soil formation

Soil develops through a series of changes.{{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://fr.1lib.sk/book/832215/8895f4 |access-date=27 May 2025 |archive-url=https://web.archive.org/web/20130225050838/http://soilandhealth.org/01aglibrary/010159.Jenny.pdf |archive-date=25 February 2013 |url-status=live }} The starting point is weathering of freshly accumulated parent material. A variety of soil microbes (bacteria, archaea, 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 organic residues which contribute to humus formation.{{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=27 May 2025 }} Plant roots with their symbiotic mycorrhizal fungi are also able to extract nutrients from rocks.{{cite journal |last1=Augusto |first1=Laurent |last2=Fanin |first2=Nicolas |last3=Bakker |first3=Mark R. |journal=Functional Ecology |volume=33 |issue=5 |title=When plants eat rocks: functional adaptation of roots on rock outcrops |year=2019 |pages=760‒61 |doi=10.1111/1365-2435.13325 |s2cid=164450031 |doi-access=free |bibcode=2019FuEco..33..760A }}

New soils increase in depth by a combination of weathering and further deposition. The soil production rate due to weathering is approximately 1/10 mm per year.{{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://fr.1lib.sk/book/86511583/f88f59 |access-date=27 May 2025 }} New soils can also deepen from 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 plant and animal communities.{{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=27 May 2025 }} Topsoils deepen with the accumulation of humus originating from dead remains of higher plants and soil microbes.{{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=27 May 2025 }} They also deepen through mixing of organic matter with weathered minerals.{{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://fr.1lib.sk/book/95571300/e8b5ea |access-date=27 May 2025 }} As soils mature, they develop soil horizons as organic matter accumulates and mineral weathering and leaching take place.

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.{{cite book |last=Jenny |first=Hans |title=Factors of soil formation: a system of qunatitative pedology |year=1941 |publisher=McGraw-Hill |location=New York, New York |url=https://netedu.xauat.edu.cn/sykc/hjx/content/ckzl/6/2.pdf |access-date=27 May 2025 |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 }} When reordered to climate, organisms, relief, parent material, and time, they form the acronym CLORPT.{{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 Association of American Geographers |volume=95 |issue=1 |pages=11–31 |url=https://fr.1lib.sk/book/41541153/531261 |doi=10.1111/j.1467-8306.2005.00448.x |s2cid=73651791 |access-date=27 May 2025 }}

The mineral material from which a soil forms is called parent material. Rock, whether its origin is igneous, sedimentary, or metamorphic, is the source of all soil mineral materials and the origin of all plant nutrients with the exceptions of nitrogen, hydrogen and carbon. As the parent rock is chemically and physically weathered, transported, deposited and precipitated, it is transformed into a soil.{{cite book |last=Brady |first=Nyle C. |title=The nature and properties of soils |edition=ninth |date=1984 |publisher=Macmillan |location=London, United Kingdom |isbn=978-0029460306 |url=https://fr.1lib.sk/book/12005464/452990 |access-date=27 May 2025 }}

Typical soil parent mineral materials are:{{sfn|Donahue|Miller|Shickluna|1977|pp=20–21}}

• Quartz: SiO₂
• Calcite: CaCO₃
• Feldspar: KAlSi₃O₈
• Mica (biotite): {{chem|K(Mg,Fe)|3|(AlSi|3|O|10|)(F,OH)|2}}

File:Lössacker.jpg 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.{{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=27 May 2025 }}

Residual soils are soils that develop from their underlying parent rocks and have the same general chemistry as those rocks.{{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 |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=27 May 2025 }} The soils found on mesas, plateaux, and plains 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.{{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 |page=113936 |url=https://fr.1lib.sk/book/107867946/ef4640 |doi=10.1016/j.geoderma.2019.113936 |bibcode=2019Geode.35613936S |s2cid=202908885 |access-date=27 May 2025 }}
• Water-transported materials are classed as either alluvial, lacustrine, or marine. Alluvial materials are those moved and deposited by flowing water. Sedimentary deposits settled in lakes are called lacustrine. Lake Bonneville and many soils around the Great Lakes are examples.{{cite book |last=Bockheim |first=James G. |year=2020 |chapter=Soil-forming factors of the Great Lakes coastal zone |title=Soils of the Laurentian Great Lakes, USA and Canada |pages=17–34 |editor-last=Bockheim |editor-first=James G. |publisher=Springer Nature |location=Cham, Switzerland |isbn=978-3-030-52425-8 |chapter-url=https://www.academia.edu/122234142 |doi=

10.1007/978-3-030-52425-8_2 |access-date=27 May 2025 }} Marine deposits, such as soils along the Atlantic and Gulf Coasts and in the Imperial Valley of California are the beds of ancient seas that have been revealed as the land uplifted.{{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://fr.1lib.sk/book/48381708/bee60d |doi=10.1016/0016-7061(91)90073-3 |bibcode=1991Geode..51..241M |access-date=27 May 2025 }}

• Ice moves parent material and makes deposits in the form of terminal and lateral moraines in the case of stationary glaciers. Retreating glaciers leave smoother ground moraines, and in all cases outwash plains are left as alluvial deposits are moved downstream from the glacier.{{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=27 May 2025 }}
• Parent material moved by gravity is obvious at the base of steep slopes as talus cones and is called colluvial material.{{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://fr.1lib.sk/book/102111475/17386e |doi=10.1111/ejss.12673 |bibcode=2018EuJSS..69..577Z |s2cid=102565037 |access-date=27 May 2025 }}

Cumulose parent material is not moved but originates from deposited organic material. This includes peat and 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.{{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=27 May 2025 }}

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.{{cite web |url=http://uregina.ca/~sauchyn/geog323/weather.html |title=Weathering |website=University of Regina |access-date=27 May 2025 }} 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 °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.{{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=1953 |edition=first |publisher=W.H. Freeman |location=San Francisco, California |url=https://fr.1lib.sk/book/115342039/55d1eb |access-date=27 May 2025 }} Structural changes are the result of hydration, oxidation, and reduction. Chemical weathering mainly results from the excretion of organic acids and chelating compounds by bacteria{{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://www.academia.edu/103413378 |access-date=27 May 2025 }} and fungi,{{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=27 May 2025 }} thought to increase under greenhouse effect.{{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 |doi-access=free }}

• 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.{{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 and Hydrogeology |volume=31 |issue=4 |pages=359–67 |url=https://fr.1lib.sk/book/67707312/9e33be |doi=10.1144/GSL.QJEG.1998.031.P4.09 |bibcode=1998QJEGH..31..359H |s2cid=128917530 |access-date=27 May 2025 }} 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}}

1. The 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.{{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=27 May 2025 |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 }}
2. Hydrolysis is the transformation of minerals into 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.{{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://www.academia.edu/88321736 |doi=10.1016/0016-7037(95)00326-6 |bibcode=1995GeCoA..59.5039O |access-date=27 May 2025 }}
3. In carbonation, the solution of carbon dioxide in water forms carbonic acid. Carbonic acid will transform calcite into more soluble calcium bicarbonate.{{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://fr.1lib.sk/book/50985244/ceffd7 |access-date=27 May 2025 }}
4. Hydration is the inclusion of water in a mineral structure, causing it to swell and leaving it stressed and easily decomposed.{{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 }}
5. 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).{{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 |volume=13 |issue=5 |pages=623–26 |url=https://www.researchgate.net/publication/230680185 |doi=10.1088/0957-4484/13/5/316 |access-date=27 May 2025 |bibcode=2002Nanot..13..623M |s2cid=250738729 }}
6. 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 waterlogged conditions.{{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://fr.1lib.sk/book/36692671/e9e215 |access-date=27 May 2025 }}

Of the above, hydrolysis and carbonation are the most effective, in particular in regions of high rainfall, temperature and physical erosion.{{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=https://people.geog.ucsb.edu/~bodo/Geog295-Fall2012/riebe2004_mineral_weathering.pdf |doi=10.1016/j.epsl.2004.05.019 |access-date=27 May 2025 |bibcode=2004E&PSL.224..547R }} Chemical weathering becomes more effective as the surface area of the rock increases, thus is favoured by physical disintegration.{{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 }} This stems in latitudinal and altitudinal climate gradients in regolith formation.{{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://www.academia.edu/96678835 |bibcode=2013GeCoA.122..101D |access-date=27 May 2025 }}{{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://fr.1lib.sk/book/39493370/c3942a |access-date=27 May 2025 }}

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).{{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=https://home.uevora.pt/~lopes/Artigos/23.PDF |doi=10.1016/S0341-8162(02)00017-6 |bibcode=2002Caten..49...41S |access-date=28 May 2025 }}

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.{{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://fr.1lib.sk/book/39393026/474b99 |doi=10.1007/s003740050424 |bibcode=1998BioFS..27..221M |s2cid=44244791 |access-date=28 May 2025 }} 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.{{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 |volume=83 |issue=2 |pages=320–27 |url=https://www.researchgate.net/publication/233379719 |doi=10.2307/2680016 |jstor=2680016 |access-date=28 May 2025 }} 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.{{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=28 May 2025 }}

Climate is the dominant factor in soil formation, and soils show the distinctive characteristics of the climate zones in which they form, with a feedback to climate through transfer of carbon stocked in soil horizons back to the atmosphere.{{cite journal |last1=Davidson |first1=Eric A. |last2=Janssens |first2=Ivan A. |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 |url=https://www.researchgate.net/publication/7253750 |access-date=28 May 2025 }} If warm temperatures and abundant water are present in the profile at the same time, the processes of weathering, leaching, and 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 and semiarid regions, while shrubs and brush of various kinds dominate in arid areas.{{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 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 May 2025 }}

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.{{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=GSA Today |volume=20 |issue=2 |pages=4–9 |doi=10.1130/GSAT57A.1 |url=https://rock.geosociety.org/net/gsatoday/archive/20/2/pdf/i1052-5173-20-2-4.pdf |access-date=28 May 2025 }} 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{{cite journal |last=Fedoroff |first=Nicolas |year=1997 |title=Clay illuviation in Red Mediterranean soils |url=https://fr.1lib.sk/book/50141066/6533fc |journal=Catena |volume=28 |issue=3–4 |pages=171–89 |doi=10.1016/S0341-8162(96)00036-7 |bibcode=1997Caten..28..171F |access-date=28 May 2025 }} and dissolved organic matter.{{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=28 May 2025 }} 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{{cite journal |last=Bernstein |first=Leon |year=1975 |title=Effects of salinity and sodicity on plant growth |url=https://fr.1lib.sk/book/47778554/05405d |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=28 May 2025 }} and microbial growth.{{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://fr.1lib.sk/book/48705974/bd7881 |doi=10.1016/j.apsoil.2006.07.004 |bibcode=2007AppSE..35..319Y |access-date=28 May 2025 }} Soil profiles in arid and semi-arid regions are also apt to accumulate carbonates and certain types of expansive clays (calcrete or caliche horizons).{{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=28 May 2025 }}{{cite journal |last1=Nalbantoglu |first1=Zalihe |last2=Gucbilmez |first2=Emin |year=2001 |title=Improvement of calcareous expansive soils in semi-arid environments |url=https://www.academia.edu/63404175 |journal=Journal of Arid Environments |volume=47 |issue=4 |pages=453–63 |doi=10.1006/jare.2000.0726 |bibcode=2001JArEn..47..453N |access-date=28 May 2025 }} 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 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.{{cite journal |last=Retallack |first=Gregory J. |year=2010 |title=Lateritization and bauxitization events |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=28 May 2025 }}

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{{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 |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=28 May 2025 |bibcode=1987GSLSP..35..139P |s2cid=128746705 }} or far from the entrainment source.{{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 }} 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.{{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://fr.1lib.sk/book/42586803/7faf42 |journal=Nature |volume=298 |issue=5870 |pages=156–59 |doi=10.1038/298156a0 |bibcode=1982Natur.298..156P |s2cid=4311653 |access-date=28 May 2025 }} The effectiveness of water in weathering parent rock material depends on seasonal and daily temperature fluctuations, which favour tensile stresses in rock minerals, and thus their mechanical disaggregation, a process called thermal fatigue.{{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/1209637 |journal=Geomorphology |volume=78 |issue=3/4 |pages=236–49 |doi=10.1016/j.geomorph.2005.12.013 |bibcode=2006Geomo..78..236G |access-date=28 May 2025 }} By the same process freeze-thaw cycles are an effective mechanism which breaks up rocks and other consolidated materials.{{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://fr.1lib.sk/book/31382952/b428e2 |access-date=28 May 2025 }}

The topography, or relief, is characterized by the inclination (slope), elevation, and orientation of the terrain (aspect). Topography determines the rate of precipitation or 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.{{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://fr.1lib.sk/book/48994186/067cc5 |doi=10.1016/j.foreco.2008.08.010 |bibcode=2009ForEM.257....1G |access-date=28 May 2025 }}

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.{{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=28 May 2025 }} 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.{{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=28 May 2025 }}

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.{{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 |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=28 May 2025 }} 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's path will be drier than soils on slopes that do not.{{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://fr.1lib.sk/book/104993342/4d6565 |doi=10.2134/agronj1982.00021962007400060016x |access-date=28 May 2025 }}

In swales and depressions where runoff water tends to concentrate, the regolith is usually more deeply weathered, and soil profile development is more advanced.{{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://fr.1lib.sk/book/55341306/99a940 |doi=10.2136/sssaj1990.03615995005400050027x |bibcode=1990SSASJ..54.1362G |access-date=28 May 2025 }} 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 marshes or peat bogs.{{cite book |last=Brinson |first=Mark M. |title=A hydrogeomorphic classification for wetlands |year=1993 |publisher=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=28 May 2025 }}

Recurring patterns of topography result in toposequences or soil catenas. These patterns emerge from topographic differences in erosion, deposition, fertility, soil moisture, plant cover, soil biology, fire history, and exposure to the elements. Gravity transports water downslope, together with mineral and organic solutes and colloids, increasing particulate and base content at the foot of hills and mountains.{{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://fr.1lib.sk/book/103190344/5ed1ff |doi=10.2134/agronj2004.0252 |bibcode=2004AgrJ...96..252J |access-date=29 May 2025 }} However, many other factors like drainage and erosion interact with slope position, blurring its expected influence on crop yield.{{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=29 May 2025 |bibcode=2010AgrJ..102..513T }}

Each soil has a unique combination of microbial, plant, animal and human influences acting upon it. 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.{{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 |page=13003 |doi=10.1038/s41598-017-12731-7 |pmid=29021579 |pmc=5636888 |bibcode=2017NatSR...713003W |url=https://www.researchgate.net/publication/320333652 |access-date=29 May 2025 }} Plants hold soil against erosion, and accumulated plant material build soil humus levels. Plant root exudation supports microbial activity. Animals serve to decompose plant materials and mix soil through bioturbation.

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.{{cite book |last1=Wall |first1=Diana H. |last2=Adams |first2=Gina |last3=Parsons |first3=Andrew N. |chapter=Soil biodiversity |series=Ecological studies |year=2001 |volume=152 |publisher=Springer |location=New York, New York |doi=10.1007/978-1-4613-0157-8 |isbn=978-0-387-95286-4 |s2cid=45261145 |title=Global biodiversity in a changing environment: scenarios for the 21st century |editor1-last=Chapin |editor1-first=F.Stuart III |editor2-last=Sala |editor2-first=Osvaldo E. |editor3-last=Huber-Sannwald |editor3-first=Elisabeth |url=https://archive.org/details/wall-et-al.-2001 |access-date=29 May 2025 }}{{cite journal |last=Dance |first=Amber |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=29 May 2025 }} There may be a microbial 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.{{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 |volume=309 |issue=5739 |pages=1387–90 |url=https://www.researchgate.net/publication/7637990 |doi=10.1126/science.1112665 |pmid=16123304 |access-date=29 May 2025 |bibcode=2005Sci...309.1387G |s2cid=130269020 }}{{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://www.academia.edu/94942780 |access-date=29 May 2025 }} The number of organisms and species can vary widely according to soil type, location, and depth.

Plants, animals, fungi, bacteria and humans affect soil formation (see soil biomantle and stonelayer). Soil animals, including soil macrofauna (e.g. earthworms, termites, tenebrionids, gophers, moles) and soil mesofauna (e.g. enchytraeids, springtails, mites), mix soils as they form burrows and pores, allowing moisture and gases to move about, a process called bioturbation.{{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=29 May 2025 }} In the same way, plant roots penetrate soil horizons and open channels upon decomposition.{{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=30 May 2025 |bibcode=2004SSASJ..68.1403W }} Plants with deep taproots can penetrate many metres through the different soil layers to bring up nutrients from deeper in the profile.{{cite journal |last=Lynch |first=Jonathan |year=1995 |title=Root architecture and plant productivity |journal=Plant Physiology |url=https://fr.1lib.sk/book/81554637/f65c64 |volume=109 |issue=1 |pages=7–13 |doi=10.1104/pp.109.1.7 |pmid=12228579 |pmc=157559 |access-date=30 May 2025 }} 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.{{cite journal |last=Nguyen |first=Christophe |year=2003 |title=Rhizodeposition of organic C by plants: mechanisms and controls |journal=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=30 May 2025 }}

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.{{cite journal |last1=Bundt |first1=Maya |last2=Widmer |first2=Franco |last3=Pesaro |first3=Manuel |last4=Zeyer |first4=Josef |last5=Blaser |first5=Peter |year=2001 |title=Preferential flow paths: biological 'hot spots' in soils |doi=10.1016/S0038-0717(00)00218-2 |journal=Soil Biology and Biochemistry |volume=33 |issue=6 |pages=729–38 |url=https://www.researchgate.net/publication/223449168 |access-date=30 May 2025 }} The growth of roots through the soil stimulates microbial populations, stimulating in turn the activity of their predators (notably amoeba), thereby increasing the mineralization rate, and in last turn root growth, a positive feedback called the soil microbial loop.{{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 }} Out of root influence, in the bulk soil most bacteria are in a quiescent stage, forming micro-aggregates, i.e. mucilaginous colonies to which clay particles are glued, offering them a protection against desiccation and predation by soil microfauna (bacteriophagous protozoa and nematodes).{{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=30 May 2025 }} Microaggregates (20–250 μm) are ingested by soil fauna, and bacterial bodies are partly or totally digested in their guts.{{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=30 May 2025 }}

Humans impact soil formation by removing vegetation cover through tillage, application of herbicides, fire and leaving soils bare. This can lead to erosion, waterlogging, lateritization or podzolization (according to climate and topography).{{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=30 May 2025 }} 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.{{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://fr.1lib.sk/book/55340885/0cdf28 |doi=10.2136/sssaj1989.03615995005300020047x |bibcode=1989SSASJ..53..582K |access-date=30 May 2025 }}

Earthworms, ants, termites, moles, gophers, as well as some millipedes and tenebrionid beetles, mix the soil as they burrow, significantly affecting soil formation.{{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://www.academia.edu/102507924 |access-date=30 May 2025 }} Earthworms ingest soil particles and organic residues, enhancing the availability of plant nutrients in the material that passes through their bodies.{{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://fr.1lib.sk/book/50527858/85ce85 |access-date=30 May 2025 }} 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,{{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://fr.1lib.sk/book/37642844/b0379a |access-date=30 May 2025 }} thereby assuring ready infiltration of water.{{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://fr.1lib.sk/book/49827228/4e5c48 |access-date=30 May 2025 }} As ants and termites build mounds, earthworms transport soil materials from one horizon to another.{{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 May 2025 }} 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,{{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 May 2025 }} exert a priming effect on soil microflora,{{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://fr.1lib.sk/book/38617204/914053 |access-date=30 May 2025 }} giving them the status of ecosystem engineers, which they share with ants and termites.{{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 May 2025 }}

In general, the mixing of the soil by the activities of animals, sometimes called pedoturbation, tends to undo or counteract the tendency of other soil-forming processes that create distinct horizons.{{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 May 2025 |jstor=3868431 }} 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,{{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 May 2025 }} the same for the deposition of casts at the soil surface by earthworms.{{cite journal |last1=Le Bayon |first1=Renée-Claire |last2=Binet |first2=Françoise |year=2001 |title=Earthworm surface casts affect soil erosion by runoff water and phosphorus transfer in a temperate maize crop |journal=Pedobiologia |volume=45 |issue=5 |pages=430–42 |url=https://www.researchgate.net/publication/248907085 |doi=10.1078/0031-4056-00097 |access-date=30 May 2025 }} Large animals such as gophers, moles, and prairie dogs bore into the lower soil horizons, bringing materials to the surface.{{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 May 2025 }} 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 or krotovinas.{{cite journal |last1=Zhang |first1=Aimin |last2=Long |first2=Hao |last3=Yang |first3=Fei |last4=Zhang |first4=Jingran |last5=Peng |first5=Jun |last6=Gong |first6=Keyang |last7=Hong |first7=Yunpeng |last8=Shi |first8=Yonghui |last9=Zhou |first9=Shengfang |last10=Shao |first10=Zhudong |last11=Yang |first11=Na |last12=Huang |first12=Xiaoling |last13=Huang |first13=Xiaoling |last14=Luo |first14=Xi |last15=Zhang |first15=Ganlin |journal=Catena |title=Revisiting krotovina formation using luminescence dating: a case study from NE China |year=2025 |volume=248 |page=108554 |doi=10.1016/j.catena.2024.108554 |url=https://www.researchgate.net/publication/386505967 |access-date=30 May 2025 }}

Vegetation impacts soils in numerous ways. It can prevent erosion caused by excessive rain that might result from surface runoff.{{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://fr.1lib.sk/book/55546991/c4a302 |doi=10.1191/0309133305pp443ra |bibcode=2005PrPG...29..189G |s2cid=55243167 |access-date=30 May 2025 }} Plants shade soils, keeping them cooler{{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 }} and slowing evaporation of soil moisture.{{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://fr.1lib.sk/book/57283986/483301 |access-date=30 May 2025 }} 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.{{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://fr.1lib.sk/book/46599036/da840f |doi=10.1016/S1464-1909(99)00052-0 |bibcode=1999PCEB...24..609H |access-date=30 May 2025 }} Plants can form new chemicals that can break down minerals, both directly{{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://fr.1lib.sk/book/43162129/2e43ea |doi=10.1023/A:1004356007312 |bibcode=1998PlSoi.205...25J |s2cid=26813067 |access-date=30 May 2025 }} and indirectly through mycorrhizal fungi and rhizosphere bacteria,{{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 |url=https://www.researchgate.net/publication/7312017 |access-date=30 May 2025 }} and improve the soil structure.{{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=30 May 2025 }} The type and amount of vegetation depend on climate, topography, soil characteristics and biological factors, mediated or not by human activities.{{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=30 May 2025 |bibcode=2011JArL....3...25S }}{{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://fr.1lib.sk/book/36804776/43c093 |access-date=30 May 2025 |bibcode=2003GloEB..12..131V }} 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.{{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 }}

The influence of humans, and by association, fire, are state factors placed within the organisms state factor.{{cite journal |url=https://fr.1lib.sk/book/90067118/df8e3f |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=2 June 2025 }} Humans can import or extract nutrients and energy in ways that dramatically change soil formation. Accelerated soil erosion from overgrazing, and Pre-Columbian terraforming in the Amazon basin resulting in terra preta are two examples of the effects of human management.{{cite journal |last=Evans |first=Robert |year=1977 |title=Overgrazing and soil erosion on hill pastures with particular reference to the Peak District |url=https://fr.1lib.sk/book/41196548/e87c7d |journal=Grass and Forage Science |volume=32 |issue=2 |pages=65–76 |doi=10.1111/j.1365-2494.1977.tb01415.x |access-date=2 June 2025 }}{{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.academia.edu/45092595 |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=2 June 2025 }}

It is believed that Native Americans regularly set fires to maintain several large areas of prairie grasslands in Indiana and Michigan, although climate and mammalian grazers (e.g. bisons) are also advocated to explain the maintenance of the Great Plains of North America.{{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 |doi-access=free }} In more recent times, human destruction of natural vegetation and subsequent tillage of the soil for crop production has abruptly modified soil formation.{{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=2 June 2025 |bibcode=1989SSASJ..53..800B }} Likewise, irrigating soil in an arid region drastically influences soil-forming factors,{{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=https://www.researchgate.net/publication/303355634 |doi=10.3103/S1068367416020075 |bibcode=2016RuAgS..42..155L |s2cid=43356998 |access-date=2 June 2025 }} as does adding fertilizer and lime to soils of low fertility.{{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=2 June 2025 }}

Distinct ecosystems produce distinct soils, sometimes in easily observable ways. For example, three species of land snails in the genus Euchondrus in the Negev desert are noted for eating lichens 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.{{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.1lib.sk/book/110223859/aef56c |doi=10.1515/9781400847266 |access-date=2 June 2025 }} 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.

The effects of ancient ecosystems are not as easily observed, and this challenges the understanding of soil formation. For example, the chernozems 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 fires capable of producing these distinct deep rich black soils are not easily observed.{{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=285–97 |url=https://cdnsciencepub.com/doi/pdf/10.4141/S00-075 |doi=10.4141/S00-075 |bibcode=2001CaJSS..81..285P |access-date=2 June 2025 }} It is now accepted that Neolithic human-caused wildfires enriched soils in charcoal (also called black carbon) and played a prominent role in the formation of the fertile chernozems and terra preta, actively used for the sake of agricuture.{{cite journal |last1=Holmer |first1=Anna S. |last2=Bösze |first2=Ildikó |last3=Mossbauer |first3=Günther |last4=Lindauer |first4=Susanne |last5=Völkel |first5=Jörg |title=Neolithic formation of chernozem in south-eastern Germany? |year=2025 |journal=Catena |volume=248 |page=108543 |url=https://www.researchgate.net/publication/386044440 |doi=10.1016/j.catena.2024.108543 |access-date=2 June 2025 }}{{cite journal |last1=Rodrigues |first1=Aline Furtado |last2=Novotny |first2=Etelvino Henrique |last3=Knicker |first3=Heike |last4=de Oliveira |first4=Rogério Ribeiro |title=Humic acid composition and soil fertility of soils near an ancient charcoal kiln: are they similar to Terra Preta de Índios soils? |year=2019 |journal=Journal of Soils and Sediments |volume=19 |pages=1374–81 |url=https://www.researchgate.net/publication/328345136 |doi=10.1007/s11368-018-2162-5 |access-date=2 June 2025 }}

Time is a factor in the interactions of all the above. While a mixture of sand, silt and clay constitute the texture of a soil and the aggregation of those components produces peds, the development of a distinct B horizon marks the development of a soil or pedogenesis.{{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=https://www.fsl.orst.edu/ltep/Reprints_files/Bormann%20JE1995%20windthrow%20chrono.pdf |access-date=2 June 2025 |doi=10.2307/2261411 |jstor=2261411 |bibcode=1995JEcol..83..747B |s2cid=85818050 }} With time, soils will evolve features that depend on the interplay of the prior listed soil-forming factors. It takes decades{{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.1lib.sk/book/78321353/7d4e4f |doi=10.2307/2257005 |access-date=2 June 2025 |jstor=2257005 |bibcode=1955JEcol..43..427C }} to several thousand years for a soil to develop a profile,{{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 |volume=76 |issue=5 |pages=1407–24 |url=https://www.researchgate.net/publication/259671947 |doi=10.2307/1938144 |access-date=2 June 2025 |jstor=1938144 }} 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.{{cite journal |last=Huggett |first=Richard J. |year=1998 |title=Soil chronosequences, soil development, and soil evolution: a critical review |journal=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=2 June 2025 }} 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.{{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.1lib.sk/book/36845957/c50521 |doi=10.1046/j.1526-100X.2002.01020.x |bibcode=2002ResEc..10..248C |s2cid=55198244 |access-date=2 June 2025 }} 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, the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion.{{cite book |last1=Shipitalo |first1=Martin J. |last2=Le Bayon |first2=Renée-Claire |year=2004 |chapter=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 |chapter-url=https://www.researchgate.net/publication/41844767 |access-date=2 June 2025 }} Despite the inevitability of soil retrogression and degradation, most soil cycles are long.

Soil-forming factors continue to affect soils during their existence, even on stable landscapes that are long-enduring, some for millions of years. Materials are deposited on top{{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=Geografisk Tidsskrift |volume=107 |issue=1 |pages=9–15 |doi=10.1080/00167223.2007.10801371 |bibcode=2007GeTid.107....9H |s2cid=128479624 |url=https://www.researchgate.net/publication/258240253 |access-date=2 June 2025 }} or are blown or washed from the surface.{{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 |volume=267 |issue=5201 |pages=1117–23 |url=https://www.academia.edu/9512072 |doi=10.1126/science.267.5201.1117 |access-date=2 June 2025 |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 }} 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.{{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=2 June 2025 |bibcode=1992Geode..52..251W }}

Time as a soil-forming factor may be investigated by studying soil chronosequences, in which soils of different ages but with minor differences in other soil-forming factors can be compared. Paleosols are soils formed during previous soil forming conditions.

File:Soil-formation-factors-en.jpg

Russian geologist Vasily Dokuchaev, commonly regarded as the father of pedology, determined in 1883{{cite book |last=Dokuchaev |first=Vasily V. |title=Russian Chernozem |url=https://viewer.rsl.ru/ru/rsl01004897898?page=249 }} 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:{{cite book |author-last=Jenny |author-first=Hans |author-link=Hans Jenny (pedologist) |url=https://archive.org/details/soilresourceorig0000jenn |year=1980 |title=The soil resource: origin and behavior |series=Ecological studies |volume=37 |publisher=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_r |access-date=2 June 2025 }}

: {{math| soil {{=}} f(cl, o, p) t_r}}

(where cl or c {{=}} climate, o {{=}} biological processes, p {{=}} parent material) t_r {{=}} relative time (young, mature, old)

American soil scientist Hans Jenny published in 1941{{cite book |last=Jenny |first=Hans |title=Factors of soil formation: a system of quantitative pedology |edition=First |date=1941 |publisher=McGraw-Hill |location=New York, New York |isbn=978-0486681283 |url=https://soilandhealth.org/wp-content/uploads/01aglibrary/010159.Jenny.pdf |access-date=2 June 2025 }} a state equation for the factors influencing soil formation:

: {{math| S {{=}} f(cl, o, r, p, t, ...) }}

• S soil formation
• cl (sometimes c) climate
• o organisms (soil microbiology, soil mesofauna, soil biology)
• r relief
• p parent material
• t 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 surveyors all over the world as a qualitative list for understanding the factors that may be important for producing the soil pattern within a region.{{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 Association of American Geographers |volume=95 |pages=11–31 |doi=10.1111/j.1467-8306.2005.00448.x |s2cid=73651791 |url=https://fr.1lib.sk/book/41541153/531261 |access-date=2 June 2025 }}

An example of the evolution of soils in prehistoric lake beds is in the Makgadikgadi Pans of the Kalahari Desert, where a change in an ancient river course led to millennia of salinity buildup and formation of calcretes and silcretes.{{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=2 June 2025 }}

{{Reflist}}

{{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

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Category:Pedology

Category:Ecological succession