.12673 |bibcode=2018EuJSS..69..577Z |s2cid=102565037 |access-date=31 October 2021 }}</ref>

Cumulose parent material is not moved but originates from deposited organic material. This includes [[peat]] and [[Muck (soil)|muck soils]] and results from preservation of plant residues by the low oxygen content of a high [[water table]]. While peat may form sterile soils, muck soils may be very fertile.<ref>{{cite book |last1=Shutt |first1=Frank T. |last2=Wright |first2=L. E. |title=Peat muck and mud deposits: their nature, composition and agricultural uses |year=1933 |publisher=Dominion of Canada, Department of Agriculture |location=Ottawa, Ontario, Canada |url=https://atrium.lib.uoguelph.ca/xmlui/bitstream/handle/10214/15157/FDMR_peat_muck_mud_deposits_1933.pdf |access-date=31 October 2021 }}</ref>

==== Weathering ====
The weathering of parent material takes the form of physical weathering (disintegration), chemical weathering (decomposition) and chemical transformation. Weathering is usually confined to the top few meters of geologic material, because physical, chemical, and biological stresses and fluctuations generally decrease with depth.<ref>{{cite web |url=http://uregina.ca/~sauchyn/geog323/weather.html |title=Weathering |website=University of Regina |access-date=7 November 2021 }}</ref> Physical disintegration begins as rocks that have solidified deep in the Earth are exposed to lower pressure near the surface and swell and become mechanically unstable. Chemical decomposition is a function of mineral solubility, the rate of which doubles with each 10&nbsp;°C rise in temperature but is strongly dependent on water to effect chemical changes. Rocks that will decompose in a few years in tropical climates will remain unaltered for millennia in deserts.<ref name="Gilluly1975">{{cite book |author-link1=James Gilluly |last1=Gilluly |first1=James |last2=Waters |first2=Aaron Clement |last3=Woodford |first3=Alfred Oswald |title=Principles of geology |date=1975 |edition=4th |publisher=W.H. Freeman |location=San Francisco, California |isbn=978-0-7167-0269-6 }}</ref> Structural changes are the result of [[Hydration reaction|hydration]], [[Redox|oxidation]], and [[Redox|reduction]]. Chemical weathering mainly results from the excretion of [[organic acids]] and [[chelating]] compounds by bacteria<ref>{{cite journal |last1=Uroz |first1=Stéphane |last2=Calvaruso |first2=Christophe |last3=Turpault |first3=Marie-Pierre |last4=Frey-Klett |first4=Pascale |year=2009 |title=Mineral weathering by bacteria: ecology, actors and mechanisms |journal=[[Trends in Microbiology]] |volume=17 |issue=8 |pages=378–87 |doi=10.1016/j.tim.2009.05.004 |pmid=19660952 |url=https://art1lib.org/book/17303331/fda878 |access-date=7 November 2021 |archive-date=7 November 2021 |archive-url=https://web.archive.org/web/20211107091125/https://art1lib.org/book/17303331/fda878 |url-status=dead }}</ref> and fungi,<ref name="Landeweert2001">{{cite journal |last1=Landeweert |first1=Renske |last2=Hoffland |first2=Ellis |last3=Finlay |first3=Roger D. |last4=Kuyper |first4=Thom W. |last5=Van Breemen |first5=Nico |year=2001 |title=Linking plants to rocks: ectomycorrhizal fungi mobilize nutrients from minerals |journal=[[Trends in Ecology and Evolution]] |volume=16 |issue=5 |pages=248–54 |doi=10.1016/S0169-5347(01)02122-X |pmid=11301154 |url=https://www.academia.edu/13679137 |access-date=7 November 2021 }}</ref> thought to increase under [[greenhouse effect]].<ref>{{cite journal |last1=Andrews |first1=Jeffrey A. |last2=Schlesinger |first2=William H. |year=2001 |title=Soil CO2 dynamics, acidification, and chemical weathering in a temperate forest with experimental CO2 enrichment |journal=Global Biogeochemical Cycles |volume=15 |issue=1 |pages=149–62 |doi=10.1029/2000GB001278 |bibcode=2001GBioC..15..149A |s2cid=128612522 |url=https://www.researchgate.net/publication/248816941 |access-date=7 November 2021 |doi-access=free }}</ref>
* ''Physical disintegration'' is the first stage in the transformation of parent material into soil. Temperature fluctuations cause expansion and contraction of the rock, splitting it along lines of weakness.<ref>{{cite journal |last1=Halsey |first1=Dave P. |last2=Mitchell |first2=David J. |last3=Dews |first3=S. J. |year=1998 |title=Influence of climatically induced cycles in physical weathering |journal=[[Quarterly Journal of Engineering Geology & Hydrogeology|Quarterly Journal of Engineering Geology and Hydrogeology]] |volume=31 |issue=4 |pages=359–67 |url=https://art1lib.org/book/35607238/7259bb |doi=10.1144/GSL.QJEG.1998.031.P4.09 |bibcode=1998QJEGH..31..359H |s2cid=128917530 |access-date=7 November 2021 }}</ref> Water may then enter the cracks and freeze and cause the physical splitting of material along a path toward the center of the rock, while temperature gradients within the rock can cause exfoliation of "shells". Cycles of wetting and drying cause soil particles to be abraded to a finer size, as does the physical rubbing of material as it is moved by wind, water, and gravity. Organisms may reduce parent material size and create crevices and pores through the mechanical action of plant roots and the digging activity of animals.{{sfn|Donahue|Miller|Shickluna|1977|pp=28–31}} 
* ''Chemical decomposition'' and ''structural changes'' result when minerals are made soluble by water or are changed in structure. The first three of the following list are solubility changes, and the last three are structural changes.{{sfn|Donahue|Miller|Shickluna|1977|pp=31–33}}

# The ''[[Solution (chemistry)|solution]]'' of salts in water results from the action of bipolar [[water molecules]] on [[ionic salt]] compounds producing a solution of ions and water, removing those minerals and reducing the rock's integrity, at a rate depending on [[water flow]] and pore channels.<ref>{{cite journal |last1=Li |first1=Li |last2=Steefel |first2=Carl I. |last3=Yang |first3=Li |year=2008 |title=Scale dependence of mineral dissolution rates within single pores and fractures |journal=[[Geochimica et Cosmochimica Acta]] |volume=72 |issue=2 |pages=360–77 |url=https://www.researchgate.net/publication/223835697 |doi=10.1016/j.gca.2007.10.027 |access-date=14 November 2021 |bibcode=2008GeCoA..72..360L |archive-date=1 November 2015 |archive-url=https://web.archive.org/web/20151101231923/http://lili.ems.psu.edu/publication/liligca08.pdf |url-status=live }}</ref>
# ''[[Hydrolysis]]'' is the transformation of minerals into [[Chemical polarity|polar]] molecules by the splitting of intervening water. This results in soluble [[acid-base]] pairs. For example, the hydrolysis of [[orthoclase]]-[[feldspar]] transforms it to acid [[silicate]] clay and basic [[potassium hydroxide]], both of which are more soluble.<ref>{{cite journal |last1=Oelkers |first1=Eric H. |last2=Schott |first2=Jacques |year=1995 |title=Experimental study of anorthite dissolution and the relative mechanism of feldspar hydrolysis |journal=[[Geochimica et Cosmochimica Acta]] |volume=59 |issue=24 |pages=5039–53 |url=https://art1lib.org/book/19648369/edea24 |doi=10.1016/0016-7037(95)00326-6 |bibcode=1995GeCoA..59.5039O |access-date=14 November 2021 }}</ref>
# In ''[[carbonation]]'', the solution of [[carbon dioxide]] in water forms [[carbonic acid]]. Carbonic acid will transform [[calcite]] into more soluble [[calcium bicarbonate]].<ref>{{cite journal |last1=Al-Hosney |first1=Hashim |last2=Grassian |first2=Vicki H. |year=2004 |title=Carbonic acid: an important intermediate in the surface chemistry of calcium carbonate |journal=[[Journal of the American Chemical Society]] |volume=126 |issue=26 |pages=8068–69 |doi=10.1021/ja0490774 |pmid=15225019 |bibcode=2004JAChS.126.8068A |url=https://art1lib.org/book/18790192/b47eec |access-date=14 November 2021 }}</ref>
# ''[[Hydration reaction|Hydration]]'' is the inclusion of water in a mineral structure, causing it to swell and leaving it stressed and easily [[Chemical decomposition|decomposed]].<ref>{{cite journal |last1=Jiménez-González |first1=Inmaculada |last2=Rodríguez-Navarro |first2=Carlos |last3=Scherer |first3=George W. |year=2008 |title=Role of clay minerals in the physicomechanical deterioration of sandstone |journal=[[Journal of Geophysical Research]] |volume=113 |issue=F02021 |pages=1–17 |doi=10.1029/2007JF000845 |bibcode=2008JGRF..113.2021J |doi-access=free }}</ref>
# ''[[Oxidation]]'' of a mineral compound is the inclusion of [[oxygen]] in a mineral, causing it to increase its [[oxidation number]] and swell due to the relatively large size of oxygen, leaving it stressed and more easily attacked by water (hydrolysis) or carbonic acid (carbonation).<ref>{{cite journal |last1=Mylvaganam |first1=Kausala |last2=Zhang |first2=Liangchi |year=2002 |title=Effect of oxygen penetration in silicon due to nano-indentation |journal=[[Nanotechnology (journal)|Nanotechnology]] |volume=13 |issue=5 |pages=623–26 |url=https://www.researchgate.net/publication/230680185 |doi=10.1088/0957-4484/13/5/316 |access-date=14 November 2021 |bibcode=2002Nanot..13..623M |s2cid=250738729 }}</ref>
# ''[[Redox|Reduction]]'', the opposite of oxidation, means the removal of oxygen, hence the oxidation number of some part of the mineral is reduced, which occurs when oxygen is scarce. The reduction of minerals leaves them electrically unstable, more soluble and internally stressed and easily decomposed. It mainly occurs in [[Waterlogging (agriculture)|waterlogged]] conditions.<ref>{{cite journal |last1=Favre |first1=Fabienne |last2=Tessier |first2=Daniel |last3=Abdelmoula |first3=Mustapha |last4=Génin |first4=Jean-Marie |last5=Gates |first5=Will P. |last6=Boivin |first6=Pascal |year=2002 |title=Iron reduction and changes in cation exchange capacity in intermittently waterlogged soil |journal=European Journal of Soil Science |volume=53 |issue=2 |pages=175–83 |doi=10.1046/j.1365-2389.2002.00423.x |bibcode=2002EuJSS..53..175F |s2cid=98436639 |url=https://art1lib.org/book/5115541/2bfa4e |access-date=14 November 2021 }}</ref>

Of the above, hydrolysis and carbonation are the most effective, in particular in regions of high rainfall, temperature and physical [[erosion]].<ref>{{cite journal |last1=Riebe |first1=Clifford S. |last2=Kirchner |first2=James W. |last3=Finkel |first3=Robert C. |year=2004 |title=Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes spanning diverse climate regimes |journal=[[Earth and Planetary Science Letters]] |volume=224 |issue=3/4 |pages=547–62 |url=http://www.geog.ucsb.edu/~bodo/Geog295-Fall2012/riebe2004_mineral_weathering.pdf |doi=10.1016/j.epsl.2004.05.019 |access-date=21 November 2021 |bibcode=2004E&PSL.224..547R }}</ref> Chemical weathering becomes more effective as the surface area of the rock increases, thus is favoured by physical disintegration.<ref>{{cite web |url=http://midwaymsscience.weebly.com/uploads/8/2/9/8/8298729/section_2_-_rates_of_weathering.pdf |title=Rates of weathering |access-date=21 November 2021 |archive-date=13 June 2013 |archive-url=https://web.archive.org/web/20130613022251/http://midwaymsscience.weebly.com/uploads/8/2/9/8/8298729/section_2_-_rates_of_weathering.pdf |url-status=dead }}</ref> This stems in latitudinal and altitudinal climate gradients in [[regolith]] formation.<ref>{{cite journal |last1=Dere |first1=Ashlee L. |last2=White |first2=Timothy S. |last3=April |first3=Richard H. |last4=Reynolds |first4=Bryan |last5=Miller |first5=Thomas E. |last6=Knapp |first6=Elizabeth P. |last7=McKay |first7=Larry D. |last8=Brantley |first8=Susan L. |year=2013 |title=Climate dependence of feldspar weathering in shale soils along a latitudinal gradient |journal=[[Geochimica et Cosmochimica Acta]] |volume=122 |pages=101–26 |doi=10.1016/j.gca.2013.08.001 |url=https://booksc.eu/book/23749430/d62f8e |bibcode=2013GeCoA.122..101D |access-date=21 November 2021 }}</ref><ref>{{cite journal |last1=Kitayama |first1=Kanehiro |last2=Majalap-Lee |first2=Noreen |last3=Aiba |first3=Shin-ichiro |year=2000 |title=Soil phosphorus fractionation and phosphorus-use efficiencies of tropical rainforests along altitudinal gradients of Mount Kinabalu, Borneo |journal=[[Oecologia]] |volume=123 |issue=3 |pages=342–49 |doi=10.1007/s004420051020 |pmid=28308588 |bibcode=2000Oecol.123..342K |s2cid=20660989 |url=https://booksc.eu/book/7650890/88e945 |access-date=21 November 2021 }}</ref>

[[Saprolite]] is a particular example of a residual soil formed from the transformation of granite, metamorphic and other types of bedrock into clay minerals. Often called weathered granite, saprolite is the result of weathering processes that include: hydrolysis, chelation from organic compounds, hydration and physical processes that include freezing and thawing. The mineralogical and chemical composition of the primary bedrock material, its physical features (including [[grain size]] and degree of consolidation), and the rate and type of weathering transforms the parent material into a different mineral. The texture, pH and mineral constituents of saprolite are inherited from its parent material. This process is also called ''arenization'', resulting in the formation of sandy soils, thanks to the much higher resistance of quartz compared to other mineral components of granite (e.g., [[mica]], [[amphibole]], feldspar).<ref>{{cite journal |last1=Sequeira Braga |first1=Maria Amália |last2=Paquet |first2=Hélène |last3=Begonha |first3=Arlindo |year=2002 |title=Weathering of granites in a temperate climate (NW Portugal): granitic saprolites and arenization |journal=Catena |volume=49 |issue=1/2 |pages=41–56 |url=http://home.uevora.pt/~lopes/Artigos/23.PDF |doi=10.1016/S0341-8162(02)00017-6 |bibcode=2002Caten..49...41S |access-date=21 November 2021 }}</ref>

===Climate===
The principal climatic variables influencing soil formation are effective [[precipitation]] (i.e., precipitation minus [[evapotranspiration]]) and temperature, both of which affect the rates of chemical, physical, and biological processes.<ref>{{cite journal |last=Mosier |first=Arvin R. |year=1998 |title=Soil processes and global change |journal=Biology and Fertility of Soils |volume=27 |issue=3 |pages=221–29 |url=https://link.springer.com/content/pdf/10.1007/s003740050424.pdf |doi=10.1007/s003740050424 |bibcode=1998BioFS..27..221M |s2cid=44244791 |access-date=28 November 2021 }}</ref> Temperature and moisture both influence the organic matter content of soil through their effects on the balance between [[primary production]] and [[decomposition]]: the colder or drier the climate the lesser atmospheric carbon is fixed as organic matter while the lesser organic matter is decomposed.<ref>{{cite journal |last1=Epstein |first1=Howard E. |last2=Burke |first2=Ingrid C. |author-link2=Ingrid Burke |last3=Lauenroth |first3=William K. |year=2002 |title=Regional patterns of decomposition and primary production rates in the U.S. Great Plains |journal=[[Ecology (journal)|Ecology]] |volume=83 |issue=2 |pages=320–27 |url=https://www.researchgate.net/publication/233379719 |doi=10.2307/2680016 |jstor=2680016 |access-date=28 November 2021 }}</ref> Climate also indirectly influences soil formation through the effects of vegetation cover and biological activity, which modify the rates of chemical reactions in the soil.<ref>{{cite journal |last=Lucas |first=Yves |year=2001 |title=The role of plants in controlling rates and products of weathering: importance of biological pumping |url=https://www.researchgate.net/publication/228608786 |journal=[[Annual Review of Earth and Planetary Sciences]] |volume=29 |pages=135–63 |bibcode=2001AREPS..29..135L |doi=10.1146/annurev.earth.29.1.135 |access-date=5 December 2021}}</ref>

Climate is the dominant factor in soil formation, and soils show the distinctive characteristics of the [[climate zone]]s in which they form, with a feedback to climate through transfer of carbon stocked in soil horizons back to the atmosphere.<ref name="Davidson">{{cite journal |last1=Davidson |first1=Eric A. |last2=Janssens |first2=Ivan A. |journal=[[Nature (journal)|Nature]] |volume=440 |title=Temperature sensitivity of soil carbon decomposition and feedbacks to climate change |year=2006 |issue=7081 |pages=165‒73 |doi=10.1038/nature04514 |pmid=16525463|bibcode=2006Natur.440..165D |s2cid=4404915 |doi-access=free }}</ref> If warm temperatures and abundant water are present in the profile at the same time, the processes of weathering, [[Leaching (agriculture)|leaching]], and [[Plant development|plant growth]] will be maximized. According to the climatic determination of [[biomes]], humid climates favor the growth of trees. In contrast, grasses are the dominant native vegetation in [[Subhumid temperate climate|subhumid]] and [[Semi-arid climate|semiarid]] regions, while shrubs and brush of various kinds dominate in [[Desert climate|arid]] areas.<ref>{{cite journal |last1=Woodward |first1=F. Ian |last2=Lomas |first2=Mark R. |last3=Kelly |first3=Colleen K. |year=2004 |title=Global climate and the distribution of plant biomes |journal=[[Philosophical Transactions of the Royal Society B|Philosophical Transactions of the Royal Society of London, Series B]] |volume=359 |issue=1450 |pages=1465–76 |doi=10.1098/rstb.2004.1525 |pmc=1693431 |pmid=15519965 |url=https://www.researchgate.net/publication/8200458 |access-date=28 November 2021 }}</ref>

Water is essential for all the major chemical weathering reactions. To be effective in soil formation, water must penetrate the [[regolith]]. The seasonal rainfall distribution, evaporative losses, site [[topography]], and [[soil permeability]] interact to determine how effectively precipitation can influence soil formation. The greater the depth of water penetration, the greater the depth of weathering of the soil and its development.<ref>{{cite journal |last1=Graham |first1=Robert C. |last2=Rossi |first2=Ann M. |last3=Hubbert |first3=Kenneth R. |year=2010 |title=Rock to regolith conversion: producing hospitable substrates for terrestrial ecosystems |journal=[[Geological Society of America|GSA Today]] |volume=20 |issue=2 |pages=4–9 |doi=10.1130/GSAT57A.1 |url=https://www.geosociety.org/gsatoday/archive/20/2/pdf/i1052-5173-20-2-4.pdf |access-date=28 November 2021 }}</ref> Surplus water percolating through the soil profile transports soluble and suspended materials from the upper layers ([[eluviation]]) to the lower layers ([[illuviation]]), including clay particles<ref>{{cite journal |last=Fedoroff |first=Nicolas |year=1997 |title=Clay illuviation in Red Mediterranean soils |url=https://art1lib.org/book/17953836/4309d5 |journal=Catena |volume=28 |issue=3–4 |pages=171–89 |doi=10.1016/S0341-8162(96)00036-7 |bibcode=1997Caten..28..171F |access-date=5 December 2021 }}</ref> and [[dissolved organic matter]].<ref>{{cite journal |last1=Michalzik |first1=Beate |last2=Kalbitz |first2=Karsten |last3=Park |first3=Ji-Hyung |last4=Solinger |first4=Stephan |last5=Matzner |first5=Egbert |year=2001 |title=Fluxes and concentrations of dissolved organic carbon and nitrogen: a synthesis for temperate forests |journal=Biogeochemistry |volume=52 |issue=2 |pages=173–205 |url=https://www.researchgate.net/publication/226356840 |doi=10.1023/A:1006441620810 |bibcode=2001Biogc..52..173M |s2cid=97298438 |access-date=5 December 2021 }}</ref> It may also carry away soluble materials in the surface [[drainage]] waters. Thus, percolating water stimulates weathering reactions and helps differentiate soil horizons. 

Likewise, a deficiency of water is a major factor in determining the characteristics of soils of dry regions. Soluble salts are not leached from these soils, and in some cases they build up to levels that curtail plant<ref>{{cite journal |last=Bernstein |first=Leon |year=1975 |title=Effects of salinity and sodicity on plant growth |url=https://art1lib.org/book/15512677/2cdb0b |journal=[[Annual Review of Phytopathology]] |volume=13 |issue=1 |pages=295–312 |doi=10.1146/annurev.py.13.090175.001455  |bibcode=1975AnRvP..13..295B |access-date=5 December 2021 }}</ref> and microbial growth.<ref>{{cite journal |last1=Yuan |first1=Bing-Cheng |last2=Li |first2=Zi-Zhen |last3=Liu |first3=Hua |last4=Gao |first4=Meng |last5=Zhang |first5=Yan-Yu |year=2007 |title=Microbial biomass and activity in salt affected soils under arid conditions |journal=Applied Soil Ecology |volume=35 |issue=2 |pages=319–28 |url=https://art1lib.org/book/16525751/aa5578 |doi=10.1016/j.apsoil.2006.07.004 |bibcode=2007AppSE..35..319Y |access-date=5 December 2021 }}</ref> Soil profiles in arid and semi-arid regions are also apt to accumulate carbonates and certain types of expansive clays ([[calcrete]] or [[caliche]] horizons).<ref>{{cite journal |last=Schlesinger |first=William H. |year=1982 |title=Carbon storage in the caliche of arid soils: a case study from Arizona |journal=Soil Science |volume=133 |issue=4 |pages=247–55 |doi=10.1097/00010694-198204000-00008 |bibcode=1982SoilS.133..247S |s2cid=97632160 |url=https://www.researchgate.net/publication/249345714 |archive-url=https://web.archive.org/web/20180304054729/http://alliance.la.asu.edu/temporary/students/Phil/ArizonaCarbonStorage.pdf |url-status=live |archive-date=4 March 2018 |access-date=5 December 2021 }}</ref><ref>{{cite journal |last1=Nalbantoglu |first1=Zalihe |last2=Gucbilmez |first2=Emin |year=2001 |title=Improvement of calcareous expansive soils in semi-arid environments  |url=https://coek.info/pdf-improvement-of-calcareous-expansive-soils-in-semi-arid-environments-.html |journal=[[Journal of Arid Environments]] |volume=47 |issue=4 |pages=453–63 |doi=10.1006/jare.2000.0726 |bibcode=2001JArEn..47..453N  |access-date=5 December 2021 }}</ref> In tropical soils, when the soil has been deprived of vegetation (e.g. by [[deforestation]]) and thereby is submitted to intense evaporation, the upward [[Capillary action|capillary]] movement of water, which has dissolved iron and aluminum salts, is responsible for the formation of a superficial hard pan of [[laterite]] or [[bauxite]], respectively, which is improper for cultivation, a known case of irreversible [[soil degradation]].<ref>{{cite journal |last=Retallack |first=Gregory J. |year=2010 |title=Lateritization and bauxitization events |journal=[[Economic Geology (journal)|Economic Geology]] |volume=105 |issue=3 |pages=655–67 |url=https://www.researchgate.net/publication/247864948 |doi=10.2113/gsecongeo.105.3.655 |bibcode=2010EcGeo.105..655R |access-date=5 December 2021 }}</ref>

The direct influences of climate include:{{sfn|Donahue|Miller|Shickluna|1977|p=35}}
* A shallow accumulation of lime in low rainfall areas as [[caliche]]
* Formation of acid soils in humid areas
* Erosion of soils on steep hillsides
* Deposition of eroded materials downstream
* Very intense chemical weathering, leaching, and erosion in warm and humid regions where soil does not freeze

Climate directly affects the rate of weathering and leaching. Wind moves sand and smaller particles (dust), especially in arid regions where there is little plant cover, depositing it close to<ref>{{cite book |last1=Pye |first1=Kenneth |last2=Tsoar |first2=Haim |year=1987 |chapter=The mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern Negev, Israel |doi=10.1144/GSL.SP.1987.035.01.10 |title=Desert sediments: ancient and modern |journal=Geological Society of London, Special Publications |volume=35 |issue=1 |editor1-last=Frostick |editor1-first=Lynne |editor2-last=Reid |editor2-first=Ian |pages=139–56 |isbn=978-0-632-01905-2 |chapter-url=https://www.researchgate.net/publication/238424245 |access-date=5 December 2021 |bibcode=1987GSLSP..35..139P |s2cid=128746705 }}</ref> or far from the entrainment source.<ref>{{cite journal |last=Prospero |first=Joseph M. |year=1999 |title=Long-range transport of mineral dust in the global atmosphere: impact of African dust on the environment of the southeastern United States |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=96 |issue=7 |pages=3396–403 |doi=10.1073/pnas.96.7.3396 |pmid=10097049 |bibcode=1999PNAS...96.3396P |pmc=34280 |doi-access=free }}</ref> The type and amount of precipitation influence soil formation by affecting the movement of ions and particles through the soil, and aid in the development of different soil profiles. Soil profiles are more distinct in wet and cool climates, where organic materials may accumulate, than in wet and warm climates, where organic materials are rapidly consumed.<ref>{{cite journal |last1=Post |first1=Wilfred M. |last2=Emanuel |first2=William R. |last3=Zinke |first3=Paul J. |last4=Stangerberger |first4=Alan G. |year=1999 |title=Soil carbon pools and world life zones |url=https://art1lib.org/book/10473904/17cc99 |journal=[[Nature (journal)|Nature]] |volume=298 |issue=5870 |pages=156–59 |doi=10.1038/298156a0 |bibcode=1982Natur.298..156P |s2cid=4311653 |access-date=5 December 2021 }}</ref> The effectiveness of water in weathering parent rock material depends on seasonal and daily temperature fluctuations, which favour [[tensile stress]]es in rock minerals, and thus their mechanical disaggregation, a process called [[thermal fatigue]].<ref>{{cite journal |last1=Gómez-Heras |first1=Miguel |last2=Smith |first2=Bernard J. |last3=Fort |first3=Rafael |year=2006 |title=Surface temperature differences between minerals in crystalline rocks: implications for granular disaggregation of granites through thermal fatigue |url=https://www.academia.edu/52691323 |journal=[[Geomorphology (journal)|Geomorphology]] |volume=78 |issue=3/4 |pages=236–49 |doi=10.1016/j.geomorph.2005.12.013 |bibcode=2006Geomo..78..236G |access-date=5 December 2021 }}</ref> By the same process [[freeze-thaw]] cycles are an effective mechanism which breaks up rocks and other consolidated materials.<ref>{{cite journal |last1=Nicholson |first1=Dawn T. |last2=Nicholson |first2=Frank H. |year=2000 |title=Physical deterioration of sedimentary rocks subjected to experimental freeze–thaw weathering |journal=[[Earth Surface Processes and Landforms]] |volume=25 |issue=12 |pages=1295–307 |doi=10.1002/1096-9837(200011)25:12<1295::AID-ESP138>3.0.CO;2-E |bibcode=2000ESPL...25.1295N |url=https://art1lib.org/book/135323/a787c4 |access-date=5 December 2021 }}</ref>

===Topography===
The topography, or [[Terrain|relief]], is characterized by the inclination ([[slope]]), [[elevation]], and orientation of the terrain ([[Aspect (geography)|aspect]]). Topography determines the rate of precipitation or [[Surface runoff|runoff]] and the rate of formation or erosion of the surface [[soil profile]]. The topographical setting may either hasten or retard the work of climatic forces.<ref>{{cite journal |last1=Griffiths |first1=Robert P. |last2=Madritch |first2=Michael D. |last3=Swanson |first3=Alan K. |year=2009 |title=The effects of topography on forest soil characteristics in the Oregon Cascade Mountains (USA): implications for the effects of climate change on soil properties |journal=[[Forest Ecology and Management]] |volume=257 |issue=1 |pages=1–7 |url=https://art1lib.org/book/16811974/b4a3ea |doi=10.1016/j.foreco.2008.08.010 |bibcode=2009ForEM.257....1G |access-date=12 December 2021 |archive-date=12 December 2021 |archive-url=https://web.archive.org/web/20211212085511/https://art1lib.org/book/16811974/b4a3ea |url-status=dead }}</ref>

Steep slopes encourage rapid soil loss by erosion and allow less rainfall to enter the soil before running off and hence, little mineral deposition in lower profiles (illuviation). In semiarid regions, the lower effective rainfall on steeper slopes also results in less complete vegetative cover, so there is less plant contribution to soil formation.<ref>{{cite journal |last1=Wilcox |first1=Bradford P. |last2=Wood |first2=M. Karl |last3=Tromble |first3=John M. |year=1988 |title=Factors influencing infiltrability of semiarid mountain slopes |journal=Journal of Range Management |volume=41 |issue=3  |pages=197–206 |url=https://repository.arizona.edu/bitstream/handle/10150/645177/8240-8121-2-PB.pdf |doi=10.2307/3899167 |jstor=3899167 |hdl=10150/645177 |access-date=12 December 2021 }}</ref> For all of these reasons, steep slopes prevent the formation of soil from getting very far ahead of soil destruction. Therefore, soils on steep terrain tend to have rather shallow, poorly developed profiles in comparison to soils on nearby, more level sites.<ref>{{cite journal |last1=Liu |first1=Baoyuan |last2=Nearing |first2=Mark A. |last3=Risse |first3=L. Mark |year=1994 |title=Slope gradient effects on soil loss for steep slopes |journal=Transactions of the [[American Society of Agricultural and Biological Engineers]] |volume=37 |issue=6 |pages=1835–40 |url=https://www.researchgate.net/publication/270613706 |doi=10.13031/2013.28273 |access-date=12 December 2021 }}</ref>

Topography determines exposure to weather, fire, and other forces of man and nature. Mineral accumulations, plant nutrients, type of vegetation, vegetation growth, erosion, and water drainage are dependent on topographic relief.<ref>{{cite journal |last1=Chen |first1=Zueng-Sang |last2=Hsieh |first2=Chang-Fu |last3=Jiang |first3=Feei-Yu |last4=Hsieh |first4=Tsung-Hsin |last5=Sun |first5=I-Fang |year=1997 |title=Relations of soil properties to topography and vegetation in a subtropical rain forest in southern Taiwan |journal=[[Plant Ecology (journal)|Plant Ecology]] |volume=132 |issue=2 |pages=229–41 |url=https://www.researchgate.net/publication/227052359 |doi=10.1023/A:1009762704553 |bibcode=1997PlEco.132..229C |s2cid=2838442 |access-date=19 December 2021 }}</ref> Soils at the bottom of a hill will get more water than soils on the slopes, and soils on the slopes that face the [[sun path|sun's path]] will be drier than soils on slopes that do not.<ref>{{cite journal |last1=Hanna |first1=Abdulaziz Yalda |last2=Harlan |first2=Phillip W. |last3=Lewis |first3=David T. |year=1982 |title=Soil available water as influenced by landscape position and aspect |journal=[[Agronomy Journal]] |volume=74 |issue=6 |pages=999–1004 |url=https://art1lib.org/book/73566368/dae33c |doi=10.2134/agronj1982.00021962007400060016x |access-date=19 December 2021 |archive-date=18 August 2023 |archive-url=https://web.archive.org/web/20230818054818/https://art1lib.org/book/73566368/dae33c |url-status=dead }}</ref>

In [[Swale (landform)|swale]]s and depressions where runoff water tends to concentrate, the regolith is usually more deeply weathered, and soil profile development is more advanced.<ref>{{cite journal |last1=Graham |first1=Robert C. |last2=Daniels |first2=Raymond B. |last3=Buol |first3=Stanley W. |year=1990 |title=Soil-geomorphic relations on the Blue Ridge Front. I. Regolith types and slope processes |journal=[[Soil Science Society of America Journal]] |volume=54 |issue=5 |pages=1362–67 |url=https://art1lib.org/book/23110499/4b8c77 |doi=10.2136/sssaj1990.03615995005400050027x |bibcode=1990SSASJ..54.1362G |access-date=26 December 2021 }}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> However, in the lowest landscape positions, water may saturate the regolith to such a degree that drainage and aeration are restricted. Here, the weathering of some minerals and the decomposition of organic matter are retarded, while the loss of iron and manganese is accelerated. In such low-lying topography, special profile features characteristic of [[wetland]] soils may develop. Depressions allow the accumulation of water, minerals and organic matter, and in the extreme, the resulting soils will be [[saline marsh]]es or [[peat bog]]s.<ref>{{cite book |last=Brinson |first=Mark M. |title=A hydrogeomorphic classification for wetlands |year=1993 |publisher=[[United States Army Corps of Engineers|US Army Corps of Engineers]], [[Waterways Experiment Station]] |location=Washington, DC |url=https://erdc-library.erdc.dren.mil/jspui/bitstream/11681/6483/1/TR-WRP-DE-4.pdf |access-date=26 December 2021 }}</ref>

Recurring patterns of topography result in toposequences or [[catena (soil)|soil catenas]]. These patterns emerge from topographic differences in erosion, deposition, [[soil fertility|fertility]], [[soil moisture]], plant cover, [[soil biology]], [[fire history]], and exposure to the elements. Gravity transports water downslope, together with mineral and organic [[Solution (chemistry)|solutes]] and [[colloid]]s, increasing [[Particulates|particulate]] and base content at the foot of hills and mountains.<ref>{{cite journal |last1=Jiang |first1=Pingping |last2=Thelen |first2=Kurt D. |year=2004 |title=Effect of soil and topographic properties on crop yield in a North-Central corn–soybean cropping system |journal=[[Agronomy Journal]] |volume=96 |issue=1 |pages=252–58 |url=https://art1lib.org/book/71720754/fe8f90 |doi=10.2134/agronj2004.0252 |bibcode=2004AgrJ...96..252J |access-date=9 January 2022 }}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> However, many other factors like drainage and erosion interact with slope position, blurring its expected influence on [[crop yield]].<ref>{{cite journal |last1=Thelemann |first1=Ryan |last2=Johnson |first2=Gregg |last3=Sheaffer |first3=Craig |last4=Banerjee |first4=Sudipto |last5=Cai |first5=Haowen |last6=Wyse |first6=Donald |year=2010 |title=The effect of landscape position on biomass crop yield |journal=[[Agronomy Journal]] |volume=102 |issue=2 |pages=513–22 |url=https://www.researchgate.net/publication/240783650 |doi=10.2134/agronj2009.0058 |access-date=9 January 2022 |doi-access=free |bibcode=2010AgrJ..102..513T }}</ref>

===Organisms===
Each soil has a unique combination of microbial, plant, animal and human influences acting upon it. [[Microorganism|Microorganisms]] are particularly influential in the mineral transformations critical to the soil forming process. Additionally, some bacteria can fix atmospheric nitrogen, and some fungi are efficient at extracting deep soil [[phosphorus]] and increasing [[soil carbon]] levels in the form of [[glomalin]].<ref>{{cite journal |last1=Wang |first1=Wenjie |last2=Zhong |first2=Zhaoliang |last3=Wang |first3=Qiong |last4=Wang |first4=Humei |last5=Fu |first5=Yujie |last6=He |first6=Xingyuan |year=2017 |title=Glomalin contributed more to carbon, nutrients in deeper soils, and differently associated with climates and soil properties in vertical profiles |journal=[[Scientific Reports]] |volume=7 |issue=13003 |page=13003 |doi=10.1038/s41598-017-12731-7 |pmid=29021579 |pmc=5636888 |bibcode=2017NatSR...713003W }}</ref> Plants hold soil against erosion, and accumulated plant material build soil [[humus]] levels. Plant [[Root mucilage|root exudation]] supports microbial activity. Animals serve to decompose plant materials and mix soil through [[bioturbation]].<ref>{{cite book |last1=Van Breemen |first1=Nico |last2=Buurman |first2=Peter |title=Soil formation |year=2003 |edition=Second |publisher=[[Springer Science+Business Media|Kluwer Academic Publishers]] |location=Dordrecht, The Netherlands |url=https://fr1lib.org/book/857347/e9d4a6 |access-date=16 January 2022 }}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Soil is the most speciose (species-rich) [[ecosystem]] on Earth, but the vast majority of organisms in soil are microbes, a great many of which have not been described.<ref name="Wall2001">{{cite book |last1=Wall |first1=Diana H. |last2=Adams |first2=Gina |last3=Parsons |first3=Andrew N. |title=Soil biodiversity |series=Ecological Studies |year=2001 |volume=152 |publisher=[[Springer Publishing|Springer]] |location=New York, NY |doi=10.1007/978-1-4613-0157-8 |isbn=978-0-387-95286-4 |s2cid=45261145 |url=https://link.springer.com/content/pdf/10.1007%2F978-1-4613-0157-8.pdf |access-date=16 January 2022 }}</ref><ref name="nature2008">{{cite journal |last=Dance |first=Amber |journal=[[Nature (journal)|Nature]] |title=What lies beneath |year=2008 |volume=455 |issue=7214 |pages=724–25 |pmid=18843336 |doi=10.1038/455724a |s2cid=30863755 |url=http://www.nature.com/news/2008/081008/pdf/455724a.pdf |access-date=16 January 2022 }}</ref> There may be a population limit of around one billion cells per gram of soil, but estimates of the number of species vary widely from 50,000 per gram to over a million per gram of soil.<ref name="Gans2005">{{cite journal |last1=Gans |first1=Jason |last2=Wolinsky |first2=Murray |last3=Dunbar |first3=John |year=2005 |title=Computational improvements reveal great bacterial diversity and high metal toxicity in soil |journal=[[Science (journal)|Science]] |volume=309 |issue=5739 |pages=1387–90 |url=https://www.researchgate.net/publication/7637990 |doi=10.1126/science.1112665 |pmid=16123304 |access-date=16 January 2022 |bibcode=2005Sci...309.1387G |s2cid=130269020 }}</ref><ref name="roesch">{{cite journal |last1=Roesch |first1=Luiz F.W. |last2=Fulthorpe |first2=Roberta R. |last3=Riva |first3=Alberto |last4=Casella |first4=George |last5=Hadwin |first5=Alison K.M. |last6=Kent |first6=Angela D. |last7=Daroub |first7=Samira H. |last8=Camargo |first8=Flavio A.O. |last9=Farmerie |first9=William G. |last10=Triplett |first10=Eric W. |journal=[[The ISME Journal]] |title=Pyrosequencing enumerates and contrasts soil microbial diversity |year=2007 |volume=1 |issue=4 |pages=283–90 |pmc=2970868 |pmid=18043639 |doi=10.1038/ismej.2007.53 |bibcode=2007ISMEJ...1..283R |url=https://art1lib.org/book/10595442/a9ae88 |access-date=16 January 2022 }}</ref> The number of organisms and species can vary widely according to soil type, location, and depth.<ref name="nature2008"/><ref name="roesch"/>

Plants, animals, fungi, bacteria and humans affect soil formation (see [[Soil Biomantle|soil biomantle]] and [[stonelayer]]). Soil animals, including fauna and [[soil mesofauna]], mix soils as they form [[burrow]]s and [[Porosity|pores]], allowing moisture and gases to move about, a process called bioturbation.<ref>{{cite journal |last1=Meysman |first1=Filip J.R. |last2=Middelburg |first2=Jack J. |last3=Heip |first3=Carlo H.R. |year=2006 |title=Bioturbation: a fresh look at Darwin's last idea |journal=[[Trends in Ecology and Evolution]] |volume=21 |issue=12 |pages=688–95 |url=https://www.academia.edu/13631880 |doi=10.1016/j.tree.2006.08.002 |pmid=16901581 |bibcode=2006TEcoE..21..688M |access-date=23 January 2022 }}</ref> In the same way, plant roots penetrate soil horizons and open channels upon decomposition.<ref>{{cite journal |last1=Williams |first1=Stacey M. |last2=Weil |first2=Ray R. |year=2004 |title=Crop cover root channels may alleviate soil compaction effects on soybean crop |journal=[[Soil Science Society of America Journal]] |volume=68 |issue=4 |pages=1403–09 |url=https://www.researchgate.net/publication/240789602 |doi=10.2136/sssaj2004.1403 |access-date=23 January 2022 |bibcode=2004SSASJ..68.1403W }}</ref> Plants with deep [[taproot]]s can penetrate many metres through the different soil layers to bring up nutrients from deeper in the profile.<ref>{{cite journal |last=Lynch |first=Jonathan |year=1995 |title=Root architecture and plant productivity |journal=[[Plant Physiology (journal)|Plant Physiology]] |url=https://art1lib.org/book/64045845/0c6b21 |volume=109 |issue=1 |pages=7–13 |doi=10.1104/pp.109.1.7 |pmid=12228579 |pmc=157559 |access-date=23 January 2022 }}</ref> Plants have fine roots that excrete organic compounds (sugars, organic acids, mucilage), slough off cells (in particular at their tip), and are easily decomposed, adding organic matter to soil, a process called ''rhizodeposition''.<ref>{{cite journal |last=Nguyen |first=Christophe |year=2003 |title=Rhizodeposition of organic C by plants: mechanisms and controls |journal=[[Agronomy for Sustainable Development|Agronomie]] |volume=23 |issue=5/6 |pages=375–96 |url=https://hal.archives-ouvertes.fr/file/index/docid/886190/filename/hal-00886190.pdf |doi=10.1051/agro:2003011 |bibcode=2003AgSD...23..375N |s2cid=55101606 |access-date=23 January 2022 }}</ref> 

Microorganisms, including fungi and bacteria, effect chemical exchanges between roots and soil and act as a reserve of nutrients in a soil biological hotspot called [[rhizosphere]].<ref>{{cite thesis |last1=Widmer |first1=Franco |last2=Pesaro |first2=Manuel |last3=Zeyer |first3=Josef |last4=Blaser |first4=Peter |year=2000 |chapter=Preferential flow paths: biological 'hot spots' in soils |doi=10.3929/ethz-a-004036424 |title=Highways through the soil: properties of preferential flow paths and transport of reactive compounds |editor-first=Maya |editor-last=Bundt |publisher=[[ETH]] Library |location=Zurich |pages=53–75 |chapter-url=https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/144808/eth-23683-02.pdf#page=65 |access-date=23 January 2022 |hdl=20.500.11850/144808 }}</ref> The growth of roots through the soil stimulates microbial populations, stimulating in turn the activity of their predators (notably [[amoeba]]), thereby increasing the [[mineralization (soil science)|mineralization rate]], and in last turn root growth, a positive feedback called the soil [[microbial loop]].<ref>{{cite journal |last=Bonkowski |first=Michael |year=2004 |title=Protozoa and plant growth: the microbial loop in soil revisited |journal=[[New Phytologist]] |volume=162 |issue=3 |pages=617–31 |doi=10.1111/j.1469-8137.2004.01066.x |pmid=33873756 |doi-access=free |bibcode=2004NewPh.162..617B }}</ref> Out of root influence, in the [[bulk soil]] most bacteria are in a quiescent stage, forming micro-[[aggregate (composite)|aggregates]], i.e. [[mucilage|mucilaginous]] colonies to which clay particles are glued, offering them a protection against [[desiccation]] and predation by soil [[microfauna]] ([[bacteriophagous]] [[protozoa]] and [[nematodes]]).<ref>{{cite journal |last1=Six |first1=Johan |last2=Bossuyt |first2=Heleen |last3=De Gryze |first3=Steven |last4=Denef |first4=Karolien |year=2004 |title=A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics |journal=Soil and Tillage Research |volume=79 |issue=1 |pages=7–31 |url=https://www.researchgate.net/publication/222426695 |doi=10.1016/j.still.2004.03.008 |bibcode=2004STilR..79....7S |access-date=23 January 2022 }}</ref> Microaggregates (20–250&nbsp;μm) are ingested by soil mesofauna and fauna, and bacterial bodies are partly or totally digested in their guts.<ref>{{cite journal |last1=Saur |first1=Étienne |last2=Ponge |first2=Jean-François |year=1988 |title=Alimentary studies on the collembolan Paratullbergia callipygos using transmission electron microscopy |journal=Pedobiologia |volume=31 |issue=5/6 |pages=355–79 |doi=10.1016/S0031-4056(23)02274-6 |bibcode=1988Pedob..31..355S |url=https://www.academia.edu/52490540 |access-date=23 January 2022 }}</ref>

Humans impact soil formation by removing vegetation cover through [[tillage]], application of [[biocide]]s, fire and leaving soils bare. This can lead to erosion, waterlogging, lateritization or [[Podsolisation|podzolization]] (according to climate and topography).<ref>{{cite book |last=Oldeman |first=L. Roel |date=1992 |chapter=Global extent of soil degradation |title=ISRIC Bi-Annual Report 1991/1992 |publisher=[[ISRIC]] |location=Wageningen, The Netherlands |pages=19–36 |chapter-url=https://library.wur.nl/WebQuery/wurpubs/fulltext/299739 |access-date=23 January 2022 }}</ref> Tillage mixes the different soil layers, restarting the soil formation process as less weathered material is mixed with the more developed upper layers, resulting in net increased rate of mineral weathering.<ref>{{cite journal |last1=Karathanasis |first1=Anastasios D. |last2=Wells |first2=Kenneth L. |year=2004 |title=A comparison of mineral weathering trends between two management systems on a catena of loess-derived soils |journal=[[Soil Science Society of America Journal]] |volume=53 |issue=2 |pages=582–88 |url=https://art1lib.org/book/23110084/bee731 |doi=10.2136/sssaj1989.03615995005300020047x |bibcode=1989SSASJ..53..582K |access-date=23 January 2022 }}</ref>

Earthworms, ants, termites, moles, gophers, as well as some millipedes and tenebrionid beetles, mix the soil as they burrow, significantly affecting soil formation.<ref name="Lee1991">{{cite journal |last1=Lee |first1=Kenneth Ernest |last2=Foster |first2=Ralph C. |year=2003 |title=Soil fauna and soil structure |journal=[[Australian Journal of Soil Research]] |volume=29 |issue=6 |pages=745–75 |doi=10.1071/SR9910745 |url=https://booksc.eu/book/23597797/35b543 |access-date=30 January 2022 }}</ref> Earthworms ingest soil particles and organic residues, enhancing the availability of plant nutrients in the material that passes through their bodies.<ref>{{cite journal |last=Scheu |first=Stefan |year=2003 |title=Effects of earthworms on plant growth: patterns and perspectives |journal=Pedobiologia |volume=47 |issue=5/6 |pages=846–56  |doi=10.1078/0031-4056-00270 |url=https://www.researchgate.net/publication/263041521 |access-date=30 January 2022 }}</ref> They aerate and stir the soil and create stable soil aggregates, after having disrupted links between soil particles during the intestinal transit of ingested soil,<ref>{{cite journal |last1=Zhang |first1=Haiquan |last2=Schrader |first2=Stefan |year=1993 |title=Earthworm effects on selected physical and chemical properties of soil aggregates |journal=Biology and Fertility of Soils |volume=15 |issue=3 |pages=229–34 |doi=10.1007/BF00361617 |bibcode=1993BioFS..15..229Z |s2cid=24151632 |url=https://booksc.eu/book/5958409/e30980 |access-date=30 January 2022 }}</ref> thereby assuring ready infiltration of water.<ref>{{cite journal |last1=Bouché |first1=Marcel B. |last2=Al-Addan |first2=Fathel |year=1997 |title=Earthworms, water infiltration and soil stability: some new assessments |journal=[[Soil Biology and Biochemistry]] |volume=29 |issue=3/4 |pages=441–52 |doi=10.1016/S0038-0717(96)00272-6 |bibcode=1997SBiBi..29..441B |url=https://booksc.eu/book/17640626/e68038 |access-date=30 January 2022 }}</ref> As ants and termites build mounds, earthworms transport soil materials from one horizon to another.<ref>{{cite journal |last=Bernier |first=Nicolas |year=1998 |title=Earthworm feeding activity and development of the humus profile |journal=Biology and Fertility of Soils |volume=26 |issue=3 |pages=215–23 |doi=10.1007/s003740050370 |bibcode=1998BioFS..26..215B |s2cid=40478203 |url=https://www.academia.edu/34816078 |access-date=30 January 2022 }}</ref> Other important functions are fulfilled by earthworms in the soil ecosystem, in particular their intense [[mucus]] production, both within the intestine and as a lining in their galleries,<ref>{{cite journal |last=Scheu |first=Stefan |year=1991 |title=Mucus excretion and carbon turnover of endogeic earthworms |journal=Biology and Fertility of Soils |volume=12 |issue=3 |pages=217–20 |url=https://www.researchgate.net/publication/226748808 |doi=10.1007/BF00337206 |bibcode=1991BioFS..12..217S |s2cid=21931989 |access-date=30 January 2022 }}</ref> exert a [[Organic matter|priming effect]] on soil microflora,<ref>{{cite journal |last=Brown |first=George G. |year=1995 |title=How do earthworms affect microfloral and faunal community diversity? |journal=[[Plant and Soil]] |volume=170 |issue=1 |pages=209–31 |doi=10.1007/BF02183068 |bibcode=1995PlSoi.170..209B |s2cid=10254688 |url=https://booksc.eu/book/6863534/05b1df |access-date=30 January 2022 }}</ref> giving them the status of [[ecosystem engineer]]s, which they share with ants and termites.<ref>{{cite journal |last1=Jouquet |first1=Pascal |last2=Dauber |first2=Jens |last3=Lagerlöf |first3=Jan |last4=Lavelle |first4=Patrick |last5=Lepage |first5=Michel |year=2006 |title=Soil invertebrates as ecosystem engineers: intended and accidental effects on soil and feedback loops |journal=Applied Soil Ecology |volume=32 |issue=2 |pages=153–64 |url=https://www.academia.edu/50439505 |doi=10.1016/j.apsoil.2005.07.004 |bibcode=2006AppSE..32..153J |access-date=30 January 2022 }}</ref>

In general, the mixing of the soil by the activities of animals, sometimes called [[Perturbation (geology)|pedoturbation]], tends to undo or counteract the tendency of other soil-forming processes that create distinct horizons.<ref>{{cite journal |last1=Bohlen |first1=Patrick J. |last2=Scheu |first2=Stefan |last3=Hale |first3=Cindy M. |last4=McLean |first4=Mary Ann |last5=Migge |first5=Sonja |last6=Groffman |first6=Peter M. |last7=Parkinson |first7=Dennis |year=2004 |title=Non-native invasive earthworms as agents of change in northern temperate forests |journal=[[Frontiers in Ecology and the Environment]] |volume=2 |issue=8 |pages=427–35 |url=https://www.researchgate.net/publication/289148663 |doi=10.2307/3868431 |access-date=30 January 2022 |jstor=3868431 }}</ref> Termites and ants may also retard soil profile development by denuding large areas of soil around their nests, leading to increased loss of soil by erosion.<ref>{{cite journal |last1=De Bruyn |first1=Lisa Lobry |last2=Conacher |first2=Arthur J. |year=1990 |title=The role of termites and ants in soil modification: a review |journal=[[Australian Journal of Soil Research]] |volume=28 |issue=1 |pages=55–93 |url=https://www.researchgate.net/publication/248884324 |doi=10.1071/SR9900055 |bibcode=1990SoilR..28...55D |access-date=30 January 2022 }}</ref> Large animals such as gophers, moles, and prairie dogs bore into the lower soil horizons, bringing materials to the surface.<ref>{{cite web |url=https://ufdc.ufl.edu/UFE0017403/00001/pdf |last=Kinlaw |first=Alton Emory |title=Burrows of semi-fossorial vertebrates in upland communities of Central Florida: their architecture, dispersion and ecological consequences |pages=19–45 |year=2006 |access-date=30 January 2022 }}</ref> Their tunnels are often open to the surface, encouraging the movement of water and air into the subsurface layers. In localized areas, they enhance mixing of the lower and upper horizons by creating and later refilling the tunnels. Old animal burrows in the lower horizons often become filled with soil material from the overlying A horizon, creating profile features known as ''crotovinas''.<ref>{{cite book |last=Borst |first=George |date=1968 |chapter=The occurrence of crotovinas in some southern California soils |title=Transactions of the 9th International Congress of Soil Science, Adelaide, Australia, August 5–15, 1968 |volume=2 |publisher=[[Angus & Robertson]] |location=Sydney, Australia |pages=19–27 |url=https://www.iuss.org/index.php?rex_media_type=download&rex_media_file=9th_international_congress_of_soil_science_transactions_volume_ii_compressed.pdf |access-date=30 January 2022 }}</ref>

Vegetation impacts soils in numerous ways. It can prevent erosion caused by excessive rain that might result from surface runoff.<ref>{{cite journal |last1=Gyssels |first1=Gwendolyn |last2=Poesen |first2=Jean |last3=Bochet |first3=Esther |last4=Li |first4=Yong |year=2005 |title=Impact of plant roots on the resistance of soils to erosion by water: a review |journal=[[Progress in Physical Geography]] |volume=29 |issue=2 |pages=189–217 |url=https://art1lib.org/book/23315291/89ee50 |doi=10.1191/0309133305pp443ra |bibcode=2005PrPG...29..189G |s2cid=55243167 |access-date=6 February 2022 }}</ref> Plants shade soils, keeping them cooler<ref>{{cite journal |last1=Balisky |first1=Allen C. |last2=Burton |first2=Philip J. |year=1993 |title=Distinction of soil thermal regimes under various experimental vegetation covers |journal=[[Canadian Journal of Soil Science]] |volume=73 |issue=4 |pages=411–20 |doi=10.4141/cjss93-043  |doi-access=free |bibcode=1993CaJSS..73..411B }}</ref> and slowing evaporation of [[soil moisture]].<ref>{{cite journal |last1=Marrou |first1=Hélène |last2=Dufour |first2=Lydie |last3=Wery |first3=Jacques |year=2013 |title=How does a shelter of solar panels influence water flows in a soil-crop system? |journal=European Journal of Agronomy |volume=50 |pages=38–51 |doi=10.1016/j.eja.2013.05.004 |bibcode=2013EuJAg..50...38M |url=https://art1lib.org/book/25051533/5113e5 |access-date=6 February 2022 }}</ref> Conversely, by way of [[transpiration]], plants can cause soils to lose moisture, resulting in complex and highly variable relationships between [[leaf area index]] (measuring light interception) and moisture loss: more generally plants prevent soil from [[desiccation]] during driest months while they dry it during moister months, thereby acting as a buffer against strong moisture variation.<ref>{{cite journal |last1=Heck |first1=Pamela |last2=Lüthi |first2=Daniel |last3=Schär |first3=Christoph |year=1999 |title=The influence of vegetation on the summertime evolution of European soil moisture |journal=Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere |volume=24 |issue=6 |pages=609–14 |url=https://art1lib.org/book/14341652/1fc870 |doi=10.1016/S1464-1909(99)00052-0 |bibcode=1999PCEB...24..609H |access-date=6 February 2022 }}</ref> Plants can form new chemicals that can break down minerals, both directly<ref>{{cite journal |last=Jones |first=David L. |year=1998 |title=Organic acids in the rhizospere: a critical review |journal=[[Plant and Soil]] |volume=205 |issue=1 |pages=25–44 |url=https://art1lib.org/book/10990607/f36bb8 |doi=10.1023/A:1004356007312 |bibcode=1998PlSoi.205...25J |s2cid=26813067 |access-date=6 February 2022 }}</ref> and indirectly through [[Mycorrhiza|mycorrhizal]] fungi<ref name="Landeweert2001" /> and rhizosphere bacteria,<ref>{{cite journal |last1=Calvaruso |first1=Christophe |last2=Turpault |first2=Marie-Pierre |last3=Frey-Klett |first3=Pascal |year=2006 |title=Root-associated bacteria contribute to mineral weathering and to mineral nutrition in trees: a budgeting analysis |journal=[[Applied and Environmental Microbiology]] |volume=72 |issue=2 |pages=1258–66  |doi=10.1128/AEM.72.2.1258-1266.2006 |pmid=16461674 |pmc=1392890 |bibcode=2006ApEnM..72.1258C }}</ref> and improve the soil structure.<ref>{{cite journal |last1=Angers |first1=Denis A. |last2=Caron |first2=Jean |year=1998 |title=Plant-induced changes in soil structure: processes and feedbacks |journal=Biogeochemistry |volume=42 |issue=1 |pages=55–72 |url=https://www.researchgate.net/publication/226938344 |doi=10.1023/A:1005944025343 |bibcode=1998Biogc..42...55A |s2cid=94249645 |access-date=6 February 2022 }}</ref> The type and amount of vegetation depend on climate, topography, soil characteristics and biological factors, mediated or not by human activities.<ref>{{cite journal |last1=Dai |first1=Shengpei |last2=Zhang |first2=Bo |last3=Wang |first3=Haijun |last4=Wang |first4=Yamin |last5=Guo |first5=Lingxia |last6=Wang |first6=Xingmei |last7=Li |first7=Dan |year=2011 |title=Vegetation cover change and the driving factors over northwest China |journal=Journal of Arid Land |volume=3 |issue=1 |pages=25–33 |url=https://www.researchgate.net/publication/228841309 |doi=10.3724/SP.J.1227.2011.00025 |doi-broken-date=11 November 2024 |access-date=6 February 2022 |doi-access=free |bibcode=2011JArL....3...25S }}</ref><ref>{{cite journal |last1=Vogiatzakis |first1=Ioannis |last2=Griffiths |first2=Geoffrey H. |last3=Mannion |first3=Antoinette M. |year=2003 |title=Environmental factors and vegetation composition, Lefka Ori Massif, Crete, S. Aegean |journal=[[Global Ecology and Biogeography]] |volume=12 |issue=2 |pages=131–46 |doi=10.1046/j.1466-822X.2003.00021.x  |url=https://art1lib.org/book/60423128/b47af0 |access-date=6 February 2022 |doi-access=free |bibcode=2003GloEB..12..131V }}</ref> Soil factors such as density, depth, chemistry, pH, temperature and moisture greatly affect the type of plants that can grow in a given location. Dead plants and fallen leaves and stems begin their decomposition on the surface. There, organisms feed on them and mix the organic material with the upper soil layers; these added organic compounds become part of the soil formation process.<ref>{{cite journal |last1=Brêthes |first1=Alain |last2=Brun |first2=Jean-Jacques |last3=Jabiol |first3=Bernard |last4=Ponge |first4=Jean-François |last5=Toutain |first5=François |year=1995 |title=Classification of forest humus forms: a French proposal |journal=Annales des Sciences Forestières |volume=52 |issue=6 |pages=535–46 |doi=10.1051/forest:19950602 |doi-access=free }}</ref>

The influence of humans, and by association, fire, are state factors placed within the organisms state factor.<ref>{{cite journal |url=https://art1lib.org/book/58287444/7c8785 |title=The place of humans in the state factor theory of ecosystems and their soils |last1=Amundson |first1=Ronald |last2=Jenny |first2=Hans |year=1991 |journal=Soil Science |volume=151 |issue=1 |pages=99–109 |doi=10.1097/00010694-199101000-00012 |bibcode=1991SoilS.151...99A |s2cid=95061311 |access-date=13 February 2022 }}</ref> Humans can import or extract nutrients and energy in ways that dramatically change soil formation. Accelerated soil erosion from [[overgrazing]], and [[Pre-Columbian]] [[terraforming]] the Amazon basin resulting in ''[[terra preta]]'' are two examples of the effects of human management.<ref>{{cite journal |last1=Ponge |first1=Jean-François |last2=Topoliantz |first2=Stéphanie |year=2005 |title=Charcoal consumption and casting activity by Pontoscolex corethurus (Glossoscolecidae) |url=https://www.researchgate.net/publication/44922028 |journal=Applied Soil Ecology |volume=28 |issue=3 |pages=217–24 |doi=10.1016/j.apsoil.2004.08.003 |bibcode=2005AppSE..28..217T |access-date=20 February 2022}}</ref>

It is believed that [[Native Americans in the United States|Native Americans]] regularly set fires to maintain several large areas of [[prairie]] grasslands in [[Indiana]] and [[Michigan]], although climate and mammalian [[Grazing (behaviour)|grazers]] (e.g. [[bisons]]) are also advocated to explain the maintenance of the [[Great Plains]] of North America.<ref>{{cite journal |last=Anderson |first=Roger C. |year=2006 |title=Evolution and origin of the Central Grassland of North America: climate, fire, and mammalian grazers |journal=[[Journal of the Torrey Botanical Society]] |volume=133 |issue=4 |pages=626–47 |url=https://www.academia.edu/6131302 |doi=10.3159/1095-5674(2006)133[626:EAOOTC]2.0.CO;2 |s2cid=13709954 |access-date=13 February 2022 |doi-access=free }}</ref> In more recent times, human destruction of natural vegetation and subsequent tillage of the soil for [[crop]] production has abruptly modified soil formation.<ref>{{cite journal |last1=Burke |first1=Ingrid C. |last2=Yonker |first2=Caroline M. |last3=Parton |first3=William J. |last4=Cole |first4=C. Vernon |last5=Flach |first5=Klaus |last6=Schimel |first6=David S. |year=1989 |title=Texture, climate, and cultivation effects on soil organic matter content in U.S. grassland soils |journal=[[Soil Science Society of America Journal]] |volume=53 |issue=3 |pages=800–05 |url=https://www.researchgate.net/publication/233209856 |doi=10.2136/sssaj1989.03615995005300030029x |access-date=13 February 2022 |bibcode=1989SSASJ..53..800B }}</ref> Likewise, irrigating soil in an arid region drastically influences soil-forming factors,<ref>{{cite journal |last1=Lisetskii |first1=Fedor N. |last2=Pichura |first2=Vitalii I. |year=2016 |title=Assessment and forecast of soil formation under irrigation in the steppe zone of Ukraine |journal=Russian Agricultural Sciences |volume=42 |issue=2 |pages=155–59 |url=http://dspace.bsu.edu.ru/bitstream/123456789/16324/1/Lisetskii_Assessment_Forecast_16_D.pdf |doi=10.3103/S1068367416020075 |bibcode=2016RuAgS..42..155L |s2cid=43356998 |access-date=13 February 2022 }}</ref> as does adding fertilizer and lime to soils of low fertility.<ref>{{cite web |url=https://stud.epsilon.slu.se/3263/1/schon_m_110919.pdf |last=Schön |first=Martina |title=Impact of N fertilization on subsoil properties: soil organic matter and aggregate stability |year=2011 |access-date=13 February 2022 }}</ref>

Distinct ecosystems produce distinct soils, sometimes in easily observable ways. For example, three species of [[land snail]]s in the genus ''[[Euchondrus]]'' in the [[Negev desert]] are noted for eating [[lichen]]s growing under the surface [[limestone]] rocks and slabs ([[endolithic]] lichens). The grazing activity of these ecosystem engineers disrupts the limestone, resulting in the weathering and the subsequent formation of soil.<ref name="Odling-Smee 2003">{{cite book |last1=Odling-Smee |first1=F. John |last2=Laland |first2=Kevin N. |last3=Feldman |first3=Marcus W. |year=2003 |chapter=Introduction |title=Niche construction: the neglected process in evolution |pages=7–8 |publisher=[[Princeton University Press]] |location=Princeton, New Jersey |isbn=978-0691044378 |chapter-url=https://fr.art1lib.org/book/79836470/bdd556 |doi=10.1515/9781400847266 |access-date=20 February 2022 |archive-date=17 June 2006 |archive-url=https://web.archive.org/web/20060617221931/http://www.pupress.princeton.edu/chapters/i7691.pdf |url-status=live }}</ref> They have a significant effect on the region: the population of snails is estimated to process between 0.7 and 1.1 metric ton per hectare per year of limestone in the Negev desert.<ref name="Odling-Smee 2003" />

The effects of ancient ecosystems are not as easily observed, and this challenges the understanding of soil formation. For example, the [[chernozem]]s of the North American tallgrass prairie have a humus fraction nearly half of which is [[charcoal]]. This outcome was not anticipated because the antecedent prairie [[fire ecology]] capable of producing these distinct deep rich black soils is not easily observed.<ref>{{cite journal |last1=Ponomarenko |first1=Elena V. |last2=Anderson |first2=Darwin W. |title=Importance of charred organic matter in Black Chernozem soils of Saskatchewan |year=2001 |journal=[[Canadian Journal of Soil Science]] |volume=81 |issue=3 |pages=285–297 |url=https://cdnsciencepub.com/doi/pdf/10.4141/S00-075 |quote=The present paradigm views humus as a system of heteropolycondensates, largely produced by the soil microflora, in varying associations with clay (Anderson 1979). Because this conceptual model, and simulation models rooted within the concept, do not accommodate a large char component, a considerable change in conceptual understanding (a paradigm shift) appears imminent. |doi=10.4141/S00-075 |bibcode=2001CaJSS..81..285P |access-date=20 February 2022 }}</ref>

===Time===
Time is a factor in the interactions of all the above.<ref name="Jenny1941"/> While a mixture of sand, silt and clay constitute the [[Soil texture|texture]] of a soil and the [[Particle aggregation|aggregation]] of those components produces [[ped]]s, the development of a distinct [[B horizon]] marks the development of a soil or pedogenesis.<ref>{{cite journal |last1=Bormann |first1=Bernard T. |last2=Spaltenstein |first2=Henri |last3=McClellan |first3=Michael H. |last4=Ugolini |first4=Fiorenzo C. |last5=Cromack |first5=Kermit Jr |last6=Nay |first6=Stephan M. |year=1995 |title=Rapid soil development after windthrow disturbance in pristine forests |journal=[[Journal of Ecology]] |volume=83 |issue=5 |pages=747–57 |url=http://www.fsl.orst.edu/ltep/Reprints_files/Bormann%20JE1995%20windthrow%20chrono.pdf |access-date=27 February 2022 |doi=10.2307/2261411 |jstor=2261411 |bibcode=1995JEcol..83..747B |s2cid=85818050 }}</ref> With time, soils will evolve features that depend on the interplay of the prior listed soil-forming factors.<ref name="Jenny1941"/> It takes decades<ref>{{cite journal |last1=Crocker |first1=Robert L. |last2=Major |first2=Jack |year=1955 |title=Soil development in relation to vegetation and surface age at Glacier Bay, Alaska |journal=[[Journal of Ecology]] |volume=43 |issue=2 |pages=427–48 |url=https://fr.art1lib.org/book/46429686/e6dd28 |doi=10.2307/2257005 |access-date=27 February 2022 |jstor=2257005 |bibcode=1955JEcol..43..427C |archive-url=https://web.archive.org/web/20170925035329/http://www.britishecologicalsociety.org/100papers/100_Ecological_Papers/100_Influential_Papers_017.pdf |archive-date=25 September 2017 |url-status=live }}</ref> to several thousand years for a soil to develop a profile,<ref name="Crews1995">{{cite journal |last1=Crews |first1=Timothy E. |last2=Kitayama |first2=Kanehiro |last3=Fownes |first3=James H. |last4=Riley |first4=Ralph H. |last5=Herbert |first5=Darrell A. |last6=Mueller-Dombois |first6=Dieter |last7=Vitousek |first7=Peter M. |year=1995 |title=Changes in soil phosphorus and ecosystem dynamics along a long term chronosequence in Hawaii |journal=[[Ecology (journal)|Ecology]] |volume=76 |issue=5 |pages=1407–24 |url=https://www.researchgate.net/publication/259671947 |doi=10.2307/1938144 |access-date=27 February 2022 |jstor=1938144 }}</ref> although the notion of soil development has been criticized, soil being in a constant state-of-change under the influence of fluctuating soil-forming factors.<ref name="Huggett1998">{{cite journal |last=Huggett |first=Richard J. |year=1998 |title=Soil chronosequences, soil development, and soil evolution: a critical review |journal=[[Catena (soil)|Catena]] |volume=32 |issue=3/4 |pages=155–72 |doi=10.1016/S0341-8162(98)00053-8 |bibcode=1998Caten..32..155H |url=https://www.academia.edu/2116704 |access-date=27 February 2022  }}</ref> That time period depends strongly on climate, parent material, relief, and biotic activity.{{sfn|Simonson|1957|pp=20–21}}{{sfn|Donahue|Miller|Shickluna|1977|p=26}} For example, recently deposited material from a flood exhibits no soil development as there has not been enough time for the material to form a structure that further defines soil.<ref>{{cite journal |last1=Craft |first1=Christopher |last2=Broome |first2=Stephen |last3=Campbell |first3=Carlton |year=2002 |title=Fifteen years of vegetation and soil development after brackish-water marsh creation |journal=[[Restoration Ecology]] |volume=10 |issue=2 |pages=248–58 |url=https://fr.art1lib.org/book/5257969/1523d7 |doi=10.1046/j.1526-100X.2002.01020.x |bibcode=2002ResEc..10..248C |s2cid=55198244 |access-date=27 February 2022 |archive-url=https://web.archive.org/web/20170810105223/http://www.marianhs.org/userfiles/1086/Classes/25998/IU%20paper%20NC%20marsh%20restoration.pdf |archive-date=10 August 2017 |url-status=live }}</ref> The original soil surface is buried, and the formation process must begin anew for this deposit. Over time the soil will develop a profile that depends on the intensities of biota and climate. While a soil can achieve relative stability of its properties for extended periods,<ref name="Crews1995"/> the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion.<ref>{{cite book |last1=Shipitalo |first1=Martin J. |last2=Le Bayon |first2=Renée-Claire |year=2004 |chapter=Chapter 10: Quantifying the effects of earthworms on soil aggregation and porosity |doi=10.1201/9781420039719 |title=Earthworm ecology |edition=2nd |editor-first=Clive A. |editor-last=Edwards |publisher=[[CRC Press]] |location=Boca Raton, Florida |pages=183–200 |isbn=978-1-4200-3971-9 |url=http://doc.rero.ch/record/17435/files/Shipitalo_Martin_-_Quantifying_the_Effects_of_Earthworms_20100310.pdf |chapter-url=https://www.researchgate.net/publication/41844767 |access-date=27 February 2022 }}</ref> Despite the inevitability of [[soil retrogression and degradation]], most soil cycles are long.<ref name="Crews1995"/>

Soil-forming factors continue to affect soils during their existence, even on stable landscapes that are long-enduring, some for millions of years.<ref name="Crews1995"/> Materials are deposited on top<ref>{{cite journal |last1=He |first1=Changling |last2=Breuning-Madsen |first2=Henrik |last3=Awadzi |first3=Theodore W. |year=2007 |title=Mineralogy of dust deposited during the Harmattan season in Ghana |journal=[[Danish Journal of Geography|Geografisk Tidsskrift]] |volume=107 |issue=1 |pages=9–15 |doi=10.1080/00167223.2007.10801371 |bibcode=2007GeTid.107....9H |citeseerx=10.1.1.469.8326 |s2cid=128479624 |url=https://www.researchgate.net/publication/258240253 |access-date=27 February 2022 }}</ref> or are blown or washed from the surface.<ref>{{cite journal |last1=Pimentel |first1=David |last2=Harvey |first2=Celia |last3=Resosudarmo |first3=Pradnja |last4=Sinclair |first4=Kevin |last5=Kurz |first5=D. |last6=McNair |first6=M. |last7=Crist |first7=S. |last8=Shpritz |first8=Lisa |last9=Fitton |first9=L. |last10=Saffouri |first10=R. |last11=Blair |first11=R. |year=1995 |title=Environmental and economic cost of soil erosion and conservation benefits |journal=[[Science (journal)|Science]] |volume=267 |issue=5201 |pages=1117–23 |url=https://www.academia.edu/9512072 |doi=10.1126/science.267.5201.1117 |access-date=27 February 2022 |bibcode=1995Sci...267.1117P |pmid=17789193 |s2cid=11936877 |archive-url=https://web.archive.org/web/20161213065558/http://www.rachel.org/files/document/Environmental_and_Economic_Costs_of_Soil_Erosi.pdf |archive-date=13 December 2016 |url-status=live }}</ref> With additions, removals and alterations, soils are always subject to new conditions. Whether these are slow or rapid changes depends on climate, topography and biological activity.<ref>{{cite journal |last1=Wakatsuki |first1=Toshiyuki |last2=Rasyidin |first2=Azwar |year=1992 |title=Rates of weathering and soil formation |journal=Geoderma |volume=52 |issue=3/4 |pages=251–63 |url=http://kinki-ecotech.jp/download/WakatsukiRasydin1992Geoderma.pdf |doi=10.1016/0016-7061(92)90040-E |access-date=27 February 2022 |bibcode=1992Geode..52..251W }}</ref>

Time as a soil-forming factor may be investigated by studying soil [[chronosequence]]s, in which soils of different ages but with minor differences in other soil-forming factors can be compared.<ref name="Huggett1998"/> [[Paleosol]]s are soils formed during previous soil forming conditions.

==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]]-->
==Example==
An example of the evolution of soils in prehistoric [[lake beds]] is in the [[Makgadikgadi Pan]]s of the [[Kalahari Desert]], where a change in an ancient river course led to millennia of salinity buildup and formation of [[calcrete]]s and [[silcrete]]s.<ref>{{cite web |last=Hogan |first=C. Michael |year=2008 |url=https://www.megalithic.co.uk/article.php?sid=22373 |title=Makgadikgadi: ancient Village or settlement in Botswana |website=The Megalithic Portal |access-date=20 March 2022 }}</ref>

==Notes==
{{Reflist}}

== References ==
{{Scholia}}
* Stanley W. Buol, F.D. Hole and R.W. McCracken. 1997. Soil Genesis and Classification, 4th ed. Iowa State Univ. Press, Ames {{ISBN|0-8138-2873-2}}
* C. Michael Hogan. 2008. ''Makgadikgadi'', The Megalithic Portal, ed. A. Burnham [http://www.megalithic.co.uk/article.php?sid=22373&mode=&order=0]
* Francis D. Hole and J.B. Campbell. 1985. Soil landscape analysis. Totowa Rowman & Allanheld, 214 p. {{ISBN|0-86598-140-X}}
* Hans Jenny. 1994. [https://web.archive.org/web/20130225050838/http://soilandhealth.org/01aglibrary/010159.Jenny.pdf Factors of Soil Formation.] A System of Quantitative Pedology. New York: Dover Press. (Reprint, with foreword by R. Amundson, of the 1941 McGraw-Hill publication). pdf file format.
* Ben van der Pluijm et al. 2005. [http://www.globalchange.umich.edu/globalchange1/current/lectures/soils/soils.html Soils, Weathering, and Nutrients] from the Global Change 1 Lectures. University of Michigan. Url last accessed on 2007-03-31

{{Soil science topics}}
{{Geologic Principles}}
{{Authority control}}

[[Category:Pedology]]
[[Category:Ecological succession]]