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[[File:Estructura-suelo.jpg|thumb|right|alt= This is a diagram and related photograph of soil layers from bedrock to soil.|A, B, and C represent the [[soil horizon|soil profile]], a notation firstly coined by [[Vasily Dokuchaev]] (1846–1903), the father of [[pedology]] |
[[File:Estructura-suelo.jpg|thumb|right|alt= This is a diagram and related photograph of soil layers from bedrock to soil.|A, B, and C represent the [[soil horizon|soil profile]], a notation firstly coined by [[Vasily Dokuchaev]] (1846–1903), the father of [[pedology]]. Here, A is the [[topsoil]]; B is a [[regolith]]; C is a [[saprolite]] (a less-weathered regolith); the bottom-most layer represents the [[bedrock]].]] |
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[[File:Stagnogley.JPG|thumb|Surface-water-[[Gley soil|gley]] developed in [[glacial till]] |
[[File:Stagnogley.JPG|thumb|Surface-water-[[Gley soil|gley]] developed in [[glacial till]] in [[Northern Ireland]]]] |
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'''Soil''' is a [[mixture]] of [[organic matter]], [[minerals]], [[gas]]es, [[liquid]]s, and [[organism]]s that together support [[life]]. [[ |
'''Soil''', also commonly referred to as '''earth''' or '''[[dirt]]''', is a [[mixture]] of [[organic matter]], [[minerals]], [[gas]]es, [[liquid]]s, and [[organism]]s that together support [[life]]. (Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former term specifically to displaced soil.) The term ''[[:wikt:pedolith|pedolith]]'', used commonly to refer to the soil, translates to ''ground stone'' in the sense ''fundamental stone'', from the ancient Greek word {{Lang|grc|πέδον}}, meaning 'ground, earth'. |
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Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a [[Porosity|porous]] phase that holds [[Soil gas|gases]] (the soil atmosphere) and [[water]] (the soil solution).<ref>{{cite book |last1=Voroney |first1=R. Paul |title=Soil microbiology, ecology and biochemistry |last2=Heck |first2=Richard J. |date=2007 |publisher=[[Elsevier]] |isbn=978-0-12-546807-7 |editor-last=Paul |editor-first=Eldor A. |edition=3rd |location=Amsterdam, the Netherlands |pages=25–49 |chapter=The soil habitat |doi=10.1016/B978-0-08-047514-1.50006-8 |access-date=27 March 2022 |chapter-url=https://fr.art1lib.org/book/34240339/73458e |archive-url=https://web.archive.org/web/20180710102532/http://csmi.issas.ac.cn/uploadfiles/Soil%20Microbiology%2C%20Ecology%20%26%20Biochemistry.pdf |archive-date=10 July 2018 |url-status=live |df=dmy-all}}</ref><ref>{{cite book |last1=Taylor |first1=Sterling A. |url=https://archive.org/details/physicaledapholo0000tayl |title=Physical edaphology: the physics of irrigated and nonirrigated soils |last2=Ashcroft |first2=Gaylen L. |date=1972 |publisher=[[W. H. Freeman and Company|W.H. Freeman]] |isbn=978-0-7167-0818-6 |location=San Francisco, California |url-access=registration}}</ref> Accordingly, soil is a three-[[state of matter|state]] system of solids, liquids, and gases.<ref>{{cite book |last=McCarthy |first=David F. |url=https://fr.book4you.org/book/3555343/0f8f97 |title=Essentials of soil mechanics and foundations: basic geotechnics |date=2014 |publisher=[[Pearson Education|Pearson]] |isbn=9781292039398 |edition=7th |location=London, United Kingdom |access-date=27 March 2022}}</ref> Soil is a product of several factors: the influence of [[climate]], [[terrain|relief]] (elevation, orientation, and slope of terrain), organisms, and the soil's [[parent material]]s (original minerals) interacting over time.<ref name="Gilluly1975">{{cite book |last1=Gilluly |first1=James |url=https://archive.org/details/principlesofgeol0000gill |title=Principles of geology |last2=Waters |first2=Aaron Clement |last3=Woodford |first3=Alfred Oswald |date=1975 |publisher=[[W. H. Freeman and Company|W.H. Freeman]] |isbn=978-0-7167-0269-6 |edition=4th |location=San Francisco, California |author-link1=James Gilluly |url-access=registration}}</ref> It continually undergoes development by way of numerous physical, chemical and biological processes, which include [[weathering]] with associated [[erosion]]. Given its complexity and strong internal [[connectedness]], [[Soil ecology|soil ecologists]] regard soil as an [[ecosystem]].<ref>{{cite journal |last=Ponge |first=Jean-François |year=2015 |title=The soil as an ecosystem |url=https://www.researchgate.net/publication/276090499 |journal=Biology and Fertility of Soils |volume=51 |issue=6 |pages=645–648 |doi=10.1007/s00374-015-1016-1 |access-date=3 April 2022 |s2cid=18251180}}</ref> |
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⚫ | Most soils have a dry [[bulk density]] (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm<sup>3</sup>, though the soil [[Particle density (packed density)|particle density]] is much higher, in the range of 2.6 to 2.7 g/cm<sup>3</sup>.<ref name="Yu2015">{{cite web |last1=Yu |first1=Charley |last2=Kamboj |first2=Sunita |last3=Wang |first3=Cheng |last4=Cheng |first4=Jing-Jy |year=2015 |title=Data collection handbook to support modeling impacts of radioactive material in soil and building structures |url=https://resrad.evs.anl.gov/docs/data_collection.pdf |url-status=live |archive-url=https://web.archive.org/web/20180804105951/http://resrad.evs.anl.gov/docs/data_collection.pdf |archive-date=4 August 2018 |access-date=3 April 2022 |website=[[Argonne National Laboratory]] |pages=13–21}}</ref> Little of the soil of [[planet Earth]] is older than the [[Pleistocene]] and none is older than the [[Cenozoic]],<ref name="Buol">{{cite book |last1=Buol |first1=Stanley W. |url=https://fr1lib.org/book/2156097/707d35 |title=Soil genesis and classification |last2=Southard |first2=Randal J. |last3=Graham |first3=Robert C. |last4=McDaniel |first4=Paul A. |date=2011 |publisher=[[Wiley-Blackwell]] |isbn=978-0-470-96060-8 |edition=6th |location=Ames, Iowa |access-date=3 April 2022}}</ref> although [[Paleopedological record|fossilized soils]] are preserved from as far back as the [[Archean]].<ref>{{cite journal |last1=Retallack |first1=Gregory J. |last2=Krinsley |first2=David H. |last3=Fischer |first3=Robert |last4=Razink |first4=Joshua J. |last5=Langworthy |first5=Kurt A. |year=2016 |title=Archean coastal-plain paleosols and life on land |url=https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/d/3735/files/2013/07/Retallack-et-al.-2016-Farrel-1gt7uft.pdf |url-status=live |journal=[[Gondwana Research]] |volume=40 |pages=1–20 |bibcode=2016GondR..40....1R |doi=10.1016/j.gr.2016.08.003 |archive-url=https://web.archive.org/web/20181113075710/https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/d/3735/files/2013/07/Retallack-et-al.-2016-Farrel-1gt7uft.pdf |archive-date=13 November 2018 |access-date=3 April 2022 |doi-access=free}}</ref> |
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The pedosphere interfaces with the [[lithosphere]], the [[hydrosphere]], the [[atmosphere]], and the [[biosphere]].<ref name="ches">{{cite book |url=https://fr1lib.org/book/563235/8e916e |title=Encyclopedia of soil science |date=2008 |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-1-4020-3994-2 |editor-last=Chesworth |editor-first=Ward |edition=1st |location=Dordrecht, The Netherlands |access-date=27 March 2022 |archive-url=https://web.archive.org/web/20180905002957/http://www.encyclopedias.biz/dw/Encyclopedia%20of%20Soil%20Science.pdf |archive-date=5 September 2018 |url-status=live}}</ref> Collectively, Earth's body of soil, called the [[pedosphere]], has four important [[soil functions|functions]]: |
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* as a medium for plant growth |
* as a medium for plant growth |
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All of these functions, in their turn, modify the soil and its properties. |
All of these functions, in their turn, modify the soil and its properties. |
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Soil is also commonly referred to as '''earth''' or '''[[dirt]]'''; some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former term specifically to displaced soil. |
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The pedosphere interfaces with the [[lithosphere]], the [[hydrosphere]], the [[atmosphere]], and the [[biosphere]].<ref name="ches">{{cite book |editor-last=Chesworth |editor-first=Ward |date=2008 |title=Encyclopedia of soil science |isbn=978-1-4020-3994-2 |publisher=[[Springer Science+Business Media|Springer]] |location=Dordrecht, The Netherlands |edition=1st |url=https://fr1lib.org/book/563235/8e916e |archive-url=https://web.archive.org/web/20180905002957/http://www.encyclopedias.biz/dw/Encyclopedia%20of%20Soil%20Science.pdf |archive-date=5 September 2018 |url-status=live |access-date=27 March 2022 }}</ref> The term ''[[:wikt:pedolith|pedolith]]'', used commonly to refer to the soil, translates to ''ground stone'' in the sense ''fundamental stone'', from the ancient Greek {{Lang|grc|πέδον}} 'ground, earth'. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a [[Porosity|porous]] phase that holds [[Soil gas|gases]] (the soil atmosphere) and water (the soil solution).<ref>{{cite book |last1=Voroney |first1=R. Paul |last2=Heck |first2=Richard J. |date=2007 |chapter=The soil habitat |doi=10.1016/B978-0-08-047514-1.50006-8 |title=Soil microbiology, ecology and biochemistry |edition=3rd |editor-first=Eldor A. |editor-last=Paul |publisher=[[Elsevier]] |location= Amsterdam, the Netherlands |pages=25–49 |isbn=978-0-12-546807-7 |chapter-url=https://fr.art1lib.org/book/34240339/73458e |archive-url=https://web.archive.org/web/20180710102532/http://csmi.issas.ac.cn/uploadfiles/Soil%20Microbiology%2C%20Ecology%20%26%20Biochemistry.pdf |archive-date=10 July 2018 |url-status=live |df=dmy-all |access-date=27 March 2022 }}</ref><ref>{{cite book |last1=Taylor |first1=Sterling A. |last2=Ashcroft |first2=Gaylen L. |date=1972 |title=Physical edaphology: the physics of irrigated and nonirrigated soils |publisher=[[W. H. Freeman and Company|W.H. Freeman]] |location=San Francisco, California |isbn=978-0-7167-0818-6 |url-access=registration |url=https://archive.org/details/physicaledapholo0000tayl }}</ref> Accordingly, soil scientists can envisage soils as a three-[[state of matter|state]] system of solids, liquids, and gases.<ref>{{cite book |last=McCarthy |first=David F. |date=2014 |title=Essentials of soil mechanics and foundations: basic geotechnics |edition=7th |publisher=[[Pearson Education|Pearson]] |location=London, United Kingdom |url=https://fr.book4you.org/book/3555343/0f8f97 |access-date=27 March 2022 |isbn=9781292039398 }}</ref> |
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Soil is a product of several factors: the influence of [[climate]], [[terrain|relief]] (elevation, orientation, and slope of terrain), organisms, and the soil's [[parent material]]s (original minerals) interacting over time.<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 and Company|W.H. Freeman]] |location=San Francisco, California |isbn=978-0-7167-0269-6 |url-access=registration |url=https://archive.org/details/principlesofgeol0000gill }}</ref> It continually undergoes development by way of numerous physical, chemical and biological processes, which include [[weathering]] with associated [[erosion]]. Given its complexity and strong internal [[connectedness]], [[Soil ecology|soil ecologists]] regard soil as an [[ecosystem]].<ref>{{cite journal |last=Ponge |first=Jean-François |journal=Biology and Fertility of Soils |title=The soil as an ecosystem |year=2015 |volume=51 |issue=6 |pages=645–648 |doi=10.1007/s00374-015-1016-1 |s2cid=18251180 |url=https://www.researchgate.net/publication/276090499 |access-date=3 April 2022 }}</ref> |
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⚫ | Most soils have a dry [[bulk density]] (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm<sup>3</sup>, |
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[[Soil science]] has two basic branches of study: [[edaphology]] and pedology. ''Edaphology'' studies the influence of soils on living things.<ref>{{cite web |url=https://sis.agr.gc.ca/cansis/glossary/e/index.html |title=Glossary of terms in soil science |website=[[Agriculture and Agri-Food Canada]] |date=13 December 2013 |archive-url=https://web.archive.org/web/20181027045042/http://sis.agr.gc.ca/cansis/glossary/e/index.html |archive-date=27 October 2018 |url-status=live |access-date=3 April 2022 }}</ref> ''Pedology'' focuses on the formation, description (morphology), and classification of soils in their natural environment.<ref>{{cite web |url=https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.552.237&rep=rep1&type=pdf |title=Soil preservation and the future of pedology |first=Ronald |last=Amundson |archive-url=https://web.archive.org/web/20180612140029/http://natres.psu.ac.th/Link/SoilCongress/bdd/symp45/75-t.pdf |archive-date=12 June 2018 |url-status=live |access-date=3 April 2022 }}</ref> In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the [[Moon]] and on other [[Astronomical object|celestial objects]].<ref>{{cite web |url=https://www.mps.mpg.de/phd/planetary-interiors-and-surfaces-2011-part-05 |title=Impacts and formation of regolith |last1=Küppers |first1=Michael |last2=Vincent |first2=Jean-Baptiste |website=[[Max Planck Institute for Solar System Research]] |archive-url=https://web.archive.org/web/20180804200824/https://www.mps.mpg.de/phd/planetary-interiors-and-surfaces-2011-part-05 |archive-date=4 August 2018 |url-status=live |access-date=3 April 2022 }}</ref> |
[[Soil science]] has two basic branches of study: [[edaphology]] and pedology. ''Edaphology'' studies the influence of soils on living things.<ref>{{cite web |url=https://sis.agr.gc.ca/cansis/glossary/e/index.html |title=Glossary of terms in soil science |website=[[Agriculture and Agri-Food Canada]] |date=13 December 2013 |archive-url=https://web.archive.org/web/20181027045042/http://sis.agr.gc.ca/cansis/glossary/e/index.html |archive-date=27 October 2018 |url-status=live |access-date=3 April 2022 }}</ref> ''Pedology'' focuses on the formation, description (morphology), and classification of soils in their natural environment.<ref>{{cite web |url=https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.552.237&rep=rep1&type=pdf |title=Soil preservation and the future of pedology |first=Ronald |last=Amundson |archive-url=https://web.archive.org/web/20180612140029/http://natres.psu.ac.th/Link/SoilCongress/bdd/symp45/75-t.pdf |archive-date=12 June 2018 |url-status=live |access-date=3 April 2022 }}</ref> In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the [[Moon]] and on other [[Astronomical object|celestial objects]].<ref>{{cite web |url=https://www.mps.mpg.de/phd/planetary-interiors-and-surfaces-2011-part-05 |title=Impacts and formation of regolith |last1=Küppers |first1=Michael |last2=Vincent |first2=Jean-Baptiste |website=[[Max Planck Institute for Solar System Research]] |archive-url=https://web.archive.org/web/20180804200824/https://www.mps.mpg.de/phd/planetary-interiors-and-surfaces-2011-part-05 |archive-date=4 August 2018 |url-status=live |access-date=3 April 2022 }}</ref> |
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==Processes== |
==Processes== |
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Soil |
Soil is a major component of the [[Earth]]'s [[ecosystem]]. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, with effects ranging from [[ozone depletion]] and [[global warming]] to [[rainforest destruction]] and [[water pollution]]. With respect to Earth's [[carbon cycle]], soil acts as an important [[carbon sink|carbon reservoir]],<ref>{{Cite journal |last1=Amelung |first1=Wulf |last2=Bossio |first2=Deborah |last3=De Vries |first3=Wim |last4=Kögel-Knabner |first4=Ingrid |last5=Lehmann |first5=Johannes |last6=Amundson |first6=Ronald |last7=Bol |first7=Roland |last8=Collins |first8=Chris |last9=Lal |first9=Rattan |last10=Leifeld |first10=Jens |last11=Minasny |first11=Buniman |last12=Pan |first12=Gen-Xing |last13=Paustian |first13=Keith |last14=Rumpel |first14=Cornelia |last15=Sanderman |first15=Jonathan |last16=Van Groeningen |first16=Jan Willem |last17=Mooney |first17=Siân |last18=Van Wesemael |first18=Bas |last19=Wander |first19=Michelle |last20=Chabbi |first20=Abad |date=27 October 2020 |title=Towards a global-scale soil climate mitigation strategy |journal=[[Nature Communications]] |language=en |volume=11 |issue=1 |pages=5427 |doi=10.1038/s41467-020-18887-7 |pmid=33110065 |pmc=7591914 |bibcode=2020NatCo..11.5427A |issn=2041-1723 |url=https://www.nature.com/articles/s41467-020-18887-7.pdf |access-date=3 April 2022 |doi-access=free }}</ref> and it is potentially one of the most reactive to human disturbance<ref>{{cite journal |last1=Pouyat |first1=Richard |last2=Groffman |first2=Peter |last3=Yesilonis |first3=Ian |last4= Hernandez |first4=Luis |journal=[[Environmental Pollution (journal)|Environmental Pollution]] |volume=116 |issue=Supplement 1 |title=Soil carbon pools and fluxes in urban ecosystems |url=https://www.researchgate.net/publication/11526697 |year=2002 |pages=S107–S118 |doi=10.1016/S0269-7491(01)00263-9 |pmid=11833898 |access-date=3 April 2022 |quote=Our analysis of pedon data from several disturbed soil profiles suggests that physical disturbances and anthropogenic inputs of various materials (direct effects) can greatly alter the amount of C stored in these human "made" soils.}}</ref> and climate change.<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=9 March 2006 |pages=165‒73 |url=https://www.nature.com/articles/nature04514.pdf |doi=10.1038/nature04514 |pmid=16525463 |bibcode=2006Natur.440..165D |s2cid=4404915 |access-date=3 April 2022 |doi-access=free }}</ref> As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased [[Soil biology|biological]] activity at higher temperatures, a [[positive feedback]] (amplification).<ref>{{cite journal |last=Powlson |first=David |journal=[[Nature (journal)|Nature]] |volume=433 |title=Will soil amplify climate change? |year=2005 |issue=20 January 2005 |pages=204‒05 |url=https://fr.art1lib.org/book/10543301/528a68 |doi=10.1038/433204a |pmid=15662396 |bibcode=2005Natur.433..204P |s2cid=35007042 |access-date=3 April 2022 }}</ref> This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover.<ref>{{cite journal |last1=Bradford |first1=Mark A. |last2=Wieder |first2=William R. |last3=Bonan |first3=Gordon B. |last4=Fierer |first4=Noah |last5=Raymond |first5=Peter A. |last6=Crowther |first6=Thomas W. |journal=[[Nature Climate Change]] |volume=6 |title=Managing uncertainty in soil carbon feedbacks to climate change |url=http://fiererlab.org/wp-content/uploads/2014/09/Bradford_etal_2016_NCC.pdf |year=2016 |issue=27 July 2016 |pages=751–758 |doi=10.1038/nclimate3071 |access-date=3 April 2022 |bibcode=2016NatCC...6..751B |hdl=20.500.11755/c1792dbf-ce96-4dc7-8851-1ca50a35e5e0 |hdl-access=free }}</ref> |
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Soil acts as an engineering medium, a habitat for [[soil organisms]], a recycling system for [[nutrients]] and [[organic waste]]s, a regulator of [[water quality]], a modifier of [[Atmospheric chemistry|atmospheric composition]], and a medium for [[plant growth]], making it a critically important provider of [[ecosystem services]].<ref>{{cite journal |last1=Dominati |first1=Estelle |last2=Patterson |first2=Murray |last3=Mackay |first3=Alec |journal=[[Ecological Economics (journal)|Ecological Economics]] |volume=69 |issue=9 |title=A framework for classifying and quantifying the natural capital and ecosystem services of soils |year=2010 |url=https://www.researchgate.net/publication/223852147 |pages=1858‒68 |doi=10.1016/j.ecolecon.2010.05.002 |access-date=10 April 2022 |archive-url=https://web.archive.org/web/20170808082847/http://esanalysis.colmex.mx/Sorted%20Papers/2010/2010%20NZL%20-3F%20Phys.pdf |archive-date=8 August 2017 |url-status=live }}</ref> Since soil has a tremendous range of available [[Ecological niche|niches]] and [[habitat]]s, it contains a prominent part of the Earth's [[genetic diversity]]. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored.<ref>{{cite journal |last=Dykhuizen |first=Daniel E. |journal=Antonie van Leeuwenhoek |volume=73 |issue=1 |title=Santa Rosalia revisited: why are there so many species of bacteria? |year=1998 |url=https://www.researchgate.net/publication/13682480 |pages=25‒33 |doi=10.1023/A:1000665216662 |pmid=9602276 |s2cid=17779069 |access-date=10 April 2022 }}</ref><ref>{{cite journal |last1=Torsvik |first1=Vigdis |last2=Øvreås |first2=Lise |journal=[[Current Opinion in Microbiology]] |volume=5 |issue=3 |title=Microbial diversity and function in soil: from genes to ecosystems |year=2002 |pages=240‒45 |url=https://www.academia.edu/13038690 |doi=10.1016/S1369-5274(02)00324-7 |pmid=12057676 |access-date=10 April 2022 }}</ref> Soil has a [[mean]] [[Prokaryote|prokaryotic]] density of roughly 10<sup>8</sup> organisms per gram,<ref>{{cite journal |last1=Raynaud |first1=Xavier |last2=Nunan |first2=Naoise |journal=[[PLOS ONE]] |volume=9 |issue=1 |title=Spatial ecology of bacteria at the microscale in soil |year=2014 |page=e87217 |doi=10.1371/journal.pone.0087217 |pmid=24489873 |pmc=3905020 |bibcode=2014PLoSO...987217R |doi-access=free }}</ref> whereas the ocean has no more than 10<sup>7</sup> prokaryotic organisms per milliliter (gram) of seawater.<ref>{{cite journal |last1=Whitman |first1=William B. |last2=Coleman |first2=David C. |last3=Wiebe |first3=William J. |journal=[[Proceedings of the National Academy of Sciences of the USA]] |volume=95 |issue=12 |title=Prokaryotes: the unseen majority |year=1998 |pages=6578‒83 |doi=10.1073/pnas.95.12.6578 |pmid=9618454 |pmc=33863 |bibcode=1998PNAS...95.6578W |doi-access=free }}</ref> [[Soil organic matter|Organic carbon]] held in soil is eventually returned to the atmosphere through the process of [[cellular respiration|respiration]] carried out by [[heterotrophic]] organisms, but a substantial part is retained in the soil in the form of soil organic matter; [[tillage]] usually increases the rate of [[soil respiration]], leading to the depletion of soil organic matter.<ref>{{cite journal |last1=Schlesinger |first1=William H. |last2=Andrews |first2=Jeffrey A. |journal=Biogeochemistry |volume=48 |issue=1 |title=Soil respiration and the global carbon cycle |year=2000 |url=https://www.researchgate.net/publication/51997678 |pages=7‒20 |doi=10.1023/A:1006247623877 |s2cid=94252768 |access-date=10 April 2022 }}</ref> Since plant roots need oxygen, [[aeration]] is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected [[Pore space in soil|soil pores]], which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the [[Soil water (retention)|water-holding capacity]] of soils is vital for plant survival.<ref>{{cite journal |last1=Denmead |first1=Owen Thomas |last2=Shaw |first2=Robert Harold |journal=[[Agronomy Journal]] |volume=54 |issue=5 |title=Availability of soil water to plants as affected by soil moisture content and meteorological conditions |year=1962 |url=https://www.researchgate.net/publication/250098028 |pages=385‒90 |doi=10.2134/agronj1962.00021962005400050005x |access-date=10 April 2022 }}</ref> |
Soil acts as an engineering medium, a habitat for [[soil organisms]], a recycling system for [[nutrients]] and [[organic waste]]s, a regulator of [[water quality]], a modifier of [[Atmospheric chemistry|atmospheric composition]], and a medium for [[plant growth]], making it a critically important provider of [[ecosystem services]].<ref>{{cite journal |last1=Dominati |first1=Estelle |last2=Patterson |first2=Murray |last3=Mackay |first3=Alec |journal=[[Ecological Economics (journal)|Ecological Economics]] |volume=69 |issue=9 |title=A framework for classifying and quantifying the natural capital and ecosystem services of soils |year=2010 |url=https://www.researchgate.net/publication/223852147 |pages=1858‒68 |doi=10.1016/j.ecolecon.2010.05.002 |access-date=10 April 2022 |archive-url=https://web.archive.org/web/20170808082847/http://esanalysis.colmex.mx/Sorted%20Papers/2010/2010%20NZL%20-3F%20Phys.pdf |archive-date=8 August 2017 |url-status=live }}</ref> Since soil has a tremendous range of available [[Ecological niche|niches]] and [[habitat]]s, it contains a prominent part of the Earth's [[genetic diversity]]. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored.<ref>{{cite journal |last=Dykhuizen |first=Daniel E. |journal=Antonie van Leeuwenhoek |volume=73 |issue=1 |title=Santa Rosalia revisited: why are there so many species of bacteria? |year=1998 |url=https://www.researchgate.net/publication/13682480 |pages=25‒33 |doi=10.1023/A:1000665216662 |pmid=9602276 |s2cid=17779069 |access-date=10 April 2022 }}</ref><ref>{{cite journal |last1=Torsvik |first1=Vigdis |last2=Øvreås |first2=Lise |journal=[[Current Opinion in Microbiology]] |volume=5 |issue=3 |title=Microbial diversity and function in soil: from genes to ecosystems |year=2002 |pages=240‒45 |url=https://www.academia.edu/13038690 |doi=10.1016/S1369-5274(02)00324-7 |pmid=12057676 |access-date=10 April 2022 }}</ref> Soil has a [[mean]] [[Prokaryote|prokaryotic]] density of roughly 10<sup>8</sup> organisms per gram,<ref>{{cite journal |last1=Raynaud |first1=Xavier |last2=Nunan |first2=Naoise |journal=[[PLOS ONE]] |volume=9 |issue=1 |title=Spatial ecology of bacteria at the microscale in soil |year=2014 |page=e87217 |doi=10.1371/journal.pone.0087217 |pmid=24489873 |pmc=3905020 |bibcode=2014PLoSO...987217R |doi-access=free }}</ref> whereas the ocean has no more than 10<sup>7</sup> prokaryotic organisms per milliliter (gram) of seawater.<ref>{{cite journal |last1=Whitman |first1=William B. |last2=Coleman |first2=David C. |last3=Wiebe |first3=William J. |journal=[[Proceedings of the National Academy of Sciences of the USA]] |volume=95 |issue=12 |title=Prokaryotes: the unseen majority |year=1998 |pages=6578‒83 |doi=10.1073/pnas.95.12.6578 |pmid=9618454 |pmc=33863 |bibcode=1998PNAS...95.6578W |doi-access=free }}</ref> [[Soil organic matter|Organic carbon]] held in soil is eventually returned to the atmosphere through the process of [[cellular respiration|respiration]] carried out by [[heterotrophic]] organisms, but a substantial part is retained in the soil in the form of soil organic matter; [[tillage]] usually increases the rate of [[soil respiration]], leading to the depletion of soil organic matter.<ref>{{cite journal |last1=Schlesinger |first1=William H. |last2=Andrews |first2=Jeffrey A. |journal=Biogeochemistry |volume=48 |issue=1 |title=Soil respiration and the global carbon cycle |year=2000 |url=https://www.researchgate.net/publication/51997678 |pages=7‒20 |doi=10.1023/A:1006247623877 |s2cid=94252768 |access-date=10 April 2022 }}</ref> Since plant roots need oxygen, [[aeration]] is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected [[Pore space in soil|soil pores]], which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the [[Soil water (retention)|water-holding capacity]] of soils is vital for plant survival.<ref>{{cite journal |last1=Denmead |first1=Owen Thomas |last2=Shaw |first2=Robert Harold |journal=[[Agronomy Journal]] |volume=54 |issue=5 |title=Availability of soil water to plants as affected by soil moisture content and meteorological conditions |year=1962 |url=https://www.researchgate.net/publication/250098028 |pages=385‒90 |doi=10.2134/agronj1962.00021962005400050005x |access-date=10 April 2022 }}</ref> |
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A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas.<ref name="McClellan2017">{{cite web |last=McClellan |first=Tai |title=Soil composition |url=https://www.ctahr.hawaii.edu/mauisoil/a_comp.aspx |publisher=University of Hawai‘i at Mānoa, College of Tropical Agriculture and Human Resources |access-date=18 April 2022 }}</ref> The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other.<ref>{{cite web |title=Arizona Master Gardener Manual |url=http://ag.arizona.edu/pubs/garden/mg/soils/soils.html |publisher=Cooperative Extension, College of Agriculture, University of Arizona |access-date=17 December 2017 |url-status=dead |archive-url=https://web.archive.org/web/20160529015259/http://ag.arizona.edu/pubs/garden/mg/soils/soils.html |archive-date=29 May 2016 |date=9 November 2017 }}</ref> The pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil.<ref name="Vannier1987">{{cite journal |last=Vannier |first=Guy |journal=Biology and Fertility of Soils |volume=3 |issue=1 |title=The porosphere as an ecological medium emphasized in Professor Ghilarov's work on soil animal adaptations |year=1987 |url=https://link.springer.com/content/pdf/10.1007/BF00260577.pdf |pages=39–44 |doi=10.1007/BF00260577 |s2cid=297400 |access-date=18 April 2022 }}</ref> [[Soil compaction|Compaction]], a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms.<ref>{{cite journal |last1=Torbert |first1=H. Allen |last2=Wood |first2=Wes |journal=Communications in Soil Science and Plant Analysis |volume=23 |issue=11 |title=Effect of soil compaction and water-filled pore space on soil microbial activity and N losses |year=1992 |url=https://www.researchgate.net/publication/240546132 |pages=1321‒31 |doi=10.1080/00103629209368668 |access-date=18 April 2022 }}</ref> |
A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas.<ref name="McClellan2017">{{cite web |last=McClellan |first=Tai |title=Soil composition |url=https://www.ctahr.hawaii.edu/mauisoil/a_comp.aspx |publisher=University of Hawai‘i at Mānoa, College of Tropical Agriculture and Human Resources |access-date=18 April 2022 }}</ref> The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other.<ref>{{cite web |title=Arizona Master Gardener Manual |url=http://ag.arizona.edu/pubs/garden/mg/soils/soils.html |publisher=Cooperative Extension, College of Agriculture, University of Arizona |access-date=17 December 2017 |url-status=dead |archive-url=https://web.archive.org/web/20160529015259/http://ag.arizona.edu/pubs/garden/mg/soils/soils.html |archive-date=29 May 2016 |date=9 November 2017 }}</ref> The pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil.<ref name="Vannier1987">{{cite journal |last=Vannier |first=Guy |journal=Biology and Fertility of Soils |volume=3 |issue=1 |title=The porosphere as an ecological medium emphasized in Professor Ghilarov's work on soil animal adaptations |year=1987 |url=https://link.springer.com/content/pdf/10.1007/BF00260577.pdf |pages=39–44 |doi=10.1007/BF00260577 |s2cid=297400 |access-date=18 April 2022 }}</ref> [[Soil compaction|Compaction]], a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms.<ref>{{cite journal |last1=Torbert |first1=H. Allen |last2=Wood |first2=Wes |journal=Communications in Soil Science and Plant Analysis |volume=23 |issue=11 |title=Effect of soil compaction and water-filled pore space on soil microbial activity and N losses |year=1992 |url=https://www.researchgate.net/publication/240546132 |pages=1321‒31 |doi=10.1080/00103629209368668 |access-date=18 April 2022 }}</ref> |
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Given sufficient time, an undifferentiated soil will evolve a [[soil horizon|soil profile]] which consists of two or more layers, referred to as soil horizons. These differ in one or more properties such as in their [[Soil texture|texture]], [[structure]], [[density]], porosity, consistency, temperature, color, and [[Reactivity (chemistry)|reactivity]].<ref name="Buol"/> The horizons differ greatly in thickness and generally lack sharp boundaries; their development is dependent on the type of [[parent material]], the processes that modify those parent materials, and the [[#soil-forming factors|soil-forming factors]] that influence those processes. The biological influences on soil properties are strongest near the surface, |
Given sufficient time, an undifferentiated soil will evolve a [[soil horizon|soil profile]] which consists of two or more layers, referred to as soil horizons. These differ in one or more properties such as in their [[Soil texture|texture]], [[structure]], [[density]], porosity, consistency, temperature, color, and [[Reactivity (chemistry)|reactivity]].<ref name="Buol"/> The horizons differ greatly in thickness and generally lack sharp boundaries; their development is dependent on the type of [[parent material]], the processes that modify those parent materials, and the [[#soil-forming factors|soil-forming factors]] that influence those processes. The biological influences on soil properties are strongest near the surface, though the geochemical influences on soil properties increase with depth. Mature soil profiles typically include three basic master horizons: A, B, and C. The [[solum]] normally includes the A and B horizons. The living component of the soil is largely confined to the solum, and is generally more prominent in the A horizon.{{sfn|Simonson|1957|p=17}} It has been suggested that the ''pedon'', a column of soil extending vertically from the surface to the underlying parent material and large enough to show the characteristics of all its horizons, could be subdivided in the ''humipedon'' (the living part, where most soil organisms are dwelling, corresponding to the ''humus form''), the ''copedon'' (in intermediary position, where most [[weathering]] of minerals takes place) and the ''lithopedon'' (in contact with the subsoil).<ref>{{cite journal |last1=Zanella |first1=Augusto |last2=Katzensteiner |first2=Klaus |last3=Ponge |first3=Jean-François |last4=Jabiol |first4=Bernard |last5=Sartori |first5=Giacomo |last6=Kolb |first6=Eckart |last7=Le Bayon |first7=Renée-Claire |last8=Aubert |first8=Michaël |last9=Ascher-Jenull |first9=Judith |last10=Englisch |first10=Michael |last11=Hager |first11=Herbert |title=TerrHum: an iOS App for classifying terrestrial humipedons and some considerations about soil classification |journal=[[Soil Science Society of America Journal]] |date=June 2019 |volume=83 |issue=S1 |pages=S42–S48 |doi=10.2136/sssaj2018.07.0279 |s2cid=197555747 |url=https://www.researchgate.net/publication/332080061 |access-date=18 April 2022 }}</ref> |
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The soil texture is determined by the relative proportions of the individual particles of [[sand]], [[silt]], and [[clay]] that make up the soil. The interaction of the individual mineral particles with organic matter, water, gases via [[Biotic component|biotic]] and [[abiotic]] processes causes those particles to [[flocculate]] (stick together) to form [[soil structure|aggregates]] or [[ped]]s.<ref name="Bronick2005">{{cite journal |last1=Bronick |first1=Carol J. |last2=Lal |first2=Ratan |title=Soil structure and management: a review |journal=Geoderma |date=January 2005 |volume=124 |issue=1–2 |pages=3–22 |doi=10.1016/j.geoderma.2004.03.005 |url=http://tinread.usarb.md:8888/tinread/fulltext/lal/soil_structure.pdf |access-date=18 April 2022 |bibcode=2005Geode.124....3B }}</ref> Where these aggregates can be identified, a soil can be said to be developed, and can be described further in terms of color, porosity, consistency, reaction ([[acidity]]), etc. |
The soil texture is determined by the relative proportions of the individual particles of [[sand]], [[silt]], and [[clay]] that make up the soil. The interaction of the individual mineral particles with organic matter, water, gases via [[Biotic component|biotic]] and [[abiotic]] processes causes those particles to [[flocculate]] (stick together) to form [[soil structure|aggregates]] or [[ped]]s.<ref name="Bronick2005">{{cite journal |last1=Bronick |first1=Carol J. |last2=Lal |first2=Ratan |title=Soil structure and management: a review |journal=Geoderma |date=January 2005 |volume=124 |issue=1–2 |pages=3–22 |doi=10.1016/j.geoderma.2004.03.005 |url=http://tinread.usarb.md:8888/tinread/fulltext/lal/soil_structure.pdf |access-date=18 April 2022 |bibcode=2005Geode.124....3B }}</ref> Where these aggregates can be identified, a soil can be said to be developed, and can be described further in terms of color, porosity, consistency, reaction ([[acidity]]), etc. |
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Water is a critical agent in soil development due to its involvement in the dissolution, precipitation, erosion, transport, and deposition of the materials of which a soil is composed.<ref>{{cite web |url=https://www.fao.org/3/r4082e/r4082e03.htm |title=Soil and water |website=[[Food and Agriculture Organization of the United Nations]] |access-date=18 April 2022 }}</ref> The mixture of water and dissolved or suspended materials that occupy the soil [[pore space]] is called the soil solution. Since soil water is never pure water, but contains hundreds of dissolved organic and mineral substances, it may be more accurately called the soil solution. Water is central to the [[Dissolution (chemistry)|dissolution]], [[Precipitation (chemistry)|precipitation]] and [[Leaching (agriculture)|leaching]] of minerals from the [[soil profile]]. Finally, water affects the type of vegetation that grows in a soil, which in turn affects the development of the soil, a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi-arid regions.<ref>{{cite journal |last1=Valentin |first1=Christian |last2=d'Herbès |first2=Jean-Marc |last3=Poesen |first3=Jean |journal=Catena |volume=37 |issue=1 |title=Soil and water components of banded vegetation patterns |year=1999 |url=https://www.academia.edu/35300713 |pages=1‒24 |doi=10.1016/S0341-8162(99)00053-3 |access-date=18 April 2022 }}</ref> |
Water is a critical agent in soil development due to its involvement in the dissolution, precipitation, erosion, transport, and deposition of the materials of which a soil is composed.<ref>{{cite web |url=https://www.fao.org/3/r4082e/r4082e03.htm |title=Soil and water |website=[[Food and Agriculture Organization of the United Nations]] |access-date=18 April 2022 }}</ref> The mixture of water and dissolved or suspended materials that occupy the soil [[pore space]] is called the soil solution. Since soil water is never pure water, but contains hundreds of dissolved organic and mineral substances, it may be more accurately called the soil solution. Water is central to the [[Dissolution (chemistry)|dissolution]], [[Precipitation (chemistry)|precipitation]] and [[Leaching (agriculture)|leaching]] of minerals from the [[soil profile]]. Finally, water affects the type of vegetation that grows in a soil, which in turn affects the development of the soil, a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi-arid regions.<ref>{{cite journal |last1=Valentin |first1=Christian |last2=d'Herbès |first2=Jean-Marc |last3=Poesen |first3=Jean |journal=Catena |volume=37 |issue=1 |title=Soil and water components of banded vegetation patterns |year=1999 |url=https://www.academia.edu/35300713 |pages=1‒24 |doi=10.1016/S0341-8162(99)00053-3 |access-date=18 April 2022 }}</ref> |
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Soils supply plants with [[nutrient]]s, most of which are held in place by particles of [[Soil texture#Soil separates|clay]] and organic matter ([[colloid]]s)<ref>{{cite book |last1=Brady |first1=Nyle C. |last2=Weil |first2=Ray R. |date=2007 |chapter=The colloidal fraction: seat of soil chemical and physical activity |title=The nature and properties of soils |pages=310–357 |edition=14th |editor-last1=Brady |editor-first1=Nyle C. |editor-last2=Weil |editor-first2=Ray R. |publisher=[[Pearson Education|Pearson]] |location=London, United Kingdom |isbn=978-0132279383 |chapter-url=https://www.researchgate.net/publication/309630422 |access-date=18 April 2022 }}</ref> The nutrients may be [[Adsorption|adsorbed]] on clay mineral surfaces, bound within clay minerals ([[Absorption (chemistry)|absorbed]]), or bound within organic compounds as part of the living [[Soil organism|organisms]] or dead soil organic matter. These bound nutrients interact with soil water to [[Buffer solution|buffer]] the soil solution composition (attenuate changes in the soil solution) as soils wet up or dry out, as plants take up nutrients, as salts are leached, or as acids or alkalis are added.<ref>{{cite web |url=http://eagri.org/eagri50/SSAC121/lec14.pdf |title=Soil colloids: properties, nature, types and significance |website=[[Tamil Nadu Agricultural University]] |access-date=18 April 2022 }}</ref> |
Soils supply [[Plant|plants]] with [[nutrient]]s, most of which are held in place by particles of [[Soil texture#Soil separates|clay]] and organic matter ([[colloid]]s)<ref>{{cite book |last1=Brady |first1=Nyle C. |last2=Weil |first2=Ray R. |date=2007 |chapter=The colloidal fraction: seat of soil chemical and physical activity |title=The nature and properties of soils |pages=310–357 |edition=14th |editor-last1=Brady |editor-first1=Nyle C. |editor-last2=Weil |editor-first2=Ray R. |publisher=[[Pearson Education|Pearson]] |location=London, United Kingdom |isbn=978-0132279383 |chapter-url=https://www.researchgate.net/publication/309630422 |access-date=18 April 2022 }}</ref> The nutrients may be [[Adsorption|adsorbed]] on clay mineral surfaces, bound within clay minerals ([[Absorption (chemistry)|absorbed]]), or bound within organic compounds as part of the living [[Soil organism|organisms]] or dead soil organic matter. These bound nutrients interact with soil water to [[Buffer solution|buffer]] the soil solution composition (attenuate changes in the soil solution) as soils wet up or dry out, as plants take up nutrients, as salts are leached, or as acids or alkalis are added.<ref>{{cite web |url=http://eagri.org/eagri50/SSAC121/lec14.pdf |title=Soil colloids: properties, nature, types and significance |website=[[Tamil Nadu Agricultural University]] |access-date=18 April 2022 }}</ref> |
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Plant nutrient availability is affected by [[soil pH]], which is a measure of the [[hydrogen]] [[Thermodynamic activity|ion activity]] in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acid) where weathering is more advanced.<ref>{{cite web |url=https://www.researchgate.net/publication/305775103 |last=Miller |first=Jarrod O. |title=Soil pH affects nutrient availability |access-date=18 April 2022 }}</ref> |
Plant nutrient availability is affected by [[soil pH]], which is a measure of the [[hydrogen]] [[Thermodynamic activity|ion activity]] in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acid) where weathering is more advanced.<ref>{{cite web |url=https://www.researchgate.net/publication/305775103 |last=Miller |first=Jarrod O. |title=Soil pH affects nutrient availability |access-date=18 April 2022 }}</ref> |
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==Formation== |
==Formation== |
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{{main|Soil |
{{main|Soil formation}} |
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{{Further|Soil mechanics#Genesis}} |
{{Further|Soil mechanics#Genesis}} |
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Soil is said to be formed when organic matter has accumulated and colloids are washed downward, leaving deposits of clay, [[humus]], [[iron oxide]], [[carbonate]], and [[gypsum]], producing a distinct layer called the B horizon. This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time.<ref>{{cite journal |last1=Sengupta |first1=Aditi |last2=Kushwaha |first2=Priyanka |last3=Jim |first3=Antonia |last4=Troch |first4= Peter A. |last5=Maier |first5=Raina |date=2020 |title=New soil, old plants, and ubiquitous microbes: evaluating the potential of incipient basaltic soil to support native plant growth and influence belowground soil microbial community composition |journal=[[Sustainability (journal)|Sustainability]] |volume=12 |issue=10 |pages=4209 |doi=10.3390/su12104209 |doi-access=free }}</ref> These constituents are moved from one level to another by water and animal activity. As a result, layers (horizons) form in the soil profile. The alteration and movement of materials within a soil causes the formation of distinctive [[soil horizons]]. However, more recent definitions of soil embrace soils without any organic matter, such as those [[regolith]]s that formed on Mars<ref>{{cite journal |last1=Bishop |first1=Janice L. |last2=Murchie |first2=Scott L. |last3=Pieters |first3=Carlé L. |last4=Zent |first4=Aaron P. |date=2002 |title=A model for formation of dust, soil, and rock coatings on Mars: physical and chemical processes on the Martian surface |journal=[[Journal of Geophysical Research]] |volume=107 |issue=E11 |pages=7-1–7-17 |doi=10.1029/2001JE001581 |bibcode=2002JGRE..107.5097B |doi-access=free }}</ref> and analogous conditions in planet Earth deserts.<ref>{{cite journal |last1=Navarro-González |first1=Rafael |last2=Rainey |first2=Fred A. |last3=Molina |first3=Paola |last4=Bagaley |first4=Danielle R. |last5=Hollen |first5=Becky J. |last6=de la Rosa |first6=José |last7=Small |first7=Alanna M. |last8=Quinn |first8=Richard C. |last9=Grunthaner |first9=Frank J. |last10=Cáceres |first10=Luis |last11=Gomez-Silva |first11=Benito |last12=McKay |first12=Christopher P. |date=2003 |title=Mars-like soils in the Atacama desert, Chile, and the dry limit of microbial life |journal=[[Science (journal)|Science]] |volume=302 |issue=5647 |pages=1018–1021 |doi=10.1126/science.1089143 |pmid=14605363 |url=https://www.researchgate.net/publication/9020258 |access-date=24 April 2022 |bibcode=2003Sci...302.1018N |s2cid=18220447 }}</ref> |
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An example of the development of a soil would begin with the weathering of lava flow bedrock, which would produce the purely mineral-based parent material from which the soil texture forms. Soil development would proceed most rapidly from bare rock of recent flows in a warm climate, under heavy and frequent rainfall. Under such conditions, plants (in a first stage [[nitrogen-fixing]] [[lichens]] and [[cyanobacteria]] then [[epilithic]] [[higher plants]]) become established very quickly on [[basalt]]ic lava, even though there is very little organic material.<ref>{{cite journal |last1=Guo |first1=Yong |last2=Fujimura |first2=Reiko |last3=Sato |first3=Yoshinori |last4=Suda |first4=Wataru |last5=Kim |first5=Seok-won |last6=Oshima |first6=Kenshiro |last7=Hattori |first7=Masahira |last8=Kamijo |first8=Takashi |last9=Narisawa |first9=Kazuhiko |last10=Ohta |first10=Hiroyuki |date=2014 |title=Characterization of early microbial communities on volcanic deposits along a vegetation gradient on the island of Miyake, Japan |journal=Microbes and Environments |volume=29 |issue=1 |pages=38–49 |doi=10.1264/jsme2.ME13142 |pmid=24463576 |pmc=4041228 |doi-access=free }}</ref> Basaltic minerals commonly weather relatively quickly, according to the [[Goldich dissolution series]].<ref>{{cite journal|last=Goldich |first=Samuel S. |date=1938 |title=A study in rock-weathering |url=https://fr.art1lib.org/book/60175497/a54b2b |journal=[[The Journal of Geology]] |volume=46 |issue=1 |pages=17–58 |bibcode=1938JG.....46...17G |doi=10.1086/624619 |issn=0022-1376 |access-date=24 April 2022 |s2cid=128498195 }}</ref> The plants are supported by the porous rock as it is filled with nutrient-bearing water that carries minerals dissolved from the rocks. Crevasses and pockets, local topography of the rocks, would hold fine materials and harbour plant roots. The developing plant roots are associated with mineral-weathering [[Mycorrhiza|mycorrhizal fungi]]<ref name="Van Schöll2006">{{cite journal |last1=Van Schöll |first1=Laura |last2=Smits |first2=Mark M. |last3=Hoffland |first3=Ellis |date=2006 |title=Ectomycorrhizal weathering of the soil minerals muscovite and hornblende |journal=[[New Phytologist]] |volume=171 |issue=4 |pages=805–814 |doi=10.1111/j.1469-8137.2006.01790.x |pmid=16918551 |doi-access=free }}</ref> that assist in breaking up the porous lava, and by these means organic matter and a finer mineral soil accumulate with time. Such initial stages of soil development have been described on volcanoes,<ref>{{cite journal |last1=Stretch |first1=Rachelle C. |last2=Viles |first2=Heather A. |year=2002 |title=The nature and rate of weathering by lichens on lava flows on Lanzarote |journal=[[Geomorphology (journal)|Geomorphology]] |volume=47 |issue=1 |pages=87–94 |doi=10.1016/S0169-555X(02)00143-5 |bibcode=2002Geomo..47...87S |url=https://fr.art1lib.org/book/17831662/8253cd |access-date=24 April 2022 }}</ref> inselbergs,<ref>{{cite journal |last1=Dojani |first1=Stephanie |last2=Lakatos |first2=Michael |last3=Rascher |first3=Uwe |last4=Waneck |first4=Wolfgang |last5=Luettge |first5=Ulrich |last6=Büdel |first6=Burkhard |year=2007 |title=Nitrogen input by cyanobacterial biofilms of an inselberg into a tropical rainforest in French Guiana |journal=Flora |volume=202 |issue=7 |pages=521–529 |doi=10.1016/j.flora.2006.12.001 |url=https://www.researchgate.net/publication/224026482 |access-date=21 March 2021}}</ref> and glacial moraines.<ref>{{cite journal |last1=Kabala |first1=Cesary |last2=Kubicz |first2=Justyna |year=2012 |title=Initial soil development and carbon accumulation on moraines of the rapidly retreating Werenskiold Glacier, SW Spitsbergen, Svalbard archipelago |journal=Geoderma |volume=175–176 |pages=9–20 |url=https://www.academia.edu/31221217 |doi=10.1016/j.geoderma.2012.01.025 |access-date=24 April 2022 |bibcode=2012Geode.175....9K }}</ref> |
An example of the development of a soil would begin with the weathering of lava flow bedrock, which would produce the purely mineral-based parent material from which the soil texture forms. Soil development would proceed most rapidly from bare rock of recent flows in a warm climate, under heavy and frequent rainfall. Under such conditions, plants (in a first stage [[nitrogen-fixing]] [[lichens]] and [[cyanobacteria]] then [[epilithic]] [[higher plants]]) become established very quickly on [[basalt]]ic lava, even though there is very little organic material.<ref>{{cite journal |last1=Guo |first1=Yong |last2=Fujimura |first2=Reiko |last3=Sato |first3=Yoshinori |last4=Suda |first4=Wataru |last5=Kim |first5=Seok-won |last6=Oshima |first6=Kenshiro |last7=Hattori |first7=Masahira |last8=Kamijo |first8=Takashi |last9=Narisawa |first9=Kazuhiko |last10=Ohta |first10=Hiroyuki |date=2014 |title=Characterization of early microbial communities on volcanic deposits along a vegetation gradient on the island of Miyake, Japan |journal=Microbes and Environments |volume=29 |issue=1 |pages=38–49 |doi=10.1264/jsme2.ME13142 |pmid=24463576 |pmc=4041228 |doi-access=free }}</ref> Basaltic minerals commonly weather relatively quickly, according to the [[Goldich dissolution series]].<ref>{{cite journal|last=Goldich |first=Samuel S. |date=1938 |title=A study in rock-weathering |url=https://fr.art1lib.org/book/60175497/a54b2b |journal=[[The Journal of Geology]] |volume=46 |issue=1 |pages=17–58 |bibcode=1938JG.....46...17G |doi=10.1086/624619 |issn=0022-1376 |access-date=24 April 2022 |s2cid=128498195 }}</ref> The plants are supported by the porous rock as it is filled with nutrient-bearing water that carries minerals dissolved from the rocks. Crevasses and pockets, local topography of the rocks, would hold fine materials and harbour plant roots. The developing plant roots are associated with mineral-weathering [[Mycorrhiza|mycorrhizal fungi]]<ref name="Van Schöll2006">{{cite journal |last1=Van Schöll |first1=Laura |last2=Smits |first2=Mark M. |last3=Hoffland |first3=Ellis |date=2006 |title=Ectomycorrhizal weathering of the soil minerals muscovite and hornblende |journal=[[New Phytologist]] |volume=171 |issue=4 |pages=805–814 |doi=10.1111/j.1469-8137.2006.01790.x |pmid=16918551 |doi-access=free }}</ref> that assist in breaking up the porous lava, and by these means organic matter and a finer mineral soil accumulate with time. Such initial stages of soil development have been described on volcanoes,<ref>{{cite journal |last1=Stretch |first1=Rachelle C. |last2=Viles |first2=Heather A. |year=2002 |title=The nature and rate of weathering by lichens on lava flows on Lanzarote |journal=[[Geomorphology (journal)|Geomorphology]] |volume=47 |issue=1 |pages=87–94 |doi=10.1016/S0169-555X(02)00143-5 |bibcode=2002Geomo..47...87S |url=https://fr.art1lib.org/book/17831662/8253cd |access-date=24 April 2022 }}</ref> inselbergs,<ref>{{cite journal |last1=Dojani |first1=Stephanie |last2=Lakatos |first2=Michael |last3=Rascher |first3=Uwe |last4=Waneck |first4=Wolfgang |last5=Luettge |first5=Ulrich |last6=Büdel |first6=Burkhard |year=2007 |title=Nitrogen input by cyanobacterial biofilms of an inselberg into a tropical rainforest in French Guiana |journal=Flora |volume=202 |issue=7 |pages=521–529 |doi=10.1016/j.flora.2006.12.001 |url=https://www.researchgate.net/publication/224026482 |access-date=21 March 2021}}</ref> and glacial moraines.<ref>{{cite journal |last1=Kabala |first1=Cesary |last2=Kubicz |first2=Justyna |year=2012 |title=Initial soil development and carbon accumulation on moraines of the rapidly retreating Werenskiold Glacier, SW Spitsbergen, Svalbard archipelago |journal=Geoderma |volume=175–176 |pages=9–20 |url=https://www.academia.edu/31221217 |doi=10.1016/j.geoderma.2012.01.025 |access-date=24 April 2022 |bibcode=2012Geode.175....9K }}</ref> |
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How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil |
How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil: 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=24 April 2022 |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, relief, organisms, parent material, and time, they form the acronym CROPT.<ref>{{cite web |url=http://www.tsu-excel4ed.org/reviews/Geography%20Template_The%20Physical%20Environment_Cunha.pdf |title=The physical environment: an introduction to physical geography |first=Michael E. |last=Ritter |access-date=24 April 2022 }}</ref> |
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==Physical properties== |
==Physical properties== |
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{{main|Physical properties of soil}} |
{{main|Physical properties of soil}} |
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{{for|the |
{{for|the academic discipline|Soil physics}} |
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The physical properties of soils, in order of decreasing importance for ecosystem services such as [[crop production]], are texture, structure, [[bulk density]], porosity, consistency, temperature, colour and [[Soil resistivity|resistivity]].<ref>{{cite book |last1=Gardner |first1=Catriona M.K. |last2=Laryea |first2=Kofi Buna |last3=Unger |first3=Paul W. |date=1999 |title=Soil physical constraints to plant growth and crop production |edition=1st |location=Rome |publisher=[[Food and Agriculture Organization of the United Nations]] |url=http://plantstress.com/Files/Soil_Physical_Constraints.pdf |access-date=24 December 2017 |archive-url=https://web.archive.org/web/20170808175354/http://www.plantstress.com/Files/Soil_Physical_Constraints.pdf |archive-date=8 August 2017 |url-status=dead}}</ref> Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly ''soil aggregates'' are created from the soil separates when iron oxides, carbonates, clay, [[silica]] and humus, coat particles and cause them to adhere into larger, relatively [[Soil aggregate stability|stable]] secondary structures.<ref>{{cite journal |last1=Six |first1=Johan |last2=Paustian |first2=Keith |last3=Elliott |first3=Edward T. |last4=Combrink |first4=Clay |journal=[[Soil Science Society of America Journal]] |volume=64 |issue=2 |title=Soil structure and organic matter. I. Distribution of aggregate-size classes and aggregate-associated carbon |url=https://www.researchgate.net/publication/280798601 |year=2000 |pages=681–689 |doi=10.2136/sssaj2000.642681x |access-date=28 March 2021 |bibcode=2000SSASJ..64..681S}}</ref> Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction.<ref>{{cite journal |last1=Håkansson |first1=Inge |last2=Lipiec |first2=Jerzy |journal=Soil and Tillage Research |volume=53 |issue=2 |title=A review of the usefulness of relative bulk density values in studies of soil structure and compaction |url=http://directory.umm.ac.id/Data%20Elmu/jurnal/S/Soil%20&%20Tillage%20Research/Vol53.Issue2.Jan2000/1452.pdf |year=2000 |pages=71–85 |doi=10.1016/S0167-1987(99)00095-1 |s2cid=30045538 |access-date=28 March 2021}}</ref> Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil.<ref>{{cite journal |last=Schwerdtfeger |first=W.J. |journal=[[Journal of Research of the National Bureau of Standards]] |volume=69C |issue=1 |title=Soil resistivity as related to underground corrosion and cathodic protection |year=1965 |pages=71–77 |doi=10.6028/jres.069c.012 |doi-access=free}}</ref> These properties vary through the depth of a soil profile, i.e. through soil horizons. Most of these properties determine the aeration of the soil and the ability of water to infiltrate and to be held within the soil.<ref>{{cite book |last=Tamboli |first=Prabhakar Mahadeo |date=1961 |title=The influence of bulk density and aggregate size on soil moisture retention |location=Ames, Iowa |publisher=[[Iowa State University]] |url=http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3448&context=rtd |access-date=28 March 2021}}</ref> |
The physical properties of soils, in order of decreasing importance for ecosystem services such as [[crop production]], are texture, structure, [[bulk density]], porosity, consistency, temperature, colour and [[Soil resistivity|resistivity]].<ref>{{cite book |last1=Gardner |first1=Catriona M.K. |last2=Laryea |first2=Kofi Buna |last3=Unger |first3=Paul W. |date=1999 |title=Soil physical constraints to plant growth and crop production |edition=1st |location=Rome |publisher=[[Food and Agriculture Organization of the United Nations]] |url=http://plantstress.com/Files/Soil_Physical_Constraints.pdf |access-date=24 December 2017 |archive-url=https://web.archive.org/web/20170808175354/http://www.plantstress.com/Files/Soil_Physical_Constraints.pdf |archive-date=8 August 2017 |url-status=dead}}</ref> Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly ''soil aggregates'' are created from the soil separates when iron oxides, carbonates, clay, [[silica]] and humus, coat particles and cause them to adhere into larger, relatively [[Soil aggregate stability|stable]] secondary structures.<ref>{{cite journal |last1=Six |first1=Johan |last2=Paustian |first2=Keith |last3=Elliott |first3=Edward T. |last4=Combrink |first4=Clay |journal=[[Soil Science Society of America Journal]] |volume=64 |issue=2 |title=Soil structure and organic matter. I. Distribution of aggregate-size classes and aggregate-associated carbon |url=https://www.researchgate.net/publication/280798601 |year=2000 |pages=681–689 |doi=10.2136/sssaj2000.642681x |access-date=28 March 2021 |bibcode=2000SSASJ..64..681S}}</ref> Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction.<ref>{{cite journal |last1=Håkansson |first1=Inge |last2=Lipiec |first2=Jerzy |journal=Soil and Tillage Research |volume=53 |issue=2 |title=A review of the usefulness of relative bulk density values in studies of soil structure and compaction |url=http://directory.umm.ac.id/Data%20Elmu/jurnal/S/Soil%20&%20Tillage%20Research/Vol53.Issue2.Jan2000/1452.pdf |year=2000 |pages=71–85 |doi=10.1016/S0167-1987(99)00095-1 |s2cid=30045538 |access-date=28 March 2021}}</ref> Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil.<ref>{{cite journal |last=Schwerdtfeger |first=W.J. |journal=[[Journal of Research of the National Bureau of Standards]] |volume=69C |issue=1 |title=Soil resistivity as related to underground corrosion and cathodic protection |year=1965 |pages=71–77 |doi=10.6028/jres.069c.012 |doi-access=free}}</ref> These properties vary through the depth of a soil profile, i.e. through soil horizons. Most of these properties determine the aeration of the soil and the ability of water to infiltrate and to be held within the soil.<ref>{{cite book |last=Tamboli |first=Prabhakar Mahadeo |date=1961 |title=The influence of bulk density and aggregate size on soil moisture retention |location=Ames, Iowa |publisher=[[Iowa State University]] |url=http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3448&context=rtd |access-date=28 March 2021}}</ref> |
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==Soil moisture== |
==Soil moisture== |
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{{Main|Soil moisture}}{{Expand section|This section should have a longer summary of the main article|date=May 2022}} |
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{{Main|Soil moisture}} |
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Soil [[water content]] can be measured as volume or [[Specific_weight#Soil_mechanics|weight]]. Soil moisture levels, in order of decreasing water content, are saturation, [[field capacity]], [[wilting point]], air dry, and oven dry. Field capacity describes a drained wet soil at the point water content reaches equilibrium with gravity. Irrigating soil above field capacity risks percolation losses. Wilting point describes the dry limit for growing plants. |
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[[Available water capacity]] is the amount of water held in a soil profile available to plants. As water content drops, plants have to work against increasing forces of adherence and [[sorptivity]] to withdraw water. [[Irrigation scheduling]] avoids [[moisture stress]] by replenishing depleted water before stress is induced.<ref>{{cite web|title=Water holding capacity|work=Oregon State University|url=https://forages.oregonstate.edu/ssis/soils/characteristics/water-holding-capacity|quote=Irrigators must have knowledge of the readily available moisture capacity so that water can be applied before plants have to expend excessive energy to extract moisture.}}</ref><ref>{{cite web|title=Basics of irrigation scheduling|work=University of Minnesota Extension|url=https://extension.umn.edu/irrigation/basics-irrigation-scheduling|quote=Only a portion of the available water holding capacity is easily used by the crop before crop water stress develop}}</ref> |
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[[Capillary action]] is responsible for moving [[groundwater]] from wet regions of the soil to dry areas. [[Subirrigation]] designs (e.g., [[wicking bed]]s, [[sub-irrigated planter]]s) rely on capillarity to supply water to plant roots. Capillary action can result in an evaporative concentration of salts, causing land degradation through [[Soil_salinity#Dry_land_salinity|salination]]. |
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==Soil gas== |
==Soil gas== |
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{{main|Soil gas}} |
{{main|Soil gas}} |
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The atmosphere of soil, or [[soil gas]], is very different from the atmosphere above. The consumption of oxygen by microbes and plant roots, and their release of carbon dioxide, |
The atmosphere of soil, or [[soil gas]], is very different from the atmosphere above. The consumption of oxygen by microbes and plant roots, and their release of carbon dioxide, decreases oxygen and increases carbon dioxide concentration. Atmospheric CO<sub>2</sub> concentration is 0.04%, but in the soil pore space it may range from 10 to 100 times that level, thus potentially contributing to the inhibition of root respiration.<ref>{{cite journal |last1=Qi |first1=Jingen |last2=Marshall |first2=John D. |last3=Mattson |first3=Kim G. |journal=[[New Phytologist]] |volume=128 |issue=3 |title=High soil carbon dioxide concentrations inhibit root respiration of Douglas fir |year=1994 |pages=435–442 |doi=10.1111/j.1469-8137.1994.tb02989.x |pmid=33874575 |doi-access=free}}</ref> Calcareous soils regulate CO<sub>2</sub> concentration by [[carbonate]] [[Buffering agent|buffering]], contrary to acid soils in which all CO<sub>2</sub> respired accumulates in the soil pore system.<ref>{{cite journal |last1=Karberg |first1=Noah J. |last2=Pregitzer |first2=Kurt S. |last3=King |first3=John S. |last4=Friend |first4=Aaron L. |last5=Wood |first5=James R. |journal=[[Oecologia]] |volume=142 |issue=2 |title=Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone |url=https://www.nrs.fs.fed.us/pubs/jrnl/2004/nc_2004_Karberg_001.pdf |year=2005 |pages=296–306 |doi=10.1007/s00442-004-1665-5 |pmid=15378342 |access-date=25 April 2021 |bibcode=2005Oecol.142..296K |s2cid=6161016 }}</ref> At extreme levels, CO<sub>2</sub> is toxic.<ref>{{cite journal |last1=Chang |first1=H.T. |last2=Loomis |first2=W.E. |journal=[[Plant Physiology (journal)|Plant Physiology]] |volume=20 |issue=2 |title=Effect of carbon dioxide on absorption of water and nutrients by roots |year=1945 |pages=221–232 |doi=10.1104/pp.20.2.221 |pmid=16653979 |pmc=437214}}</ref> This suggests a possible [[negative feedback]] control of soil CO<sub>2</sub> concentration through its inhibitory effects on root and microbial respiration (also called 'soil respiration').<ref>{{cite journal |last1=McDowell |first1=Nate J. |last2=Marshall |first2=John D. |last3=Qi |first3=Jingen |last4=Mattson |first4=Kim |journal=Tree Physiology |volume=19 |issue=9 |title=Direct inhibition of maintenance respiration in western hemlock roots exposed to ambient soil carbon dioxide concentrations |url=https://www.researchgate.net/publication/10842414 |year=1999 |pages=599–605 |doi=10.1093/treephys/19.9.599 |pmid=12651534 |doi-access=free}}</ref> In addition, the soil voids are saturated with water vapour, at least until the point of maximal [[hygroscopic]]ity, beyond which a [[vapour-pressure deficit]] occurs in the soil pore space.<ref name="Vannier1987"/> Adequate porosity is necessary, not just to allow the penetration of water, but also to allow gases to diffuse in and out. Movement of gases is by [[diffusion]] from high concentrations to lower, the [[diffusion coefficient]] decreasing with soil compaction.<ref>{{cite journal |last1=Xu |first1=Xia |last2=Nieber |first2=John L. |last3=Gupta |first3=Satish C. |journal=[[Soil Science Society of America Journal]] |volume=56 |issue=6 |title=Compaction effect on the gas diffusion coefficient in soils |url=https://www.academia.edu/6547475 |year=1992 |pages=1743–1750 |doi=10.2136/sssaj1992.03615995005600060014x |access-date=25 April 2021 |bibcode=1992SSASJ..56.1743X}}</ref> Oxygen from above atmosphere diffuses in the soil where it is consumed and levels of carbon dioxide in excess of above atmosphere diffuse out with other gases (including [[greenhouse gases]]) as well as water.<ref name="Smith2003">{{cite journal |last1=Smith |first1=Keith A. |last2=Ball |first2=Tom |last3=Conen |first3=Franz |last4=Dobbie |first4=Karen E. |last5=Massheder |first5=Jonathan |last6=Rey |first6=Ana |journal=European Journal of Soil Science |volume=54 |issue=4 |title=Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes |url=https://www.academia.edu/14433607 |year=2003 |pages=779–791 |doi=10.1046/j.1351-0754.2003.0567.x |s2cid=18442559 |access-date=25 April 2021}}</ref> Soil texture and structure strongly affect soil porosity and gas diffusion. It is the total pore space ([[porosity]]) of soil, not the pore size, and the degree of pore interconnection (or conversely pore sealing), together with water content, air [[turbulence]] and temperature, that determine the rate of diffusion of gases into and out of soil.{{sfn|Russell|1957|pp=35–36}}<ref name="Smith2003"/> [[Ped#Platy|Platy]] soil structure and soil compaction (low porosity) impede gas flow, and a deficiency of oxygen may encourage anaerobic bacteria to reduce (strip oxygen) from nitrate NO<sub>3</sub> to the gases N<sub>2</sub>, N<sub>2</sub>O, and NO, which are then lost to the atmosphere, thereby depleting the soil of nitrogen, a detrimental process called [[denitrification]].<ref>{{cite journal |last1=Ruser |first1=Reiner |last2=Flessa |first2=Heiner |last3=Russow |first3=Rolf |last4=Schmidt |first4=G. |last5=Buegger |first5=Franz |last6=Munch |first6=J.C. |journal=[[Soil Biology and Biochemistry]] |volume=38 |issue=2 |title=Emission of N<sub>2</sub>O, N<sub>2</sub> and CO<sub>2</sub> from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting |url=https://www.uni-hohenheim.de/qisserver/rds?state=medialoader&objectid=851&application=lsf |year=2006 |pages=263–274 |doi=10.1016/j.soilbio.2005.05.005 |access-date=25 April 2021}}</ref> Aerated soil is also a net sink of methane (CH<sub>4</sub>)<ref>{{cite journal |last1=Hartmann |first1=Adrian A. |last2=Buchmann |first2=Nina |last3=Niklaus |first3=Pascal A. |journal=[[Plant and Soil]] |volume=342 |issue=1–2 |title=A study of soil methane sink regulation in two grasslands exposed to drought and N fertilization |year=2011 |pages=265–275 |doi=10.1007/s11104-010-0690-x |hdl=20.500.11850/34759 |s2cid=25691034 |doi-access=free}}</ref> but a net producer of methane (a strong heat-absorbing [[greenhouse gas]]) when soils are depleted of oxygen and subject to elevated temperatures.<ref>{{cite journal |last1=Moore |first1=Tim R. |last2=Dalva |first2=Moshe |journal=Journal of Soil Science |volume=44 |issue=4 |title=The influence of temperature and water table position on carbon dioxide and methane emissions from laboratory columns of peatland soils |url=https://www.researchgate.net/publication/229878721 |year=1993 |pages=651–664 |doi=10.1111/j.1365-2389.1993.tb02330.x |access-date=25 April 2021}}</ref> |
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Soil atmosphere is also the seat of emissions of [[volatiles]] other than carbon and nitrogen oxides from various soil organisms, e.g. roots,<ref>{{cite journal |last1=Hiltpold |first1=Ivan |last2=Toepfer |first2=Stefan |last3=Kuhlmann |first3=Ulrich |last4=Turlings |first4=Ted C.J. |journal=Chemoecology |volume=20 |issue=2 |title=How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm? |url=https://www.researchgate.net/publication/215470509 |year=2010 |pages=155–162 |doi=10.1007/s00049-009-0034-6 |s2cid=30214059 |access-date=2 May 2021}}</ref> bacteria,<ref>{{cite journal |last1=Ryu |first1=Choong-Min |last2=Farag |first2=Mohamed A. |last3=Hu |first3=Chia-Hui |last4=Reddy |first4=Munagala S. |last5= Wei |first5= Han-Xun |last6= Paré |first6=Paul W. |last7= Kloepper |first7= Joseph W. |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=100 |issue=8 |title=Bacterial volatiles promote growth in Arabidopsis |url=https://www.pnas.org/content/pnas/100/8/4927.full.pdf |year=2003 |pages=4927–4932 |doi=10.1073/pnas.0730845100 |pmid=12684534 |pmc=153657 |access-date=2 May 2021 |bibcode=2003PNAS..100.4927R|doi-access=free }}</ref> fungi,<ref>{{cite journal |last1=Hung |first1=Richard |last2=Lee |first2=Samantha |last3=Bennett |first3=Joan W. |journal=[[Applied Microbiology and Biotechnology]] |volume=99 |issue=8 |title=Fungal volatile organic compounds and their role in ecosystems |url=https://www.researchgate.net/publication/273638498 |year=2015 |pages=3395–3405 |doi=10.1007/s00253-015-6494-4 |pmid=25773975 |s2cid=14509047 |access-date=2 May 2021}}</ref> animals.<ref>{{cite journal |last1=Purrington |first1=Foster Forbes |last2=Kendall |first2=Paricia A. |last3=Bater |first3=John E. |last4=Stinner |first4=Benjamin R. |journal=Great Lakes Entomologist |volume=24 |issue=2 |title=Alarm pheromone in a gregarious poduromorph collembolan (Collembola: Hypogastruridae) |url=https://scholar.valpo.edu/cgi/viewcontent.cgi?article=1732&context=tgle |year=1991 |pages=75–78 |access-date=2 May 2021}}</ref> These volatiles are used as chemical cues, making soil atmosphere the seat of interaction networks<ref>{{cite journal |last1=Badri |first1=Dayakar V. |last2=Weir |first2=Tiffany L. |last3=Van der Lelie |first3= Daniel |last4=Vivanco |first4=Jorge M |journal=[[Current Opinion in Biotechnology]] |volume=20 |issue=6 |title=Rhizosphere chemical dialogues: plant–microbe interactions |url=http://www.bicga.org.uk/docs/Rhizosphere_chemical_dialogues_plant.pdf |doi=10.1016/j.copbio.2009.09.014 |pmid=19875278 |year=2009 |pages=642–650}}</ref><ref>{{cite journal |last1=Salmon |first1=Sandrine |last2=Ponge |first2=Jean-François |journal=[[Soil Biology and Biochemistry]] |volume=33 |issue=14 |title=Earthworm excreta attract soil springtails: laboratory experiments on Heteromurus nitidus (Collembola: Entomobryidae) |url=https://www.academia.edu/20508985 |doi=10.1016/S0038-0717(01)00129-8 |year=2001 |pages=1959–1969 |access-date=2 May 2021}}</ref> playing a decisive role in the stability, dynamics and evolution of soil ecosystems.<ref>{{cite journal |last1=Lambers |first1=Hans |last2=Mougel |first2=Christophe |last3=Jaillard |first3=Benoît |last4=Hinsinger |first4=Philipe |journal=[[Plant and Soil]] |volume=321 |issue=1–2 |title=Plant-microbe-soil interactions in the rhizosphere: an evolutionary perspective |url=https://www.academia.edu/25517742 |doi=10.1007/s11104-009-0042-x |year=2009 |pages=83–115 |s2cid=6840457 |access-date=2 May 2021}}</ref> [[Biogenic substance|Biogenic]] soil volatile organic compounds are exchanged with the aboveground atmosphere, in which they are just 1–2 orders of magnitude lower than those from aboveground vegetation.<ref>{{cite journal |last1=Peñuelas |first1=Josep |last2=Asensio |first2=Dolores |last3=Tholl |first3=Dorothea |last4=Wenke |first4=Katrin |last5=Rosenkranz |first5=Maaria |last6=Piechulla |first6=Birgit |last7=Schnitzler |first7=Jörg-Petter |journal=[[Plant, Cell and Environment]] |volume=37 |issue=8 |title=Biogenic volatile emissions from the soil |year=2014 |pages=1866–1891 |doi=10.1111/pce.12340 |pmid=24689847 |doi-access=free}}</ref> |
Soil atmosphere is also the seat of emissions of [[volatiles]] other than carbon and nitrogen oxides from various soil organisms, e.g. roots,<ref>{{cite journal |last1=Hiltpold |first1=Ivan |last2=Toepfer |first2=Stefan |last3=Kuhlmann |first3=Ulrich |last4=Turlings |first4=Ted C.J. |journal=Chemoecology |volume=20 |issue=2 |title=How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm? |url=https://www.researchgate.net/publication/215470509 |year=2010 |pages=155–162 |doi=10.1007/s00049-009-0034-6 |s2cid=30214059 |access-date=2 May 2021}}</ref> bacteria,<ref>{{cite journal |last1=Ryu |first1=Choong-Min |last2=Farag |first2=Mohamed A. |last3=Hu |first3=Chia-Hui |last4=Reddy |first4=Munagala S. |last5= Wei |first5= Han-Xun |last6= Paré |first6=Paul W. |last7= Kloepper |first7= Joseph W. |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=100 |issue=8 |title=Bacterial volatiles promote growth in Arabidopsis |url=https://www.pnas.org/content/pnas/100/8/4927.full.pdf |year=2003 |pages=4927–4932 |doi=10.1073/pnas.0730845100 |pmid=12684534 |pmc=153657 |access-date=2 May 2021 |bibcode=2003PNAS..100.4927R|doi-access=free }}</ref> fungi,<ref>{{cite journal |last1=Hung |first1=Richard |last2=Lee |first2=Samantha |last3=Bennett |first3=Joan W. |journal=[[Applied Microbiology and Biotechnology]] |volume=99 |issue=8 |title=Fungal volatile organic compounds and their role in ecosystems |url=https://www.researchgate.net/publication/273638498 |year=2015 |pages=3395–3405 |doi=10.1007/s00253-015-6494-4 |pmid=25773975 |s2cid=14509047 |access-date=2 May 2021}}</ref> animals.<ref>{{cite journal |last1=Purrington |first1=Foster Forbes |last2=Kendall |first2=Paricia A. |last3=Bater |first3=John E. |last4=Stinner |first4=Benjamin R. |journal=Great Lakes Entomologist |volume=24 |issue=2 |title=Alarm pheromone in a gregarious poduromorph collembolan (Collembola: Hypogastruridae) |url=https://scholar.valpo.edu/cgi/viewcontent.cgi?article=1732&context=tgle |year=1991 |pages=75–78 |access-date=2 May 2021}}</ref> These volatiles are used as chemical cues, making soil atmosphere the seat of interaction networks<ref>{{cite journal |last1=Badri |first1=Dayakar V. |last2=Weir |first2=Tiffany L. |last3=Van der Lelie |first3= Daniel |last4=Vivanco |first4=Jorge M |journal=[[Current Opinion in Biotechnology]] |volume=20 |issue=6 |title=Rhizosphere chemical dialogues: plant–microbe interactions |url=http://www.bicga.org.uk/docs/Rhizosphere_chemical_dialogues_plant.pdf |doi=10.1016/j.copbio.2009.09.014 |pmid=19875278 |year=2009 |pages=642–650}}</ref><ref>{{cite journal |last1=Salmon |first1=Sandrine |last2=Ponge |first2=Jean-François |journal=[[Soil Biology and Biochemistry]] |volume=33 |issue=14 |title=Earthworm excreta attract soil springtails: laboratory experiments on Heteromurus nitidus (Collembola: Entomobryidae) |url=https://www.academia.edu/20508985 |doi=10.1016/S0038-0717(01)00129-8 |year=2001 |pages=1959–1969 |access-date=2 May 2021}}</ref> playing a decisive role in the stability, dynamics and evolution of soil ecosystems.<ref>{{cite journal |last1=Lambers |first1=Hans |last2=Mougel |first2=Christophe |last3=Jaillard |first3=Benoît |last4=Hinsinger |first4=Philipe |journal=[[Plant and Soil]] |volume=321 |issue=1–2 |title=Plant-microbe-soil interactions in the rhizosphere: an evolutionary perspective |url=https://www.academia.edu/25517742 |doi=10.1007/s11104-009-0042-x |year=2009 |pages=83–115 |s2cid=6840457 |access-date=2 May 2021}}</ref> [[Biogenic substance|Biogenic]] soil volatile organic compounds are exchanged with the aboveground atmosphere, in which they are just 1–2 orders of magnitude lower than those from aboveground vegetation.<ref>{{cite journal |last1=Peñuelas |first1=Josep |last2=Asensio |first2=Dolores |last3=Tholl |first3=Dorothea |last4=Wenke |first4=Katrin |last5=Rosenkranz |first5=Maaria |last6=Piechulla |first6=Birgit |last7=Schnitzler |first7=Jörg-Petter |journal=[[Plant, Cell and Environment]] |volume=37 |issue=8 |title=Biogenic volatile emissions from the soil |year=2014 |pages=1866–1891 |doi=10.1111/pce.12340 |pmid=24689847 |doi-access=free}}</ref> |
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==Chemistry== |
==Chemistry== |
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{{for|the |
{{for|the academic discipline|Soil chemistry}} |
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The chemistry of a soil determines its ability to supply available [[Plant nutrition|plant nutrients]] and affects its physical properties and the health of its living population. In addition, a soil's chemistry also determines its [[corrosivity]], stability, and ability to [[Sorption|absorb]] [[pollutants]] and to filter water. It is the [[surface chemistry]] of mineral and organic [[colloids]] that determines soil's chemical properties.<ref>{{cite book|author1-link=Garrison Sposito |last=Sposito |first=Garrison |date=1984 |title=The surface chemistry of soils |publisher=[[Oxford University Press]] |location=New York, New York |url=https://epdf.pub/the-surface-chemistry-of-soils.html |access-date=2 May 2021}}</ref> A colloid is a small, insoluble particle ranging in size from 1 [[nanometer]] to 1 [[micrometre|micrometer]], thus small enough to remain suspended by [[Brownian motion]] in a fluid medium without settling.<ref>{{cite web |last=Wynot |first=Christopher |title=Theory of diffusion in colloidal suspensions |url=http://www.owlnet.rice.edu/~ceng402/proj02/cwynot/402project.htm |access-date=2 May 2021}}</ref> Most soils contain organic colloidal particles called humus as well as the inorganic colloidal particles of [[clays]]. The very high [[specific surface area]] of colloids and their net [[electrical charge]]s give soil its ability to hold and release [[ions]]. Negatively charged sites on colloids attract and release cations in what is referred to as [[cation exchange]]. [[Cation-exchange capacity]] |
The chemistry of a soil determines its ability to supply available [[Plant nutrition|plant nutrients]] and affects its physical properties and the health of its living population. In addition, a soil's chemistry also determines its [[corrosivity]], stability, and ability to [[Sorption|absorb]] [[pollutants]] and to filter water. It is the [[surface chemistry]] of mineral and organic [[colloids]] that determines soil's chemical properties.<ref>{{cite book|author1-link=Garrison Sposito |last=Sposito |first=Garrison |date=1984 |title=The surface chemistry of soils |publisher=[[Oxford University Press]] |location=New York, New York |url=https://epdf.pub/the-surface-chemistry-of-soils.html |access-date=2 May 2021}}</ref> A colloid is a small, insoluble particle ranging in size from 1 [[nanometer]] to 1 [[micrometre|micrometer]], thus small enough to remain suspended by [[Brownian motion]] in a fluid medium without settling.<ref>{{cite web |last=Wynot |first=Christopher |title=Theory of diffusion in colloidal suspensions |url=http://www.owlnet.rice.edu/~ceng402/proj02/cwynot/402project.htm |access-date=2 May 2021}}</ref> Most soils contain organic colloidal particles called humus as well as the inorganic colloidal particles of [[clays]]. The very high [[specific surface area]] of colloids and their net [[electrical charge]]s give soil its ability to hold and release [[ions]]. Negatively charged sites on colloids attract and release cations in what is referred to as [[cation exchange]]. [[Cation-exchange capacity]] is the amount of exchangeable [[cations]] per unit weight of dry soil and is expressed in terms of [[milliequivalents]] of [[positively charged]] ions per 100 grams of soil (or centimoles of positive charge per kilogram of soil; cmol<sub>c</sub>/kg). Similarly, positively charged sites on colloids can attract and release [[anions]] in the soil, giving the soil anion exchange capacity. |
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===Cation and anion exchange=== |
===Cation and anion exchange=== |
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====Cation exchange capacity (CEC)==== |
====Cation exchange capacity (CEC)==== |
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[[Cation exchange capacity]] |
[[Cation exchange capacity]] is the soil's ability to remove cations from the soil water solution and sequester those to be exchanged later as the plant roots release hydrogen ions to the solution.<ref>{{cite journal |last=Brown |first=John C. |year=1978 |title=Mechanism of iron uptake by plants |journal=[[Plant, Cell & Environment|Plant, Cell and Environment]] |volume=1 |issue=4 |pages=249–257 |doi=10.1111/j.1365-3040.1978.tb02037.x |doi-access=free }}</ref> CEC is the amount of exchangeable hydrogen cation (H<sup>+</sup>) that will combine with 100 grams dry weight of soil and whose measure is one milliequivalents per 100 grams of soil (1 meq/100 g). Hydrogen ions have a single charge and one-thousandth of a gram of hydrogen ions per 100 grams dry soil gives a measure of one milliequivalent of hydrogen ion. Calcium, with an atomic weight 40 times that of hydrogen and with a valence of two, converts to {{nowrap|(40 ÷ 2) × 1 milliequivalent}} = 20 milliequivalents of hydrogen ion per 100 grams of dry soil or 20 meq/100 g.{{sfn|Donahue|Miller|Shickluna|1977|p=114}} The modern measure of CEC is expressed as centimoles of positive charge per kilogram (cmol/kg) of oven-dry soil. |
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Most of the soil's CEC occurs on clay and humus colloids, and the lack of those in hot, humid, wet climates (e.g. [[tropical rainforest]]s), due to leaching and decomposition, respectively, explains the apparent sterility of tropical soils.<ref>{{cite journal |last1=Singh |first1=Jamuna Sharan |last2=Raghubanshi |first2=Akhilesh Singh |last3=Singh |first3=Raj S. |last4=Srivastava |first4=S. C. |year=1989 |title=Microbial biomass acts as a source of plant nutrient in dry tropical forest and savanna |journal=[[Nature (journal)|Nature]] |volume=338 |issue=6215 |pages=499–500 |url=https://www.researchgate.net/publication/236941524 |doi=10.1038/338499a0 |access-date=23 May 2021 |bibcode=1989Natur.338..499S |s2cid=4301023 }}</ref> Live plant roots also have some CEC, linked to their specific surface area.<ref>{{cite journal |last1=Szatanik-Kloc |first1=Alicja |last2=Szerement |first2=Justyna |last3=Józefaciuk |first3=Grzegorz |year=2017 |title=The role of cell walls and pectins in cation exchange and surface area of plant roots |journal=[[Journal of Plant Physiology]] |volume=215 |pages=85–90 |url=https://www.researchgate.net/publication/317297194 |doi=10.1016/j.jplph.2017.05.017 |pmid=28600926 |access-date=23 May 2021 }}</ref> |
Most of the soil's CEC occurs on clay and humus colloids, and the lack of those in hot, humid, wet climates (e.g. [[tropical rainforest]]s), due to leaching and decomposition, respectively, explains the apparent sterility of tropical soils.<ref>{{cite journal |last1=Singh |first1=Jamuna Sharan |last2=Raghubanshi |first2=Akhilesh Singh |last3=Singh |first3=Raj S. |last4=Srivastava |first4=S. C. |year=1989 |title=Microbial biomass acts as a source of plant nutrient in dry tropical forest and savanna |journal=[[Nature (journal)|Nature]] |volume=338 |issue=6215 |pages=499–500 |url=https://www.researchgate.net/publication/236941524 |doi=10.1038/338499a0 |access-date=23 May 2021 |bibcode=1989Natur.338..499S |s2cid=4301023 }}</ref> Live plant roots also have some CEC, linked to their specific surface area.<ref>{{cite journal |last1=Szatanik-Kloc |first1=Alicja |last2=Szerement |first2=Justyna |last3=Józefaciuk |first3=Grzegorz |year=2017 |title=The role of cell walls and pectins in cation exchange and surface area of plant roots |journal=[[Journal of Plant Physiology]] |volume=215 |pages=85–90 |url=https://www.researchgate.net/publication/317297194 |doi=10.1016/j.jplph.2017.05.017 |pmid=28600926 |access-date=23 May 2021 }}</ref> |
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====Anion exchange capacity (AEC)==== |
====Anion exchange capacity (AEC)==== |
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Anion exchange capacity |
Anion exchange capacity is the soil's ability to remove anions (e.g. [[nitrate]], [[phosphate]]) from the soil water solution and sequester those for later exchange as the plant roots release carbonate anions to the soil water solution.<ref name="Hinsinger 2001 173–195">{{cite journal |last=Hinsinger |first=Philippe |year=2001 |title=Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review |journal=[[Plant and Soil]] |volume=237 |issue=2 |pages=173–195 |doi=10.1023/A:1013351617532 |doi-access=free }}</ref> Those colloids which have low CEC tend to have some AEC. Amorphous and sesquioxide clays have the highest AEC,<ref>{{cite journal |last1=Gu |first1=Baohua |last2=Schulz |first2=Robert K. |title=Anion retention in soil: possible application to reduce migration of buried technetium and iodine, a review |year=1991 |doi=10.2172/5980032 |doi-access=free }}</ref> followed by the iron oxides.<ref>{{cite journal |last1=Lawrinenko |first1=Michael |last2=Jing |first2=Dapeng |last3=Banik |first3=Chumki |last4=Laird |first4=David A. |year=2017 |title=Aluminum and iron biomass pretreatment impacts on biochar anion exchange capacity |journal=[[Carbon (journal)|Carbon]] |volume=118 |pages=422–430 |doi=10.1016/j.carbon.2017.03.056 |doi-access=free }}</ref> Levels of AEC are much lower than for CEC, because of the generally higher rate of positively (versus negatively) charged surfaces on soil colloids, to the exception of variable-charge soils.<ref>{{cite journal |last1=Sollins |first1=Phillip |last2=Robertson |first2=G. Philip |last3=Uehara |first3=Goro |year=1988 |title=Nutrient mobility in variable- and permanent-charge soils |journal=Biogeochemistry |volume=6 |issue=3 |pages=181–199 |url=https://lter.kbs.msu.edu/docs/robertson/Sollins_et_al._1988_Biogeochemistry.pdf |doi=10.1007/BF02182995 |s2cid=4505438 |doi-access=free }}</ref> Phosphates tend to be held at anion exchange sites.<ref>{{cite journal |last=Sanders |first=W. M. H. |year=1964 |title=Extraction of soil phosphate by anion-exchange membrane |journal=New Zealand Journal of Agricultural Research |volume=7 |issue=3 |pages=427–431 |doi=10.1080/00288233.1964.10416423 |doi-access=free }}</ref> |
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Iron and aluminum hydroxide clays are able to exchange their hydroxide anions (OH<sup>−</sup>) for other anions.<ref name="Hinsinger 2001 173–195"/> The order reflecting the strength of anion adhesion is as follows: |
Iron and aluminum hydroxide clays are able to exchange their hydroxide anions (OH<sup>−</sup>) for other anions.<ref name="Hinsinger 2001 173–195"/> The order reflecting the strength of anion adhesion is as follows: |
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There are acid-forming cations (e.g. hydronium, aluminium, iron) and there are base-forming cations (e.g. calcium, magnesium, sodium). The fraction of the negatively-charged soil colloid exchange sites (CEC) that are occupied by base-forming cations is called [[base saturation]]. If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations (acid-forming), the remainder of positions on the colloids ({{nowrap|1=20 − 5 = 15 meq}}) are assumed occupied by base-forming cations, so that the base saturation is {{nowrap|1=15 ÷ 20 × 100% = 75%}} (the compliment 25% is assumed acid-forming cations). Base saturation is almost in direct proportion to pH (it increases with increasing pH).<ref>{{cite journal |last1=McFee |first1=William W. |last2=Kelly |first2=J. Michael |last3=Beck |first3=Robert H. |year=1977 |title=Acid precipitation effects on soil pH and base saturation of exchange sites |journal=[[Water, Air, & Soil Pollution|Water, Air, and Soil Pollution]] |volume=7 |issue=3 |pages=4014–08 |doi=10.1007/BF00284134 |bibcode=1977WASP....7..401M |doi-access=free }}</ref> It is of use in calculating the amount of lime needed to neutralise an acid soil (lime requirement). The amount of lime needed to neutralize a soil must take account of the amount of acid forming ions on the colloids (exchangeable acidity), not just those in the soil water solution (free acidity).<ref>{{cite journal |last1=Farina |first1=Martin Patrick W. |last2=Sumner |first2=Malcolm E. |last3=Plank |first3=C. Owen |last4=Letzsch |first4=W. Stephen |year=1980 |title=Exchangeable aluminum and pH as indicators of lime requirement for corn |journal=[[Soil Science Society of America Journal]] |volume=44 |issue=5 |pages=1036–1041 |url=https://www.researchgate.net/publication/250123873 |access-date=20 June 2021 |doi=10.2136/sssaj1980.03615995004400050033x |bibcode=1980SSASJ..44.1036F }}</ref> The addition of enough lime to neutralize the soil water solution will be insufficient to change the pH, as the acid forming cations stored on the soil colloids will tend to restore the original pH condition as they are pushed off those colloids by the calcium of the added lime.{{sfn|Donahue|Miller|Shickluna|1977|pp=119–120}} |
There are acid-forming cations (e.g. hydronium, aluminium, iron) and there are base-forming cations (e.g. calcium, magnesium, sodium). The fraction of the negatively-charged soil colloid exchange sites (CEC) that are occupied by base-forming cations is called [[base saturation]]. If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations (acid-forming), the remainder of positions on the colloids ({{nowrap|1=20 − 5 = 15 meq}}) are assumed occupied by base-forming cations, so that the base saturation is {{nowrap|1=15 ÷ 20 × 100% = 75%}} (the compliment 25% is assumed acid-forming cations). Base saturation is almost in direct proportion to pH (it increases with increasing pH).<ref>{{cite journal |last1=McFee |first1=William W. |last2=Kelly |first2=J. Michael |last3=Beck |first3=Robert H. |year=1977 |title=Acid precipitation effects on soil pH and base saturation of exchange sites |journal=[[Water, Air, & Soil Pollution|Water, Air, and Soil Pollution]] |volume=7 |issue=3 |pages=4014–08 |doi=10.1007/BF00284134 |bibcode=1977WASP....7..401M |doi-access=free }}</ref> It is of use in calculating the amount of lime needed to neutralise an acid soil (lime requirement). The amount of lime needed to neutralize a soil must take account of the amount of acid forming ions on the colloids (exchangeable acidity), not just those in the soil water solution (free acidity).<ref>{{cite journal |last1=Farina |first1=Martin Patrick W. |last2=Sumner |first2=Malcolm E. |last3=Plank |first3=C. Owen |last4=Letzsch |first4=W. Stephen |year=1980 |title=Exchangeable aluminum and pH as indicators of lime requirement for corn |journal=[[Soil Science Society of America Journal]] |volume=44 |issue=5 |pages=1036–1041 |url=https://www.researchgate.net/publication/250123873 |access-date=20 June 2021 |doi=10.2136/sssaj1980.03615995004400050033x |bibcode=1980SSASJ..44.1036F }}</ref> The addition of enough lime to neutralize the soil water solution will be insufficient to change the pH, as the acid forming cations stored on the soil colloids will tend to restore the original pH condition as they are pushed off those colloids by the calcium of the added lime.{{sfn|Donahue|Miller|Shickluna|1977|pp=119–120}} |
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===Buffering=== |
====Buffering==== |
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{{Further|Soil conditioner}} |
{{Further|Soil conditioner}} |
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The resistance of soil to change in pH, as a result of the addition of acid or basic material, is a measure of the buffering capacity of a soil and (for a particular soil type) increases as the CEC increases. Hence, pure sand has almost no buffering ability, |
The resistance of soil to change in pH, as a result of the addition of acid or basic material, is a measure of the buffering capacity of a soil and (for a particular soil type) increases as the CEC increases. Hence, pure sand has almost no buffering ability, though soils high in colloids (whether mineral or organic) have high [[buffering capacity]].<ref>{{cite journal |last1=Sposito |first1=Garrison |last2=Skipper |first2=Neal T. |last3=Sutton |first3=Rebecca |last4=Park |first4=Sun-Ho |last5=Soper |first5=Alan K. |last6=Greathouse |first6=Jeffery A. |year=1999 |title=Surface geochemistry of the clay minerals |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=96 |issue=7 |pages=3358–3364 |doi=10.1073/pnas.96.7.3358 |pmid=10097044 |pmc=34275 |bibcode=1999PNAS...96.3358S |doi-access=free }}</ref> Buffering occurs by cation exchange and [[Neutralization (chemistry)|neutralisation]]. However, colloids are not the only regulators of soil pH. The role of [[carbonates]] should be underlined, too.<ref>{{cite web |last=Sparks |first=Donald L. |title=Acidic and basic soils: buffering |url=https://lawr.ucdavis.edu/classes/ssc102/Section8.pdf |publisher=[[University of California, Davis]], Department of Land, Air, and Water Resources |location=Davis, California |access-date=20 June 2021 }}</ref> More generally, according to pH levels, several buffer systems take precedence over each other, from [[calcium carbonate]] [[buffer range]] to iron buffer range.<ref>{{cite book |last=Ulrich |first=Bernhard |date=1983 |chapter=Soil acidity and its relations to acid deposition |title=Effects of accumulation of air pollutants in forest ecosystems |chapter-url=https://rd.springer.com/content/pdf/10.1007%2F978-94-009-6983-4_10.pdf |pages=127–146 |edition=1st |editor-last1=Ulrich |editor-first1=Bernhard |editor-last2=Pankrath |editor-first2=Jürgen |publisher=[[D. Reidel Publishing Company]] |location=Dordrecht, The Netherlands |isbn=978-94-009-6985-8 |doi=10.1007/978-94-009-6983-4_10 |access-date=21 June 2021 }}</ref> |
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The addition of a small amount of highly basic aqueous ammonia to a soil will cause the [[ammonium]] to displace hydronium ions from the colloids, and the end product is water and colloidally fixed ammonium, but little permanent change overall in soil pH. |
The addition of a small amount of highly basic aqueous ammonia to a soil will cause the [[ammonium]] to displace hydronium ions from the colloids, and the end product is water and colloidally fixed ammonium, but little permanent change overall in soil pH. |
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The above are examples of the buffering of soil pH. The general principal is that an increase in a particular cation in the soil water solution will cause that cation to be fixed to colloids (buffered) and a decrease in solution of that cation will cause it to be withdrawn from the colloid and moved into solution (buffered). The degree of buffering is often related to the CEC of the soil; the greater the CEC, the greater the buffering capacity of the soil.{{sfn|Donahue|Miller|Shickluna|1977|pp=120–121}} |
The above are examples of the buffering of soil pH. The general principal is that an increase in a particular cation in the soil water solution will cause that cation to be fixed to colloids (buffered) and a decrease in solution of that cation will cause it to be withdrawn from the colloid and moved into solution (buffered). The degree of buffering is often related to the CEC of the soil; the greater the CEC, the greater the buffering capacity of the soil.{{sfn|Donahue|Miller|Shickluna|1977|pp=120–121}} |
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===Redox=== |
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{{main|Redox#Redox_reactions_in_soils}} |
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{{See also|Table of standard reduction potentials for half-reactions important in biochemistry}} |
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Soil chemical reactions involve some combination of proton and electron transfer. Oxidation occurs if there is a loss of electrons in the transfer process while reduction occurs if there is a gain of electrons. [[Reduction potential]] is measured in volts or millivolts. Soil microbial communities develop along [[electron transport chain]]s, forming electrically conductive [[Geobacter#Biofilm_conductivity|biofilms]], and developing networks of [[bacterial nanowires]]. |
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Redox factors in soil development, where formation of [[redoximorphic features|redoximorphic color features]] provides critical information for soil interpretation. Understanding the [[Redox_gradient#Terrestrial_Environments|redox gradient]] is important to managing carbon sequestration, bioremediation, [[Pedosphere#Redox_conditions_in_wetland_soils|wetland delineation]], and [[soil-based microbial fuel cell]]s. |
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==Nutrients== |
==Nutrients== |
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==Soil organic matter== |
==Soil organic matter== |
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{{main|Soil organic matter}}{{Overly detailed|section|details=details could be moved into main article|date=April 2021}} |
{{main|Soil organic matter}}{{Overly detailed|section|details=details could be moved into main article|date=April 2021}} |
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The organic material in soil is made up of [[organic compounds]] and includes plant, animal and microbial material, both living and dead. A typical soil has a biomass composition of 70% microorganisms, 22% macrofauna, and 8% roots. The living component of an acre of soil may include 900 lb of earthworms, 2400 lb of fungi, 1500 lb of bacteria, 133 lb of protozoa and 890 lb of arthropods and algae.<ref>{{cite journal |last1=Pimentel |first1=David |last2=Harvey |first2=Celia |last3=Resosudarmo |first3=Pradnja |last4=Sinclair |first4=K. |last5=Kurz |first5=D. |last6=McNair |first6=M. |last7=Crist |first7=S. |last8=Shpritz |first8=L. |last9=Fitton |first9=L. |last10=Saffouri |first10=R. |last11=Blair |first11=R. |year=1995 |title=Environmental and economic costs 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 |pmid=17789193 |bibcode=1995Sci...267.1117P |s2cid=11936877 |access-date=4 July 2021 |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> |
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A few percent of the soil organic matter, with small [[residence time]], consists of the microbial [[biomass]] and [[metabolites]] of bacteria, molds, and actinomycetes that work to break down the dead organic matter.<ref>{{cite journal |last1=Schnürer |first1=Johan |last2=Clarholm |first2=Marianne |last3=Rosswall |first3=Thomas |year=1985 |title=Microbial biomass and activity in an agricultural soil with different organic matter contents |journal=[[Soil Biology and Biochemistry]] |volume=17 |issue=5 |pages=611–618 |url=https://www.academia.edu/20647751 |doi=10.1016/0038-0717(85)90036-7 |access-date=4 July 2021 }}</ref><ref>{{cite journal |last=Sparling |first=Graham P. |year=1992 |title=Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter |journal=[[Australian Journal of Soil Research]] |volume=30 |issue=2 |pages=195–207 |url=https://www.researchgate.net/publication/248884528 |doi=10.1071/SR9920195 |access-date=4 July 2021 }}</ref> Were it not for the action of these micro-organisms, the entire carbon dioxide part of the atmosphere would be sequestered as organic matter in the soil. However, in the same time soil microbes contribute to [[carbon sequestration]] in the topsoil through the formation of stable humus.<ref>{{cite journal |last1=Varadachari |first1=Chandrika |last2=Ghosh |first2=Kunal |year=1984 |title=On humus formation |journal=[[Plant and Soil]] |volume=77 |issue=2 |pages=305–313 |doi=10.1007/BF02182933 |s2cid=45102095 |doi-access=free }}</ref> In the aim to sequester more carbon in the soil for alleviating the [[greenhouse effect]] it would be more efficient in the long-term to stimulate [[humification]] than to decrease litter [[decomposition]].<ref>{{cite journal |last=Prescott |first=Cindy E. |year=2010 |title=Litter decomposition: what controls it and how can we alter it to sequester more carbon in forest soils? |journal=Biogeochemistry |volume=101 |issue=1 |pages=133–q49 |doi=10.1007/s10533-010-9439-0 |s2cid=93834812 |doi-access=free }}</ref> |
A few percent of the soil organic matter, with small [[residence time]], consists of the microbial [[biomass]] and [[metabolites]] of bacteria, molds, and actinomycetes that work to break down the dead organic matter.<ref>{{cite journal |last1=Schnürer |first1=Johan |last2=Clarholm |first2=Marianne |last3=Rosswall |first3=Thomas |year=1985 |title=Microbial biomass and activity in an agricultural soil with different organic matter contents |journal=[[Soil Biology and Biochemistry]] |volume=17 |issue=5 |pages=611–618 |url=https://www.academia.edu/20647751 |doi=10.1016/0038-0717(85)90036-7 |access-date=4 July 2021 }}</ref><ref>{{cite journal |last=Sparling |first=Graham P. |year=1992 |title=Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter |journal=[[Australian Journal of Soil Research]] |volume=30 |issue=2 |pages=195–207 |url=https://www.researchgate.net/publication/248884528 |doi=10.1071/SR9920195 |access-date=4 July 2021 }}</ref> Were it not for the action of these micro-organisms, the entire carbon dioxide part of the atmosphere would be sequestered as organic matter in the soil. However, in the same time soil microbes contribute to [[carbon sequestration]] in the topsoil through the formation of stable humus.<ref>{{cite journal |last1=Varadachari |first1=Chandrika |last2=Ghosh |first2=Kunal |year=1984 |title=On humus formation |journal=[[Plant and Soil]] |volume=77 |issue=2 |pages=305–313 |doi=10.1007/BF02182933 |s2cid=45102095 |doi-access=free }}</ref> In the aim to sequester more carbon in the soil for alleviating the [[greenhouse effect]] it would be more efficient in the long-term to stimulate [[humification]] than to decrease litter [[decomposition]].<ref>{{cite journal |last=Prescott |first=Cindy E. |year=2010 |title=Litter decomposition: what controls it and how can we alter it to sequester more carbon in forest soils? |journal=Biogeochemistry |volume=101 |issue=1 |pages=133–q49 |doi=10.1007/s10533-010-9439-0 |s2cid=93834812 |doi-access=free }}</ref> |
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Humus refers to organic matter that has been decomposed by soil microflora and fauna to the point where it is resistant to further breakdown. Humus usually constitutes only five percent of the soil or less by volume, but it is an essential source of nutrients and adds important textural qualities crucial to [[soil health]] and plant growth.<ref>{{cite web |url=http://www.harvestgrow.com/.pdf%20web%20site/Humates%20General%20Info.pdf |last=Pettit |first=Robert E. |title=Organic matter, humus, humate, humic acid, fulvic acid and humin: their importance in soil fertility and plant health |access-date=11 July 2021}}</ref> Humus also feeds arthropods, [[Termite|termites]] and [[Earthworm|earthworms]] which further improve the soil.<ref>{{cite journal |last1=Ji |first1=Rong |last2=Kappler |first2=Andreas |last3=Brune |first3=Andreas |year=2000 |title=Transformation and mineralization of synthetic <sup>14</sup>C-labeled humic model compounds by soil-feeding termites |journal=[[Soil Biology and Biochemistry]] |volume=32 |issue=8–9 |pages=1281–1291 |doi=10.1016/S0038-0717(00)00046-8 |url=https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.476.9400&rep=rep1&type=pdf |citeseerx=10.1.1.476.9400 |access-date=11 July 2021 }}</ref> The end product, humus, is suspended in [[colloidal]] form in the soil solution and forms a [[weak acid]] that can attack silicate minerals by [[Chelation|chelating]] their iron and aluminum atoms.<ref>{{cite book |last1=Drever |first1=James I. |last2=Vance |first2=George F. |year=1994 |chapter=Role of soil organic acids in mineral weathering processes |doi=10.1007/978-3-642-78356-2_6 |title=Organic acids in geological processes |editor-last1=Pittman |editor-first1=Edward D. |editor-last2=Lewan |editor-first2=Michael D. |publisher=[[Springer Science+Business Media|Springer]] |location=Berlin, Germany |pages=138–161 |isbn=978-3-642-78356-2 |chapter-url=https://link.springer.com/content/pdf/10.1007%2F978-3-642-78356-2_6.pdf |access-date=11 July 2021 }}</ref> Humus has a high cation and anion exchange capacity that on a dry weight basis is many times greater than that of clay colloids. It also acts as a buffer, like clay, against changes in pH and soil moisture.<ref name="Piccolo1996">{{cite book |last=Piccolo |first=Alessandro |year=1996 |chapter=Humus and soil conservation |doi=10.1016/B978-044481516-3/50006-2 |title=Humic substances in terrestrial ecosystems |editor-first=Alessandro |editor-last=Piccolo |publisher= [[Elsevier]] |location=Amsterdam, The Netherlands |pages=225–264 |isbn=978-0-444-81516-3 |chapter-url=https://www.researchgate.net/publication/281451183 |access-date=11 July 2021 }}</ref> |
Humus refers to organic matter that has been decomposed by soil microflora and fauna to the point where it is resistant to further breakdown. Humus usually constitutes only five percent of the soil or less by volume, but it is an essential source of nutrients and adds important textural qualities crucial to [[soil health]] and plant growth.<ref>{{cite web |url=http://www.harvestgrow.com/.pdf%20web%20site/Humates%20General%20Info.pdf |last=Pettit |first=Robert E. |title=Organic matter, humus, humate, humic acid, fulvic acid and humin: their importance in soil fertility and plant health |access-date=11 July 2021}}</ref> Humus also feeds arthropods, [[Termite|termites]] and [[Earthworm|earthworms]] which further improve the soil.<ref>{{cite journal |last1=Ji |first1=Rong |last2=Kappler |first2=Andreas |last3=Brune |first3=Andreas |year=2000 |title=Transformation and mineralization of synthetic <sup>14</sup>C-labeled humic model compounds by soil-feeding termites |journal=[[Soil Biology and Biochemistry]] |volume=32 |issue=8–9 |pages=1281–1291 |doi=10.1016/S0038-0717(00)00046-8 |url=https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.476.9400&rep=rep1&type=pdf |citeseerx=10.1.1.476.9400 |access-date=11 July 2021 }}</ref> The end product, humus, is suspended in [[colloidal]] form in the soil solution and forms a [[weak acid]] that can attack silicate minerals by [[Chelation|chelating]] their iron and aluminum atoms.<ref>{{cite book |last1=Drever |first1=James I. |last2=Vance |first2=George F. |year=1994 |chapter=Role of soil organic acids in mineral weathering processes |doi=10.1007/978-3-642-78356-2_6 |title=Organic acids in geological processes |editor-last1=Pittman |editor-first1=Edward D. |editor-last2=Lewan |editor-first2=Michael D. |publisher=[[Springer Science+Business Media|Springer]] |location=Berlin, Germany |pages=138–161 |isbn=978-3-642-78356-2 |chapter-url=https://link.springer.com/content/pdf/10.1007%2F978-3-642-78356-2_6.pdf |access-date=11 July 2021 }}</ref> Humus has a high cation and anion exchange capacity that on a dry weight basis is many times greater than that of clay colloids. It also acts as a buffer, like clay, against changes in pH and soil moisture.<ref name="Piccolo1996">{{cite book |last=Piccolo |first=Alessandro |year=1996 |chapter=Humus and soil conservation |doi=10.1016/B978-044481516-3/50006-2 |title=Humic substances in terrestrial ecosystems |editor-first=Alessandro |editor-last=Piccolo |publisher= [[Elsevier]] |location=Amsterdam, The Netherlands |pages=225–264 |isbn=978-0-444-81516-3 |chapter-url=https://www.researchgate.net/publication/281451183 |access-date=11 July 2021 }}</ref> |
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[[Humic acid]]s and [[fulvic acid]]s, which begin as raw organic matter, are important constituents of humus. After the death of plants, animals, and microbes, microbes begin to feed on the residues through their production of extra-cellular soil enzymes, resulting finally in the formation of humus.<ref>{{cite journal |last1=Varadachari |first1=Chandrika |last2=Ghosh |first2=Kunal |year=1984 |title=On humus formation |journal=[[Plant and Soil]] |volume=77 |issue=2 |pages=305–313 |url=https://www.researchgate.net/publication/225528442 |doi=10.1007/BF02182933 |s2cid=45102095 |access-date=11 July 2021 }}</ref> As the residues break down, only molecules made of [[aliphatic compound|aliphatic]] and [[aromatic hydrocarbon|aromatic]] hydrocarbons, assembled and stabilized by oxygen and hydrogen bonds, remain in the form of complex molecular assemblages collectively called humus.<ref name="Piccolo2002"/> Humus is never pure in the soil, because it reacts with metals and clays to form complexes which further contribute to its stability and to soil structure.<ref name="Piccolo1996"/> |
[[Humic acid]]s and [[fulvic acid]]s, which begin as raw organic matter, are important constituents of humus. After the death of plants, animals, and microbes, microbes begin to feed on the residues through their production of extra-cellular soil enzymes, resulting finally in the formation of humus.<ref>{{cite journal |last1=Varadachari |first1=Chandrika |last2=Ghosh |first2=Kunal |year=1984 |title=On humus formation |journal=[[Plant and Soil]] |volume=77 |issue=2 |pages=305–313 |url=https://www.researchgate.net/publication/225528442 |doi=10.1007/BF02182933 |s2cid=45102095 |access-date=11 July 2021 }}</ref> As the residues break down, only molecules made of [[aliphatic compound|aliphatic]] and [[aromatic hydrocarbon|aromatic]] hydrocarbons, assembled and stabilized by oxygen and hydrogen bonds, remain in the form of complex molecular assemblages collectively called humus.<ref name="Piccolo2002"/> Humus is never pure in the soil, because it reacts with metals and clays to form complexes which further contribute to its stability and to soil structure.<ref name="Piccolo1996"/> Although the structure of humus has in itself few nutrients (with the exception of constitutive metals such as calcium, iron and aluminum) it is able to attract and link, by weak bonds, cation and anion nutrients that can further be released into the soil solution in response to selective root uptake and changes in soil pH, a process of paramount importance for the maintenance of fertility in tropical soils.<ref>{{cite journal |last1=Mendonça |first1=Eduardo S. |last2=Rowell |first2=David L. |year=1996 |title=Mineral and organic fractions of two oxisols and their influence on effective cation-exchange capacity |journal=[[Soil Science Society of America Journal]] |volume=60 |issue=6 |pages=1888–1892 |url=https://www.researchgate.net/publication/250128642 |doi=10.2136/sssaj1996.03615995006000060038x |bibcode=1996SSASJ..60.1888M |access-date=11 July 2021 }}</ref> |
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[[Lignin]] is resistant to breakdown and accumulates within the soil. It also reacts with [[proteins]],<ref>{{cite journal |last1=Heck |first1=Tobias |last2=Faccio |first2=Greta |last3=Richter |first3=Michael |last4=Thöny-Meyer |first4=Linda |year=2013 |title=Enzyme-catalyzed protein crosslinking |journal=[[Applied Microbiology and Biotechnology]] |volume=97 |issue=2 |pages=461–475 |url=https://www.researchgate.net/publication/233769618 |doi=10.1007/s00253-012-4569-z |pmid=23179622 |pmc=3546294 |access-date=11 July 2021 }}</ref> which further increases its resistance to decomposition, including enzymatic decomposition by microbes.<ref>{{cite journal |last1=Lynch |first1=D. L. |last2=Lynch |first2=C. C. |year=1958 |title=Resistance of protein–lignin complexes, lignins and humic acids to microbial attack |journal=[[Nature (journal)|Nature]] |volume=181 |issue=4621 |pages=1478–1479 |url=https://www.nature.com/articles/1811478a0.pdf |doi=10.1038/1811478a0 |pmid=13552710 |bibcode=1958Natur.181.1478L |s2cid=4193782 |access-date=11 July 2021 }}</ref> [[Fat]]s and [[wax]]es from plant matter have still more resistance to decomposition and persist in soils for thousand years, hence their use as tracers of past vegetation in buried soil layers.<ref>{{cite journal |last1=Dawson |first1=Lorna A. |last2=Hillier |first2=Stephen |year=2010 |title=Measurement of soil characteristics for forensic applications |journal=[[Surface and Interface Analysis]] |volume=42 |issue=5 |pages=363–377 |url=https://people.ok.ubc.ca/robrien/soil%20characteristics.pdf |doi=10.1002/sia.3315 |access-date=18 July 2021 }}</ref> Clay soils often have higher organic contents that persist longer than soils without clay as the organic molecules adhere to and are stabilised by the clay.<ref>{{cite journal |last1=Manjaiah |first1=K.M. |last2=Kumar |first2=Sarvendra |last3=Sachdev |first3=M. S. |last4=Sachdev |first4=P. |last5=Datta |first5=S. C. |year=2010 |title=Study of clay–organic complexes |journal=[[Current Science]] |volume=98 |issue=7 |pages=915–921 |url=https://www.researchgate.net/publication/228867334 |access-date=18 July 2021 }}</ref> Proteins normally decompose readily, to the exception of [[scleroproteins]], but when bound to clay particles they become more resistant to decomposition.<ref>{{cite journal |last=Theng |first=Benny K.G. |year=1982 |title=Clay-polymer interactions: summary and perspectives |journal=Clays and Clay Minerals |volume=30 |issue=1 |pages=1–10 |doi=10.1346/CCMN.1982.0300101 |url=https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.608.2942 |bibcode=1982CCM....30....1T |citeseerx=10.1.1.608.2942 |s2cid=98176725 |access-date=18 July 2021 }}</ref> As for other proteins clay particles absorb the enzymes exuded by microbes, decreasing [[enzyme activity]] while protecting [[extracellular enzymes]] from degradation.<ref>{{cite journal |last1=Tietjen |first1=Todd |last2=Wetzel |first2=Robert G. |year=2003 |title=Extracellular enzyme-clay mineral complexes: enzyme adsorption, alteration of enzyme activity, and protection from photodegradation |journal=Aquatic Ecology |volume=37 |issue=4 |pages=331–339 |doi=10.1023/B:AECO.0000007044.52801.6b |s2cid=6930871 |url=http://www.vliz.be/imisdocs/publications/54440.pdf |access-date=18 July 2021 }}</ref> The addition of organic matter to clay soils can render that organic matter and any added nutrients inaccessible to plants and microbes for many years |
[[Lignin]] is resistant to breakdown and accumulates within the soil. It also reacts with [[proteins]],<ref>{{cite journal |last1=Heck |first1=Tobias |last2=Faccio |first2=Greta |last3=Richter |first3=Michael |last4=Thöny-Meyer |first4=Linda |year=2013 |title=Enzyme-catalyzed protein crosslinking |journal=[[Applied Microbiology and Biotechnology]] |volume=97 |issue=2 |pages=461–475 |url=https://www.researchgate.net/publication/233769618 |doi=10.1007/s00253-012-4569-z |pmid=23179622 |pmc=3546294 |access-date=11 July 2021 }}</ref> which further increases its resistance to decomposition, including enzymatic decomposition by microbes.<ref>{{cite journal |last1=Lynch |first1=D. L. |last2=Lynch |first2=C. C. |year=1958 |title=Resistance of protein–lignin complexes, lignins and humic acids to microbial attack |journal=[[Nature (journal)|Nature]] |volume=181 |issue=4621 |pages=1478–1479 |url=https://www.nature.com/articles/1811478a0.pdf |doi=10.1038/1811478a0 |pmid=13552710 |bibcode=1958Natur.181.1478L |s2cid=4193782 |access-date=11 July 2021 }}</ref> [[Fat]]s and [[wax]]es from plant matter have still more resistance to decomposition and persist in soils for thousand years, hence their use as tracers of past vegetation in buried soil layers.<ref>{{cite journal |last1=Dawson |first1=Lorna A. |last2=Hillier |first2=Stephen |year=2010 |title=Measurement of soil characteristics for forensic applications |journal=[[Surface and Interface Analysis]] |volume=42 |issue=5 |pages=363–377 |url=https://people.ok.ubc.ca/robrien/soil%20characteristics.pdf |doi=10.1002/sia.3315 |access-date=18 July 2021 }}</ref> Clay soils often have higher organic contents that persist longer than soils without clay as the organic molecules adhere to and are stabilised by the clay.<ref>{{cite journal |last1=Manjaiah |first1=K.M. |last2=Kumar |first2=Sarvendra |last3=Sachdev |first3=M. S. |last4=Sachdev |first4=P. |last5=Datta |first5=S. C. |year=2010 |title=Study of clay–organic complexes |journal=[[Current Science]] |volume=98 |issue=7 |pages=915–921 |url=https://www.researchgate.net/publication/228867334 |access-date=18 July 2021 }}</ref> Proteins normally decompose readily, to the exception of [[scleroproteins]], but when bound to clay particles they become more resistant to decomposition.<ref>{{cite journal |last=Theng |first=Benny K.G. |year=1982 |title=Clay-polymer interactions: summary and perspectives |journal=Clays and Clay Minerals |volume=30 |issue=1 |pages=1–10 |doi=10.1346/CCMN.1982.0300101 |url=https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.608.2942 |bibcode=1982CCM....30....1T |citeseerx=10.1.1.608.2942 |s2cid=98176725 |access-date=18 July 2021 }}</ref> As for other proteins clay particles absorb the enzymes exuded by microbes, decreasing [[enzyme activity]] while protecting [[extracellular enzymes]] from degradation.<ref>{{cite journal |last1=Tietjen |first1=Todd |last2=Wetzel |first2=Robert G. |year=2003 |title=Extracellular enzyme-clay mineral complexes: enzyme adsorption, alteration of enzyme activity, and protection from photodegradation |journal=Aquatic Ecology |volume=37 |issue=4 |pages=331–339 |doi=10.1023/B:AECO.0000007044.52801.6b |s2cid=6930871 |url=http://www.vliz.be/imisdocs/publications/54440.pdf |access-date=18 July 2021 }}</ref> The addition of organic matter to clay soils can render that organic matter and any added nutrients inaccessible to plants and microbes for many years.<ref>{{cite journal |last1=Tahir |first1=Shermeen |last2=Marschner |first2=Petra |year=2017 |title=Clay addition to sandy soil: influence of clay type and size on nutrient availability in sandy soils amended with residues differing in C/N ratio |journal=Pedosphere |volume=27 |issue=2 |pages=293–305 |url=https://www.researchgate.net/publication/314221508 |doi=10.1016/S1002-0160(17)60317-5 |access-date=18 July 2021 }}</ref> A study showed increased soil fertility following the addition of mature compost to a clay soil.<ref>{{cite journal |last1=Melero |first1=Sebastiana |last2=Madejón |first2=Engracia |last3=Ruiz |first3=Juan Carlos |last4=Herencia |first4=Juan Francisco |year=2007 |title=Chemical and biochemical properties of a clay soil under dryland agriculture system as affected by organic fertilization |journal=European Journal of Agronomy |volume=26 |issue=3 |pages=327–334 |url=https://coek.info/pdf-chemical-and-biochemical-properties-of-a-clay-soil-under-dryland-agriculture-sys.html |doi=10.1016/j.eja.2006.11.004 |access-date=18 July 2021 }}</ref> High soil [[tannin]] content can cause nitrogen to be sequestered as resistant tannin-protein complexes.<ref>{{cite journal |last1=Joanisse |first1=Gilles D. |last2=Bradley |first2=Robert L. |last3=Preston |first3=Caroline M. |last4=Bending |first4=Gary D. |title=Sequestration of soil nitrogen as tannin–protein complexes may improve the competitive ability of sheep laurel (Kalmia angustifolia) relative to black spruce (Picea mariana) |journal=[[New Phytologist]] |year=2009 |volume=181 |pages=187–198 |doi=10.1111/j.1469-8137.2008.02622.x |issue=1 |pmid=18811620 |doi-access=free }}</ref><ref name=Fierer2001>{{cite journal |last1=Fierer |first1=Noah |last2=Schimel |first2=Joshua P. |last3=Cates |first3=Rex G. |last4=Zou |first4=Jiping |title=Influence of balsam poplar tannin fractions on carbon and nitrogen dynamics in Alaskan taiga floodplain soils |journal=[[Soil Biology and Biochemistry]] |year=2001 |volume=33 |pages=1827–1839 |doi=10.1016/S0038-0717(01)00111-0 |issue=12–13 |url=https://www.academia.edu/12814037 |access-date=18 July 2021 }}</ref> |
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Humus formation is a process dependent on the amount of plant material added each year and the type of base soil. Both are affected by climate and the type of organisms present.<ref name="Ponge2003"/> Soils with humus can vary in nitrogen content but typically have 3 to 6 percent nitrogen. Raw organic matter, as a reserve of nitrogen and phosphorus, is a vital component affecting [[Fertile soil|soil fertility]].<ref name="Foth1984"/> Humus also absorbs water, and expands and shrinks between dry and wet states to a higher extent than clay, increasing soil porosity.<ref>{{cite journal |last1=Peng |first1=Xinhua |last2=Horn |first2=Rainer |title=Anisotropic shrinkage and swelling of some organic and inorganic soils |journal=European Journal of Soil Science |year=2007 |volume=58 |issue=1 |pages=98–107 |doi=10.1111/j.1365-2389.2006.00808.x |doi-access=free }}</ref> Humus is less stable than the soil's mineral constituents, as it is reduced by microbial decomposition, and over time its concentration diminishes without the addition of new organic matter. However, humus in its most stable forms may persist over centuries if not millennia.<ref>{{cite journal |last1=Wang |first1=Yang |last2=Amundson |first2=Ronald |last3=Trumbmore |first3=Susan |title=Radiocarbon dating of soil organic matter |journal=[[Quaternary Research]] |year=1996 |volume=45 |issue=3 |pages=282–288 |doi=10.1006/qres.1996.0029 |bibcode=1996QuRes..45..282W |url=https://escholarship.org/content/qt6b14h4bv/qt6b14h4bv.pdf |access-date=18 July 2021 }}</ref> [[Charcoal]] is a source of highly stable humus, called [[black carbon]],<ref>{{cite journal |last1=Brodowski |first1=Sonja |last2=Amelung |first2=Wulf |last3=Haumaier |first3=Ludwig |last4=Zech |first4=Wolfgang |title=Black carbon contribution to stable humus in German arable soils |journal=Geoderma |year=2007 |volume=139 |issue=1–2 |pages=220–228 |doi=10.1016/j.geoderma.2007.02.004 |bibcode=2007Geode.139..220B |url=https://www.academia.edu/33858429 |access-date=18 July 2021 }}</ref> which had been used traditionally to improve the fertility of nutrient-poor tropical soils. This very ancient practice, as ascertained in the genesis of [[Amazonian dark earths]], has been renewed and became popular under the name of [[biochar]]. It has been suggested that biochar could be used to sequester more carbon in the fight against the greenhouse effect.<ref>{{cite journal |last1=Criscuoli |first1=Irene |last2=Alberti |first2=Giorgio |last3=Baronti |first3=Silvia |last4=Favilli |first4=Filippo |last5=Martinez |first5=Cristina |last6=Calzolari |first6=Costanza |last7=Pusceddu |first7=Emanuela |last8=Rumpel |first8=Cornelia |last9=Viola |first9=Roberto |last10=Miglietta |first10=Franco |title=Carbon sequestration and fertility after centennial time scale incorporation of charcoal into soil |journal=PLOS ONE |year=2014 |volume=9 |issue=3 |pages=e91114 |doi=10.1371/journal.pone.0091114 |pmc=3948733 |pmid=24614647|bibcode=2014PLoSO...991114C |doi-access=free }}</ref> |
Humus formation is a process dependent on the amount of plant material added each year and the type of base soil. Both are affected by climate and the type of organisms present.<ref name="Ponge2003"/> Soils with humus can vary in nitrogen content but typically have 3 to 6 percent nitrogen. Raw organic matter, as a reserve of nitrogen and phosphorus, is a vital component affecting [[Fertile soil|soil fertility]].<ref name="Foth1984"/> Humus also absorbs water, and expands and shrinks between dry and wet states to a higher extent than clay, increasing soil porosity.<ref>{{cite journal |last1=Peng |first1=Xinhua |last2=Horn |first2=Rainer |title=Anisotropic shrinkage and swelling of some organic and inorganic soils |journal=European Journal of Soil Science |year=2007 |volume=58 |issue=1 |pages=98–107 |doi=10.1111/j.1365-2389.2006.00808.x |doi-access=free }}</ref> Humus is less stable than the soil's mineral constituents, as it is reduced by microbial decomposition, and over time its concentration diminishes without the addition of new organic matter. However, humus in its most stable forms may persist over centuries if not millennia.<ref>{{cite journal |last1=Wang |first1=Yang |last2=Amundson |first2=Ronald |last3=Trumbmore |first3=Susan |title=Radiocarbon dating of soil organic matter |journal=[[Quaternary Research]] |year=1996 |volume=45 |issue=3 |pages=282–288 |doi=10.1006/qres.1996.0029 |bibcode=1996QuRes..45..282W |url=https://escholarship.org/content/qt6b14h4bv/qt6b14h4bv.pdf |access-date=18 July 2021 }}</ref> [[Charcoal]] is a source of highly stable humus, called [[black carbon]],<ref>{{cite journal |last1=Brodowski |first1=Sonja |last2=Amelung |first2=Wulf |last3=Haumaier |first3=Ludwig |last4=Zech |first4=Wolfgang |title=Black carbon contribution to stable humus in German arable soils |journal=Geoderma |year=2007 |volume=139 |issue=1–2 |pages=220–228 |doi=10.1016/j.geoderma.2007.02.004 |bibcode=2007Geode.139..220B |url=https://www.academia.edu/33858429 |access-date=18 July 2021 }}</ref> which had been used traditionally to improve the fertility of nutrient-poor tropical soils. This very ancient practice, as ascertained in the genesis of [[Amazonian dark earths]], has been renewed and became popular under the name of [[biochar]]. It has been suggested that biochar could be used to sequester more carbon in the fight against the greenhouse effect.<ref>{{cite journal |last1=Criscuoli |first1=Irene |last2=Alberti |first2=Giorgio |last3=Baronti |first3=Silvia |last4=Favilli |first4=Filippo |last5=Martinez |first5=Cristina |last6=Calzolari |first6=Costanza |last7=Pusceddu |first7=Emanuela |last8=Rumpel |first8=Cornelia |last9=Viola |first9=Roberto |last10=Miglietta |first10=Franco |title=Carbon sequestration and fertility after centennial time scale incorporation of charcoal into soil |journal=PLOS ONE |year=2014 |volume=9 |issue=3 |pages=e91114 |doi=10.1371/journal.pone.0091114 |pmc=3948733 |pmid=24614647|bibcode=2014PLoSO...991114C |doi-access=free }}</ref> |
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{{main|Soil classification}} |
{{main|Soil classification}} |
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One of the first soil classification systems was developed by Russian scientist [[Vasily Dokuchaev]] around 1880.<ref>{{cite web |url=https://fr.scribd.com/doc/206859253/Russian-Chernozem |title=Russian Chernozem |last=Dokuchaev |first=Vasily Vasilyevich |publisher=Israel Program for Scientific Translations |location=Jerusalem, Israel |year=1967 |access-date=15 August 2021 }}</ref> It was modified a number of times by American and European researchers and was developed into the system commonly used until the 1960s. It was based on the idea that soils have a particular morphology based on the materials and factors that form them. In the 1960s, a different classification system began to emerge which focused on [[soil morphology]] instead of parental materials and soil-forming factors. Since then, it has undergone further modifications. The [[World Reference Base for Soil Resources]]<ref name=IUSS2014>{{cite book |last=[[International Union of Soil Sciences|IUSS]] Working Group WRB |title=World Reference Base for Soil Resources 2014: international soil classification system for naming soils and creating legends for soil maps, update 2015 |year=2015 |publisher=[[Food and Agriculture Organization]] |location=Rome, Italy |isbn=978-92-5-108370-3 |url=http://www.fao.org/3/a-i3794en.pdf |access-date=15 August 2021 }}</ref> aims to establish an international reference base for soil classification. |
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==Uses== |
==Uses== |
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==Degradation== |
==Degradation== |
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{{Main|Soil retrogression and degradation|Soil conservation}} |
{{Main|Soil retrogression and degradation|Soil conservation}} |
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[[Land degradation]] |
[[Land degradation]] is a human-induced or natural process which impairs the capacity of [[land (economics)|land]] to function.<ref>{{cite journal |last1=Johnson |first1=Dan L. |last2=Ambrose |first2=Stanley H. |last3=Bassett |first3=Thomas J. |last4=Bowen | first4=Merle L. |last5=Crummey |first5=Donald E. |last6=Isaacson |first6=John S. |last7=Johnson |first7=David N. |last8=Lamb |first8=Peter |last9=Saul | first9=Mahir |last10=Winter-Nelson |first10=Alex E. |year=1997 |title=Meanings of environmental terms |url=https://www.researchgate.net/publication/240784159 |journal=[[Journal of Environmental Quality]] |volume=26 |issue=3 |pages=581–589 |doi=10.2134/jeq1997.00472425002600030002x |access-date=29 August 2021 }}</ref> Soil degradation involves [[Soil acidification|acidification]], [[soil contamination|contamination]], [[desertification]], [[erosion]] or [[Soil salinity|salination]].<ref>{{cite book |last=Oldeman |first=L. Roel |year=1993 |chapter=Global extent of soil degradation |title=ISRIC Bi-Annual Report 1991–1992 |pages=19–36 |chapter-url=https://library.wur.nl/WebQuery/wurpubs/fulltext/299739 |publisher=[[International Soil Reference and Information Centre]](ISRIC) |location=Wageningen, The Netherlands |access-date=29 August 2021 }}</ref> |
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=== Acidification === |
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Soil acidification is beneficial in the case of [[alkaline soil]]s, but it degrades land when it lowers [[crop productivity]], soil biological activity and increases soil vulnerability to [[contamination]] and erosion. Soils are initially acid and remain such when their parent materials are low in basic [[cation]]s (calcium, magnesium, potassium and [[sodium]]). On parent materials richer in [[mineral weathering|weatherable minerals]] acidification occurs when basic cations are [[Leaching (pedology)|leached]] from the soil profile by rainfall or exported by the harvesting of forest or agricultural crops. Soil acidification is accelerated by the use of acid-forming [[nitrogenous fertilizer]]s and by the effects of [[acid precipitation]]. [[Deforestation]] is another cause of soil acidification, mediated by increased leaching of soil nutrients in the absence of [[tree canopies]].<ref>{{cite book |last1=Sumner |first1=Malcolm E. |last2=Noble |first2=Andrew D. |year=2003 |chapter=Soil acidification: the world story |title=Handbook of soil acidity |pages=1–28 |editor-last=Rengel |editor-first=Zdenko |chapter-url=https://pdf-drive.com/pdf/Zdenko20Rengel20-20Handbook20of20Soil20Acidity2028Books20in20Soils2C20Plants2C20and20the20Environment292028200329.pdf#page=16 |publisher=[[Marcel Dekker]] |location=New York, NY, USA |access-date=29 August 2021 }}</ref> |
Soil acidification is beneficial in the case of [[alkaline soil]]s, but it degrades land when it lowers [[crop productivity]], soil biological activity and increases soil vulnerability to [[contamination]] and erosion. Soils are initially acid and remain such when their parent materials are low in basic [[cation]]s (calcium, magnesium, potassium and [[sodium]]). On parent materials richer in [[mineral weathering|weatherable minerals]] acidification occurs when basic cations are [[Leaching (pedology)|leached]] from the soil profile by rainfall or exported by the harvesting of forest or agricultural crops. Soil acidification is accelerated by the use of acid-forming [[nitrogenous fertilizer]]s and by the effects of [[acid precipitation]]. [[Deforestation]] is another cause of soil acidification, mediated by increased leaching of soil nutrients in the absence of [[tree canopies]].<ref>{{cite book |last1=Sumner |first1=Malcolm E. |last2=Noble |first2=Andrew D. |year=2003 |chapter=Soil acidification: the world story |title=Handbook of soil acidity |pages=1–28 |editor-last=Rengel |editor-first=Zdenko |chapter-url=https://pdf-drive.com/pdf/Zdenko20Rengel20-20Handbook20of20Soil20Acidity2028Books20in20Soils2C20Plants2C20and20the20Environment292028200329.pdf#page=16 |publisher=[[Marcel Dekker]] |location=New York, NY, USA |access-date=29 August 2021 }}</ref> |
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=== Contamination === |
=== Contamination === |
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Soil [[contamination]] at low levels is often within a soil's capacity to treat and assimilate [[waste]] material. [[Soil biota]] can treat waste by transforming it, mainly through microbial [[Enzyme|enzymatic]] activity.<ref>{{cite journal |last1=Karam |first1=Jean |last2=Nicell |first2=James A. |year=1997 |title=Potential applications of enzymes in waste treatment |url=https://www.researchgate.net/publication/30002097 |journal=[[Journal of Chemical Technology & Biotechnology]] |volume=69 |issue=2 |pages=141–153 |doi=10.1002/(SICI)1097-4660(199706)69:2<141::AID-JCTB694>3.0.CO;2-U |access-date=5 September 2021 }}</ref> Soil organic matter and soil minerals can adsorb the waste material and decrease its [[toxicity]],<ref>{{cite journal |last1=Sheng |first1=Guangyao |last2=Johnston |first2=Cliff T. |last3=Teppen |first3=Brian J. |last4=Boyd |first4=Stephen A. |year=2001 |title=Potential contributions of smectite clays and organic matter to pesticide retention in soils |url=https://www.academia.edu/4875079 |journal=[[Journal of Agricultural and Food Chemistry]] |volume=49 |issue=6 |pages=2899–2907 |doi=10.1021/jf001485d |pmid=11409985 |access-date=5 September 2021 }}</ref> although when in colloidal form they may transport the adsorbed contaminants to subsurface environments.<ref>{{cite journal |last1=Sprague |first1=Lori A. |last2=Herman |first2=Janet S. |last3=Hornberger |first3=George M. |last4=Mills | first4=Aaron L. |year=2000 |title=Atrazine adsorption and colloid‐facilitated transport through the unsaturated zone |url=https://lmecol.evsc.virginia.edu/pubs/73-Sprague_JEQ2000.pdf |journal=[[Journal of Environmental Quality]] |volume=29 |issue=5 |pages=1632–1641 |doi=10.2134/jeq2000.00472425002900050034x |access-date=5 September 2021 }}</ref> Many waste treatment processes rely on this natural [[bioremediation]] capacity. Exceeding treatment capacity can damage soil biota and limit soil function. Derelict soils occur where industrial contamination or other development activity damages the soil to such a degree that the land cannot be used safely or productively. [[Environmental remediation|Remediation]] of derelict soil uses principles of geology, physics, chemistry and biology to degrade, attenuate, isolate or remove soil contaminants to restore [[soil functions]] and values. Techniques include [[Leaching (chemistry)|leaching]], [[air sparging]], [[soil conditioner]]s, [[phytoremediation]], bioremediation and [[In situ bioremediation|Monitored Natural Attenuation |
Soil [[contamination]] at low levels is often within a soil's capacity to treat and assimilate [[waste]] material. [[Soil biota]] can treat waste by transforming it, mainly through microbial [[Enzyme|enzymatic]] activity.<ref>{{cite journal |last1=Karam |first1=Jean |last2=Nicell |first2=James A. |year=1997 |title=Potential applications of enzymes in waste treatment |url=https://www.researchgate.net/publication/30002097 |journal=[[Journal of Chemical Technology & Biotechnology]] |volume=69 |issue=2 |pages=141–153 |doi=10.1002/(SICI)1097-4660(199706)69:2<141::AID-JCTB694>3.0.CO;2-U |access-date=5 September 2021 }}</ref> Soil organic matter and soil minerals can adsorb the waste material and decrease its [[toxicity]],<ref>{{cite journal |last1=Sheng |first1=Guangyao |last2=Johnston |first2=Cliff T. |last3=Teppen |first3=Brian J. |last4=Boyd |first4=Stephen A. |year=2001 |title=Potential contributions of smectite clays and organic matter to pesticide retention in soils |url=https://www.academia.edu/4875079 |journal=[[Journal of Agricultural and Food Chemistry]] |volume=49 |issue=6 |pages=2899–2907 |doi=10.1021/jf001485d |pmid=11409985 |access-date=5 September 2021 }}</ref> although when in colloidal form they may transport the adsorbed contaminants to subsurface environments.<ref>{{cite journal |last1=Sprague |first1=Lori A. |last2=Herman |first2=Janet S. |last3=Hornberger |first3=George M. |last4=Mills | first4=Aaron L. |year=2000 |title=Atrazine adsorption and colloid‐facilitated transport through the unsaturated zone |url=https://lmecol.evsc.virginia.edu/pubs/73-Sprague_JEQ2000.pdf |journal=[[Journal of Environmental Quality]] |volume=29 |issue=5 |pages=1632–1641 |doi=10.2134/jeq2000.00472425002900050034x |access-date=5 September 2021 }}</ref> Many waste treatment processes rely on this natural [[bioremediation]] capacity. Exceeding treatment capacity can damage soil biota and limit soil function. Derelict soils occur where industrial contamination or other development activity damages the soil to such a degree that the land cannot be used safely or productively. [[Environmental remediation|Remediation]] of derelict soil uses principles of geology, physics, chemistry and biology to degrade, attenuate, isolate or remove soil contaminants to restore [[soil functions]] and values. Techniques include [[Leaching (chemistry)|leaching]], [[air sparging]], [[soil conditioner]]s, [[phytoremediation]], bioremediation and [[In situ bioremediation|Monitored Natural Attenuation]]. An example of diffuse pollution with contaminants is copper accumulation in [[vineyard]]s and [[orchard]]s to which fungicides are repeatedly applied, even in [[organic farming]].<ref>{{Cite journal |last1=Ballabio |first1=Cristiano |last2=Panagos |first2=Panos |last3=Lugato |first3=Emanuele |last4=Huang |first4=Jen-How |last5=Orgiazzi |first5=Alberto |last6=Jones |first6=Arwyn |last7=Fernández-Ugalde |first7=Oihane |last8=Borrelli |first8=Pasquale |last9=Montanarella |first9=Luca |date=15 September 2018 |title=Copper distribution in European topsoils: an assessment based on LUCAS soil survey |journal=[[Science of the Total Environment]] |volume=636 |pages=282–298 |doi=10.1016/j.scitotenv.2018.04.268 |pmid=29709848 |issn=0048-9697 |bibcode=2018ScTEn.636..282B |doi-access=free }}</ref> |
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Microfibres from synthetic textiles are another type of plastic soil contamination, 100% of agricultural soil samples from southwestern China contained plastic particles, 92% of which were microfibres. Sources of microfibres likely included string or twine, as well as irrigation water in which clothes had been washed.<ref>{{Cite web |last=Environment |first=U. N. |date=2021-10-21 |title=Drowning in Plastics – Marine Litter and Plastic Waste Vital Graphics |url=http://www.unep.org/resources/report/drowning-plastics-marine-litter-and-plastic-waste-vital-graphics |access-date=2022-03-23 |website=UNEP - UN Environment Programme |language=en}}</ref> |
Microfibres from synthetic textiles are another type of plastic soil contamination, 100% of agricultural soil samples from southwestern China contained plastic particles, 92% of which were microfibres. Sources of microfibres likely included string or twine, as well as irrigation water in which clothes had been washed.<ref>{{Cite web |last=Environment |first=U. N. |date=2021-10-21 |title=Drowning in Plastics – Marine Litter and Plastic Waste Vital Graphics |url=http://www.unep.org/resources/report/drowning-plastics-marine-litter-and-plastic-waste-vital-graphics |access-date=2022-03-23 |website=UNEP - UN Environment Programme |language=en}}</ref> |
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[[File:Soil erosion, Southfield - geograph.org.uk - 367917.jpg|thumb|Desertification]] |
[[File:Soil erosion, Southfield - geograph.org.uk - 367917.jpg|thumb|Desertification]] |
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[[Desertification]] |
[[Desertification]], an environmental process of ecosystem degradation in arid and semi-arid regions, is often caused by badly adapted human activities such as [[overgrazing]] or excess harvesting of [[firewood]]. It is a common misconception that [[drought]] causes desertification.<ref>{{Cite journal |last=Le Houérou |first=Henry N. |year=1996 |title=Climate change, drought and desertification |journal=[[Journal of Arid Environments]] |volume=34 |issue=2 |pages=133–185 |doi=10.1006/jare.1996.0099 |bibcode=1996JArEn..34..133L |url=http://www7.nau.edu/mpcer/direnet/publications/publications_l/files/LeHouerou_1996.pdf |access-date=5 September 2021 }}</ref> Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. [[Soil management]] tools include maintaining soil nutrient and organic matter levels, reduced tillage and increased cover.<ref>{{Cite journal |last1=Lyu |first1=Yanli |last2=Shi |first2=Peijun |last3=Han |first3=Guoyi |last4=Liu |first4=Lianyou |last5=Guo |first5=Lanlan |last6=Hu |first6=Xia |last7=Zhang |first7=Guoming |year=2020 |title=Desertification control practices in China |journal=Sustainability |volume=12 |issue=8 |pages=3258 |doi=10.3390/su12083258 |issn=2071-1050 |doi-access=free }}</ref> These practices help to control erosion and maintain productivity during periods when moisture is available. Continued land abuse during droughts, however, increases [[land degradation]]. Increased population and livestock pressure on marginal lands accelerates desertification.<ref>{{Cite journal |last1=Kéfi |first1=Sonia |last2=Rietkerk |first2=Max |last3=Alados |first3=Concepción L. |last4=Pueyo |first4=Yolanda |last5=Papanastasis |first5=Vasilios P. |last6=El Aich |first6=Ahmed |last7=de Ruiter |first7=Peter C. |year=2007 |title=Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems |journal=[[Nature (journal)|Nature]] |volume=449 |issue=7159 |pages=213–217 |doi=10.1038/nature06111 |pmid=17851524 |bibcode=2007Natur.449..213K |hdl=1874/25682 |s2cid=4411922 |url=https://www.researchgate.net/publication/232801317 |access-date=5 September 2021 }}</ref> It is now questioned whether present-day climate warming will favour or disfavour desertification, with contradictory reports about predicted rainfall trends associated with increased temperature, and strong discrepancies among regions, even in the same country.<ref>{{Cite journal |last1=Wang |first1=Xunming |last2=Yang |first2=Yi |last3=Dong |first3=Zhibao |last4=Zhang |first4=Caixia |year=2009 |title=Responses of dune activity and desertification in China to global warming in the twenty-first century |journal=[[Global and Planetary Change]] |volume=67 |issue=3–4 |pages=167–185 |doi=10.1016/j.gloplacha.2009.02.004 |bibcode=2009GPC....67..167W |url=https://www.researchgate.net/publication/229103975 |access-date=5 September 2021 }}</ref> |
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=== Erosion === |
=== Erosion === |
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[[File:Riparian buffer on Bear Creek in Story County, Iowa.JPG|thumb|upright|Erosion control]] |
[[File:Riparian buffer on Bear Creek in Story County, Iowa.JPG|thumb|upright|Erosion control]] |
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[[Erosion]] of soil is caused by [[Water erosion#Rainfall|water]], [[Water erosion#Wind erosion|wind]], [[Water erosion#Glaciers|ice]], and [[Water erosion#Mass movement|movement in response to gravity]]. More than one kind of erosion can occur simultaneously. Erosion is distinguished from [[weathering]], since erosion also transports eroded soil away from its place of origin (soil in transit may be described as [[sediment]]). Erosion is an intrinsic natural process, but in many places it is greatly increased by human activity, especially unsuitable land use practices.<ref>{{Cite journal |last1=Yang |first1=Dawen |last2=Kanae |first2=Shinjiro |last3=Oki |first3=Taikan |last4=Koike |first4=Toshio |last5=Musiake |first5=Katumi |year=2003 |title=Global potential soil erosion with reference to land use and climate changes |journal=Hydrological Processes |volume=17 |issue=14 |pages=2913–28 |doi=10.1002/hyp.1441 |bibcode=2003HyPr...17.2913Y |url=https://www.oieau.org/eaudoc/system/files/documents/38/191115/191115_doc.pdf |access-date=5 September 2021 }}</ref> These include [[agriculture|agricultural]] activities which leave the soil bare during times of heavy rain or strong winds, [[overgrazing]], [[deforestation]], and improper [[construction]] activity. Improved management can limit erosion. [[Soil conservation#Erosion prevention|Soil conservation techniques]] which are employed include changes of land use (such as replacing erosion-prone [[crop]]s with [[grass]] or other soil-binding plants), changes to the timing or type of agricultural operations, [[Terrace (agriculture)|terrace]] building, use of erosion-suppressing cover materials (including [[Cover crop#Water management|cover crops]] and |
[[Erosion]] of soil is caused by [[Water erosion#Rainfall|water]], [[Water erosion#Wind erosion|wind]], [[Water erosion#Glaciers|ice]], and [[Water erosion#Mass movement|movement in response to gravity]]. More than one kind of erosion can occur simultaneously. Erosion is distinguished from [[weathering]], since erosion also transports eroded soil away from its place of origin (soil in transit may be described as [[sediment]]). Erosion is an intrinsic natural process, but in many places it is greatly increased by human activity, especially unsuitable land use practices.<ref>{{Cite journal |last1=Yang |first1=Dawen |last2=Kanae |first2=Shinjiro |last3=Oki |first3=Taikan |last4=Koike |first4=Toshio |last5=Musiake |first5=Katumi |year=2003 |title=Global potential soil erosion with reference to land use and climate changes |journal=Hydrological Processes |volume=17 |issue=14 |pages=2913–28 |doi=10.1002/hyp.1441 |bibcode=2003HyPr...17.2913Y |url=https://www.oieau.org/eaudoc/system/files/documents/38/191115/191115_doc.pdf |access-date=5 September 2021 }}</ref> These include [[agriculture|agricultural]] activities which leave the soil bare during times of heavy rain or strong winds, [[overgrazing]], [[deforestation]], and improper [[construction]] activity. Improved management can limit erosion. [[Soil conservation#Erosion prevention|Soil conservation techniques]] which are employed include changes of land use (such as replacing erosion-prone [[crop]]s with [[grass]] or other soil-binding plants), changes to the timing or type of agricultural operations, [[Terrace (agriculture)|terrace]] building, use of erosion-suppressing cover materials (including [[Cover crop#Water management|cover crops]] and other plants), limiting disturbance during construction, and avoiding construction during erosion-prone periods and in erosion-prone places such as steep slopes.<ref>{{Cite journal |last1=Sheng |first1=Jian-an |last2=Liao |first2=An-zhong |year=1997 |title=Erosion control in South China |journal=Catena |issn=0341-8162 |volume=29 |issue=2 |pages=211–221 |doi=10.1016/S0341-8162(96)00057-4 |url=https://coek.info/pdf-erosion-control-in-south-china-.html |access-date=5 September 2021 }}</ref> Historically, one of the best examples of large-scale soil erosion due to unsuitable land-use practices is wind erosion (the so-called [[Dust Bowl|dust bowl]]) which ruined American and Canadian prairies during the 1930s, when immigrant farmers, encouraged by the federal government of both countries, settled and converted the original [[shortgrass prairie]] to [[agricultural crops]] and [[cattle ranching]]. |
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A serious and long-running water erosion problem occurs in [[China]], on the middle reaches of the [[Yellow River]] and the upper reaches of the [[Yangtze River]]. From the Yellow River, over 1.6 billion tons of sediment flow each year into the ocean. The sediment originates primarily from water erosion (gully erosion) in the [[Loess Plateau]] region of northwest China.<ref>{{Cite journal |last1=Ran |first1=Lishan |last2=Lu |first2=Xi Xi |last3=Xin |first3=Zhongbao |year=2014 |title=Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China |journal=[[Biogeosciences]] |volume=11 |issue=4 |pages=945–959 |doi=10.5194/bg-11-945-2014 |bibcode=2014BGeo...11..945R |url=https://bg.copernicus.org/articles/11/945/2014/bg-11-945-2014.pdf |access-date=5 September 2021 |hdl=10722/228184 |hdl-access=free }}</ref> |
A serious and long-running water erosion problem occurs in [[China]], on the middle reaches of the [[Yellow River]] and the upper reaches of the [[Yangtze River]]. From the Yellow River, over 1.6 billion tons of sediment flow each year into the ocean. The sediment originates primarily from water erosion (gully erosion) in the [[Loess Plateau]] region of northwest China.<ref>{{Cite journal |last1=Ran |first1=Lishan |last2=Lu |first2=Xi Xi |last3=Xin |first3=Zhongbao |year=2014 |title=Erosion-induced massive organic carbon burial and carbon emission in the Yellow River basin, China |journal=[[Biogeosciences]] |volume=11 |issue=4 |pages=945–959 |doi=10.5194/bg-11-945-2014 |bibcode=2014BGeo...11..945R |url=https://bg.copernicus.org/articles/11/945/2014/bg-11-945-2014.pdf |access-date=5 September 2021 |hdl=10722/228184 |hdl-access=free }}</ref> |
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==Reclamation== |
==Reclamation== |
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{{Main|Soil regeneration}} |
{{Main|Soil regeneration}} |
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Soils which contain high levels of particular clays with high swelling properties, such as [[smectite]]s, are often very fertile. For example, the smectite-rich [[Paddy field|paddy]] soils of Thailand's [[Central Thailand|Central Plains]] are among the most productive in the world. However, the overuse of mineral nitrogen [[fertilizer]]s and pesticides in [[Irrigation|irrigated]] intensive [[Rice production in Thailand|rice production]] has endangered these soils, forcing farmers to implement [[integrated farming|integrated practices]] based on Cost Reduction Operating Principles |
Soils which contain high levels of particular clays with high swelling properties, such as [[smectite]]s, are often very fertile. For example, the smectite-rich [[Paddy field|paddy]] soils of Thailand's [[Central Thailand|Central Plains]] are among the most productive in the world. However, the overuse of mineral nitrogen [[fertilizer]]s and pesticides in [[Irrigation|irrigated]] intensive [[Rice production in Thailand|rice production]] has endangered these soils, forcing farmers to implement [[integrated farming|integrated practices]] based on Cost Reduction Operating Principles.<ref>{{cite journal |last1=Stuart |first1=Alexander M. |last2=Pame |first2=Anny Ruth P. |last3=Vithoonjit |first3=Duangporn |last4=Viriyangkura |first4=Ladda |last5=Pithuncharurnlap |first5=Julmanee |last6=Meesang |first6=Nisa |last7=Suksiri |first7=Prarthana |last8=Singleton |first8=Grant R. |last9=Lampayan | first9=Rubenito M. |year=2018 |title=The application of best management practices increases the profitability and sustainability of rice farming in the central plains of Thailand |url=https://www.researchgate.net/publication/314091782 |journal=Field Crops Research |volume=220 |pages=78–87 |doi=10.1016/j.fcr.2017.02.005 |access-date=12 September 2021 }}</ref> |
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Many farmers in tropical areas, however, struggle to retain organic matter and clay in the soils they work. In recent years, for example, productivity has declined and soil erosion has increased in the low-clay soils of northern Thailand, following the abandonment of [[shifting cultivation]] for a more permanent land use.<ref>{{cite journal |last1=Turkelboom |first1=Francis |last2=Poesen |first2=Jean |last3=Ohler |first3=Ilse |last4=Van Keer |first4=Koen |last5=Ongprasert |first5=Somchai |last6=Vlassak |first6=Karel |year=1997 |title=Assessment of tillage erosion rates on steep slopes in northern Thailand |url=https://www.academia.edu/17993140 |journal=Catena |volume=29 |issue=1 |pages=29–44 |doi=10.1016/S0341-8162(96)00063-X |access-date=12 September 2021 }}</ref> Farmers initially responded by adding organic matter and clay from [[Mound-building termites|termite mound]] material, but this was [[Sustainability|unsustainable]] in the long-term because of rarefaction of termite mounds. Scientists experimented with adding [[bentonite]], one of the smectite family of clays, to the soil. In field trials, conducted by scientists from the [[International Water Management Institute]] in cooperation with [[Khon Kaen University]] and local farmers, this had the effect of helping retain water and nutrients. Supplementing the farmer's usual practice with a single application of 200 kg bentonite per [[Rai (unit)|rai]] (6.26 rai = 1 hectare) resulted in an average yield increase of 73%.<ref>{{cite journal |last1=Saleth |first1=Rathinasamy Maria |last2=Inocencio |first2=Arlene |last3=Noble |first3=Andrew |last4=Ruaysoongnern |first4=Sawaeng |year=2009 |title=Economic gains of improving soil fertility and water holding capacity with clay application: the impact of soil remediation research in Northeast Thailand |url=https://ageconsearch.umn.edu/record/53064/files/RR130.pdf |journal=Journal of Development Effectiveness |volume=1 |issue=3 |pages=336–352 |doi=10.1080/19439340903105022 |s2cid=18049595 |access-date=12 September 2021 }}</ref> Other studies showed that applying bentonite to degraded sandy soils reduced the risk of crop failure during drought years.<ref>{{cite journal |last1=Semalulu |first1=Onesmus |last2=Magunda |first2=Matthias |last3=Mubiru |first3=Drake N. |year=2015 |title=Amelioration of sandy soils in drought stricken areas through use of Ca-bentonite |url=https://www.ajol.info/index.php/ujas/article/download/141752/131487 |journal=Uganda Journal of Agricultural Sciences |volume=16 |issue=2 |pages=195–205 |doi=10.4314/ujas.v16i2.5 |access-date=12 September 2021|doi-access=free }}</ref> |
Many farmers in tropical areas, however, struggle to retain organic matter and clay in the soils they work. In recent years, for example, productivity has declined and soil erosion has increased in the low-clay soils of northern Thailand, following the abandonment of [[shifting cultivation]] for a more permanent land use.<ref>{{cite journal |last1=Turkelboom |first1=Francis |last2=Poesen |first2=Jean |last3=Ohler |first3=Ilse |last4=Van Keer |first4=Koen |last5=Ongprasert |first5=Somchai |last6=Vlassak |first6=Karel |year=1997 |title=Assessment of tillage erosion rates on steep slopes in northern Thailand |url=https://www.academia.edu/17993140 |journal=Catena |volume=29 |issue=1 |pages=29–44 |doi=10.1016/S0341-8162(96)00063-X |access-date=12 September 2021 }}</ref> Farmers initially responded by adding organic matter and clay from [[Mound-building termites|termite mound]] material, but this was [[Sustainability|unsustainable]] in the long-term because of rarefaction of termite mounds. Scientists experimented with adding [[bentonite]], one of the smectite family of clays, to the soil. In field trials, conducted by scientists from the [[International Water Management Institute]] in cooperation with [[Khon Kaen University]] and local farmers, this had the effect of helping retain water and nutrients. Supplementing the farmer's usual practice with a single application of 200 kg bentonite per [[Rai (unit)|rai]] (6.26 rai = 1 hectare) resulted in an average yield increase of 73%.<ref>{{cite journal |last1=Saleth |first1=Rathinasamy Maria |last2=Inocencio |first2=Arlene |last3=Noble |first3=Andrew |last4=Ruaysoongnern |first4=Sawaeng |year=2009 |title=Economic gains of improving soil fertility and water holding capacity with clay application: the impact of soil remediation research in Northeast Thailand |url=https://ageconsearch.umn.edu/record/53064/files/RR130.pdf |journal=Journal of Development Effectiveness |volume=1 |issue=3 |pages=336–352 |doi=10.1080/19439340903105022 |s2cid=18049595 |access-date=12 September 2021 }}</ref> Other studies showed that applying bentonite to degraded sandy soils reduced the risk of crop failure during drought years.<ref>{{cite journal |last1=Semalulu |first1=Onesmus |last2=Magunda |first2=Matthias |last3=Mubiru |first3=Drake N. |year=2015 |title=Amelioration of sandy soils in drought stricken areas through use of Ca-bentonite |url=https://www.ajol.info/index.php/ujas/article/download/141752/131487 |journal=Uganda Journal of Agricultural Sciences |volume=16 |issue=2 |pages=195–205 |doi=10.4314/ujas.v16i2.5 |access-date=12 September 2021|doi-access=free }}</ref> |
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{{Main|Soil fertility}} |
{{Main|Soil fertility}} |
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{{Overly detailed|section|details=details could be moved into main article|date=April 2021}} |
{{Overly detailed|section|details=details could be moved into main article|date=April 2021}} |
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The Greek historian [[Xenophon]] (450–355 [[Before the Common Era|BCE]]) is credited with being the first to expound upon the merits of green-manuring crops: |
The Greek historian [[Xenophon]] (450–355 [[Before the Common Era|BCE]]) is credited with being the first to expound upon the merits of green-manuring crops: 'But then whatever weeds are upon the ground, being turned into earth, enrich the soil as much as dung.'{{sfn|Donahue|Miller|Shickluna|1977|p=4}} |
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[[Columella]]'s ''Of husbandry'', circa 60 [[Common Era|CE]], advocated the use of lime and that [[clover]] and [[alfalfa]] ([[green manure]]) should be turned under,<ref>{{cite book |last=Columella |first=Lucius Junius Moderatus |year=1745 |title=Of husbandry, in twelve books, and his book concerning trees, with several illustrations from Pliny, Cato, Varro, Palladius, and other antient and modern authors, translated into English |publisher=[[Andrew Millar]] |location=London, United Kingdom |url=https://catalog.hathitrust.org/Record/005783003 |access-date=19 September 2021}}</ref> and was used by 15 generations (450 years) under the [[Roman Empire]] until its collapse.{{sfn|Donahue|Miller|Shickluna|1977|p=4}}{{sfn|Kellogg|1957|p=1}} From the [[fall of Rome]] to the [[French Revolution]], knowledge of soil and agriculture was passed on from parent to child and as a result, crop yields were low. During the European [[Middle Ages]], [[Ibn al-'Awwam|Yahya Ibn al-'Awwam]]'s handbook,<ref>{{cite book |language=fr |last=[[Ibn al-'Awwam]] |year=1864 |title=Le livre de l'agriculture, traduit de l'arabe par Jean Jacques Clément-Mullet |publisher=Librairie A. Franck |location=Paris, France |url=https://catalog.hathitrust.org/Record/009953450 |access-date=19 September 2021}}</ref> with its emphasis on irrigation, guided the people of North Africa, Spain and the [[Middle East]]; a translation of this work was finally carried to the southwest of the United States when under Spanish influence.<ref>{{cite book |last=Jelinek |first=Lawrence J. |year=1982 |title=Harvest empire: a history of California agriculture |publisher=Boyd and Fraser |location=San Francisco, California |isbn=978-0-87835-131-2}}</ref> [[Olivier de Serres]], considered |
[[Columella]]'s ''Of husbandry'', circa 60 [[Common Era|CE]], advocated the use of lime and that [[clover]] and [[alfalfa]] ([[green manure]]) should be turned under,<ref>{{cite book |last=Columella |first=Lucius Junius Moderatus |year=1745 |title=Of husbandry, in twelve books, and his book concerning trees, with several illustrations from Pliny, Cato, Varro, Palladius, and other antient and modern authors, translated into English |publisher=[[Andrew Millar]] |location=London, United Kingdom |url=https://catalog.hathitrust.org/Record/005783003 |access-date=19 September 2021}}</ref> and was used by 15 generations (450 years) under the [[Roman Empire]] until its collapse.{{sfn|Donahue|Miller|Shickluna|1977|p=4}}{{sfn|Kellogg|1957|p=1}} From the [[fall of Rome]] to the [[French Revolution]], knowledge of soil and agriculture was passed on from parent to child and as a result, crop yields were low. During the European [[Middle Ages]], [[Ibn al-'Awwam|Yahya Ibn al-'Awwam]]'s handbook,<ref>{{cite book |language=fr |last=[[Ibn al-'Awwam]] |year=1864 |title=Le livre de l'agriculture, traduit de l'arabe par Jean Jacques Clément-Mullet |publisher=Librairie A. Franck |location=Paris, France |url=https://catalog.hathitrust.org/Record/009953450 |access-date=19 September 2021}}</ref> with its emphasis on irrigation, guided the people of North Africa, Spain and the [[Middle East]]; a translation of this work was finally carried to the southwest of the United States when under Spanish influence.<ref>{{cite book |last=Jelinek |first=Lawrence J. |year=1982 |title=Harvest empire: a history of California agriculture |publisher=Boyd and Fraser |location=San Francisco, California |isbn=978-0-87835-131-2}}</ref> [[Olivier de Serres]], considered the father of French [[agronomy]], was the first to suggest the abandonment of [[fallowing]] and its replacement by hay [[meadows]] within [[crop rotation]]s. He also highlighted the importance of soil (the French [[terroir]]) in the management of vineyards. His famous book {{Lang|fr|Le Théâtre d'Agriculture et mesnage des champs}}<ref>{{cite book |language=fr |last=de Serres |first=Olivier |year=1600 |title=Le Théâtre d'Agriculture et mesnage des champs |publisher=Jamet Métayer |location=Paris, France |url=https://gallica.bnf.fr/ark:/12148/bpt6k738381/f1.image |access-date=19 September 2021 }}</ref> contributed to the rise of modern, [[sustainable agriculture]] and to the collapse of old [[agricultural practices]] such as [[soil amendment]] for crops by the lifting of [[forest litter]] and [[assarting]], which ruined the soils of western Europe during the Middle Ages and even later on according to regions.<ref>{{cite journal |last1=Virto |first1=Iñigo |last2=Imaz |first2=María José |last3=Fernández-Ugalde |first3=Oihane |last4=Gartzia-Bengoetxea |first4=Nahia |last5=Enrique |first5=Alberto |last6=Bescansa |first6=Paloma |journal=[[Sustainability (journal)|Sustainability]] |volume=7 |issue=1 |title=Soil degradation and soil quality in western Europe: current situation and future perspectives |year=2015 |pages=313–365 |doi=10.3390/su7010313 |doi-access=free }}</ref> |
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Experiments into what made plants grow first led to the idea that the ash left behind when plant matter was burned was the essential element but overlooked the role of nitrogen, which is not left on the ground after combustion, a belief which prevailed until the 19th century.<ref>{{cite journal |last1=Van der Ploeg |first1=Rienk R. |last2=Schweigert |first2=Peter |last3=Bachmann |first3=Joerg |journal=[[Scientific World Journal]] |volume=1 |issue=S2 |title=Use and misuse of nitrogen in agriculture: the German story |year=2001 |pages=737–744 |doi=10.1100/tsw.2001.263 |pmid=12805882 |pmc=6084271 |doi-access=free }}</ref> In about 1635, the Flemish chemist [[Jan Baptist van Helmont]] thought he had proved water to be the essential element from his famous five years' experiment with a willow tree grown with only the addition of rainwater. His conclusion came from the fact that the increase in the plant's weight had apparently been produced only by the addition of water, with no reduction in the soil's weight.<ref>{{cite web |url=https://www.bbc.co.uk/bitesize/clips/zpgb4wx |title=Van Helmont's experiments on plant growth |website=[[BBC World Service]] |access-date=19 September 2021 }}</ref><ref name="Brady"/>{{sfn|Kellogg|1957|p=3}} [[John Woodward (naturalist)|John Woodward]] ({{abbr|d.|died}} 1728) experimented with various types of water ranging from clean to muddy and found muddy water the best, and so he concluded that earthy matter was the essential element. Others concluded it was humus in the soil that passed some essence to the growing plant. Still others held that the vital growth principal was something passed from dead plants or animals to the new plants. At the start of the 18th century, [[Jethro Tull (agriculturist)|Jethro Tull]] demonstrated that it was beneficial to cultivate (stir) the soil, but his opinion that the stirring made the fine parts of soil available for plant absorption was erroneous.<ref name="Brady">{{cite book |last=Brady |first=Nyle C. |title=The nature and properties of soils |edition=9th |year=1984 |publisher=[[Collier Macmillan]] |location=New York, New York |isbn=978-0-02-313340-4 |url=https://archive.org/details/natureproperties00brad_0 |access-date=19 September 2021}}</ref>{{sfn|Kellogg|1957|p=2}} |
Experiments into what made plants grow first led to the idea that the ash left behind when plant matter was burned was the essential element but overlooked the role of nitrogen, which is not left on the ground after combustion, a belief which prevailed until the 19th century.<ref>{{cite journal |last1=Van der Ploeg |first1=Rienk R. |last2=Schweigert |first2=Peter |last3=Bachmann |first3=Joerg |journal=[[Scientific World Journal]] |volume=1 |issue=S2 |title=Use and misuse of nitrogen in agriculture: the German story |year=2001 |pages=737–744 |doi=10.1100/tsw.2001.263 |pmid=12805882 |pmc=6084271 |doi-access=free }}</ref> In about 1635, the Flemish chemist [[Jan Baptist van Helmont]] thought he had proved water to be the essential element from his famous five years' experiment with a willow tree grown with only the addition of rainwater. His conclusion came from the fact that the increase in the plant's weight had apparently been produced only by the addition of water, with no reduction in the soil's weight.<ref>{{cite web |url=https://www.bbc.co.uk/bitesize/clips/zpgb4wx |title=Van Helmont's experiments on plant growth |website=[[BBC World Service]] |access-date=19 September 2021 }}</ref><ref name="Brady"/>{{sfn|Kellogg|1957|p=3}} [[John Woodward (naturalist)|John Woodward]] ({{abbr|d.|died}} 1728) experimented with various types of water ranging from clean to muddy and found muddy water the best, and so he concluded that earthy matter was the essential element. Others concluded it was humus in the soil that passed some essence to the growing plant. Still others held that the vital growth principal was something passed from dead plants or animals to the new plants. At the start of the 18th century, [[Jethro Tull (agriculturist)|Jethro Tull]] demonstrated that it was beneficial to cultivate (stir) the soil, but his opinion that the stirring made the fine parts of soil available for plant absorption was erroneous.<ref name="Brady">{{cite book |last=Brady |first=Nyle C. |title=The nature and properties of soils |edition=9th |year=1984 |publisher=[[Collier Macmillan]] |location=New York, New York |isbn=978-0-02-313340-4 |url=https://archive.org/details/natureproperties00brad_0 |access-date=19 September 2021}}</ref>{{sfn|Kellogg|1957|p=2}} |
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As chemistry developed, it was applied to the investigation of soil fertility. The French chemist [[Antoine Lavoisier]] showed in about 1778 that plants and animals must [[Combustion|combust]] oxygen internally to live |
As chemistry developed, it was applied to the investigation of soil fertility. The French chemist [[Antoine Lavoisier]] showed in about 1778 that plants and animals must [[Combustion|combust]] oxygen internally to live. He was able to deduce that most of the {{convert|165|lb|adj=on}} weight of van Helmont's willow tree derived from air.<ref>{{cite journal |language=fr |last=de Lavoisier |first=Antoine-Laurent |journal=Mémoires de l'Académie Royale des Sciences |title=Mémoire sur la combustion en général |year=1777 |url=http://www.academie-sciences.fr/pdf/dossiers/Franklin/Franklin_pdf/Mem1777_p592.pdf |access-date=19 September 2021}}</ref> It was the French agriculturalist [[Jean-Baptiste Boussingault]] who by means of experimentation obtained evidence showing that the main sources of carbon, hydrogen and oxygen for plants were air and water, while nitrogen was taken from soil.<ref>{{cite book |language=fr |last=Boussingault |first=Jean-Baptiste |title=Agronomie, chimie agricole et physiologie, volumes 1–5 |year=1860–1874 |publisher=Mallet-Bachelier |location=Paris, France |url=https://archive.org/details/8TSUP364_1 |access-date=19 September 2021}}</ref> [[Justus von Liebig]] in his book ''Organic chemistry in its applications to agriculture and physiology'' (published 1840), asserted that the chemicals in plants must have come from the soil and air and that to maintain soil fertility, the used minerals must be replaced.<ref>{{cite book |last=von Liebig |first=Justus |title=Organic chemistry in its applications to agriculture and physiology |year=1840 |publisher=Taylor and Walton |location=London |url=https://archive.org/details/organicchemistry00liebrich |access-date=19 September 2021}}</ref> Liebig nevertheless believed the nitrogen was supplied from the air. The enrichment of soil with guano by the Incas was rediscovered in 1802, by [[Alexander von Humboldt]]. This led to its mining and that of Chilean nitrate and to its application to soil in the United States and Europe after 1840.<ref>{{cite journal |last=Way |first=J. Thomas |journal=Journal of the Royal Agricultural Society of England |title=On the composition and money value of the different varieties of guano |year=1849 |volume=10 |pages=196–230 |url=https://www.biodiversitylibrary.org/item/37078#page/220/mode/1up |access-date=19 September 2021}}</ref> |
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The work of Liebig was a revolution for agriculture, and so other investigators started experimentation based on it. In England [[John Bennet Lawes]] and [[Joseph Henry Gilbert]] worked in the [[Rothamsted Research|Rothamsted Experimental Station]], founded by the former, and {{Not a typo|(re)discovered}} that plants took nitrogen from the soil, and that salts needed to be in an available state to be absorbed by plants. Their investigations also produced the [[superphosphate]], consisting in the acid treatment of phosphate rock.{{sfn|Kellogg|1957|p=4}} This led to the invention and use of salts of potassium (K) and nitrogen (N) as fertilizers. Ammonia generated by the production of [[coke (fuel)|coke]] was recovered and used as fertiliser.<ref>{{cite web |last=Tandon |first=Hari L.S. |url=http://www.tandontech.net/fertilisers.html |title=A short history of fertilisers |website=Fertiliser Development and Consultation Organisation |access-date=17 December 2017 |archive-url=https://web.archive.org/web/20170123214241/http://www.tandontech.net/fertilisers.html |archive-date=23 January 2017 |url-status=dead }}</ref> Finally, the chemical basis of nutrients delivered to the soil in manure was understood and in the mid-19th century chemical fertilisers were applied. However, the dynamic interaction of soil and its life forms still |
The work of Liebig was a revolution for agriculture, and so other investigators started experimentation based on it. In England [[John Bennet Lawes]] and [[Joseph Henry Gilbert]] worked in the [[Rothamsted Research|Rothamsted Experimental Station]], founded by the former, and {{Not a typo|(re)discovered}} that plants took nitrogen from the soil, and that salts needed to be in an available state to be absorbed by plants. Their investigations also produced the [[superphosphate]], consisting in the acid treatment of phosphate rock.{{sfn|Kellogg|1957|p=4}} This led to the invention and use of salts of potassium (K) and nitrogen (N) as fertilizers. Ammonia generated by the production of [[coke (fuel)|coke]] was recovered and used as fertiliser.<ref>{{cite web |last=Tandon |first=Hari L.S. |url=http://www.tandontech.net/fertilisers.html |title=A short history of fertilisers |website=Fertiliser Development and Consultation Organisation |access-date=17 December 2017 |archive-url=https://web.archive.org/web/20170123214241/http://www.tandontech.net/fertilisers.html |archive-date=23 January 2017 |url-status=dead }}</ref> Finally, the chemical basis of nutrients delivered to the soil in manure was understood and in the mid-19th century chemical fertilisers were applied. However, the dynamic interaction of soil and its life forms was still not understood. |
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In 1856, J. Thomas Way discovered that ammonia contained in fertilisers was transformed into nitrates,<ref>{{cite journal |last=Way |first=J. Thomas |journal=Journal of the Royal Agricultural Society of England |title=On the power of soils to absorb manure |year=1852 |volume=13 |pages=123–143 |url=https://biodiversitylibrary.org/page/45583402 |access-date=19 September 2021 }}</ref> and twenty years later [[Robert Warington]] proved that this transformation was done by living organisms.<ref>{{cite book |last=Warington |first=Robert |title=Note on the appearance of nitrous acid during the evaporation of water: a report of experiments made in the Rothamsted laboratory |url=https://books.google.com/books?id=NlISAQAAMAAJ |year=1878 |publisher=[[Harrison and Sons]] |location=London, United Kingdom |access-date=19 September 2021 }}</ref> In 1890 [[Sergei Winogradsky]] announced he had found the bacteria responsible for this transformation.<ref>{{cite journal |language=fr |last=Winogradsky |first=Sergei |journal=[[Comptes Rendus de l'Académie des Sciences|Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences]] |title=Sur les organismes de la nitrification |year=1890 |volume=110 |issue=1 |pages=1013–1016 |url=https://gallica.bnf.fr/ark:/12148/bpt6k30663/f1087?lang=EN |access-date=19 September 2021}}</ref> |
In 1856, J. Thomas Way discovered that ammonia contained in fertilisers was transformed into nitrates,<ref>{{cite journal |last=Way |first=J. Thomas |journal=Journal of the Royal Agricultural Society of England |title=On the power of soils to absorb manure |year=1852 |volume=13 |pages=123–143 |url=https://biodiversitylibrary.org/page/45583402 |access-date=19 September 2021 }}</ref> and twenty years later [[Robert Warington]] proved that this transformation was done by living organisms.<ref>{{cite book |last=Warington |first=Robert |title=Note on the appearance of nitrous acid during the evaporation of water: a report of experiments made in the Rothamsted laboratory |url=https://books.google.com/books?id=NlISAQAAMAAJ |year=1878 |publisher=[[Harrison and Sons]] |location=London, United Kingdom |access-date=19 September 2021 }}</ref> In 1890 [[Sergei Winogradsky]] announced he had found the bacteria responsible for this transformation.<ref>{{cite journal |language=fr |last=Winogradsky |first=Sergei |journal=[[Comptes Rendus de l'Académie des Sciences|Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences]] |title=Sur les organismes de la nitrification |year=1890 |volume=110 |issue=1 |pages=1013–1016 |url=https://gallica.bnf.fr/ark:/12148/bpt6k30663/f1087?lang=EN |access-date=19 September 2021}}</ref> |
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The scientists who studied the soil in connection with agricultural practices had considered it mainly as a static substrate. However, soil is the result of evolution from more ancient geological materials, under the action of biotic and abiotic processes. After studies of the improvement of the soil commenced, other researchers began to study soil genesis and as a result also soil types and classifications. |
The scientists who studied the soil in connection with agricultural practices had considered it mainly as a static substrate. However, soil is the result of evolution from more ancient geological materials, under the action of biotic and abiotic processes. After studies of the improvement of the soil commenced, other researchers began to study soil genesis and as a result also soil types and classifications. |
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In 1860, in Mississippi, [[Eugene W. Hilgard]] (1833–1916) studied the relationship between rock material, climate, vegetation, and the type of soils that were developed. He realised that the soils were dynamic, and considered the classification of soil types.<ref>{{cite book |last=Hilgard |first=Eugene W. |title=Soils: their formation, properties, composition, and relations to climate and plant growth in the humid and arid regions |year=1907 |publisher=[[The Macmillan Company]] |location=London, United Kingdom |url=https://www.biodiversitylibrary.org/bibliography/24461 |access-date=19 September 2021}}</ref> Unfortunately his work was not continued. At about the same time, [[Friedrich Albert Fallou]] was describing soil profiles and relating soil characteristics to their formation as part of his professional work evaluating forest and farm land for the principality of [[Saxony]]. His 1857 book, {{Lang|de|Anfangsgründe der Bodenkunde}} (First principles of soil science) established modern soil science.<ref>{{cite book |language=de |last=Fallou |first=Friedrich Albert |title=Anfangsgründe der Bodenkunde |year= 1857 |publisher=G. Schönfeld's Buchhandlung |location= Dresden, Germany |url=http://digital.slub-dresden.de/fileadmin/data/321768043/321768043_tif/jpegs/321768043.pdf |access-date=15 December 2018 |archive-url=https://web.archive.org/web/20181215223343/http://digital.slub-dresden.de/fileadmin/data/321768043/321768043_tif/jpegs/321768043.pdf |archive-date=15 December 2018 |url-status=dead}}</ref> Contemporary with Fallou's work, and driven by the same need to accurately assess land for equitable taxation, Vasily Dokuchaev led a team of soil scientists in Russia who conducted an extensive survey of soils, observing that similar basic rocks, climate and vegetation types lead to similar soil layering and types, and established the concepts for soil classifications. Due to language barriers, the work of this team was not communicated to western Europe until 1914 through a publication in German by [[Konstantin Glinka]], a member of the Russian team.<ref>{{cite book |language=de |last=Glinka |first=Konstantin Dmitrievich |title=Die Typen der Bodenbildung: ihre Klassifikation und geographische Verbreitung |year=1914 |publisher=[[Borntraeger]] |location=Berlin, Germany }}</ref> |
In 1860, while in Mississippi, [[Eugene W. Hilgard]] (1833–1916) studied the relationship between rock material, climate, vegetation, and the type of soils that were developed. He realised that the soils were dynamic, and considered the classification of soil types.<ref>{{cite book |last=Hilgard |first=Eugene W. |title=Soils: their formation, properties, composition, and relations to climate and plant growth in the humid and arid regions |year=1907 |publisher=[[The Macmillan Company]] |location=London, United Kingdom |url=https://www.biodiversitylibrary.org/bibliography/24461 |access-date=19 September 2021}}</ref> Unfortunately, his work was not continued. At about the same time, [[Friedrich Albert Fallou]] was describing soil profiles and relating soil characteristics to their formation as part of his professional work evaluating forest and farm land for the principality of [[Saxony]]. His 1857 book, {{Lang|de|Anfangsgründe der Bodenkunde}} (First principles of soil science) established modern soil science.<ref>{{cite book |language=de |last=Fallou |first=Friedrich Albert |title=Anfangsgründe der Bodenkunde |year= 1857 |publisher=G. Schönfeld's Buchhandlung |location= Dresden, Germany |url=http://digital.slub-dresden.de/fileadmin/data/321768043/321768043_tif/jpegs/321768043.pdf |access-date=15 December 2018 |archive-url=https://web.archive.org/web/20181215223343/http://digital.slub-dresden.de/fileadmin/data/321768043/321768043_tif/jpegs/321768043.pdf |archive-date=15 December 2018 |url-status=dead}}</ref> Contemporary with Fallou's work, and driven by the same need to accurately assess land for equitable taxation, Vasily Dokuchaev led a team of soil scientists in Russia who conducted an extensive survey of soils, observing that similar basic rocks, climate and vegetation types lead to similar soil layering and types, and established the concepts for soil classifications. Due to language barriers, the work of this team was not communicated to western Europe until 1914 through a publication in German by [[Konstantin Glinka]], a member of the Russian team.<ref>{{cite book |language=de |last=Glinka |first=Konstantin Dmitrievich |title=Die Typen der Bodenbildung: ihre Klassifikation und geographische Verbreitung |year=1914 |publisher=[[Borntraeger]] |location=Berlin, Germany }}</ref> |
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[[Curtis F. Marbut]], influenced by the work of the Russian team, translated Glinka's publication into English,<ref>{{cite book |last=Glinka |first=Konstantin Dmitrievich |title=The great soil groups of the world and their development |url=http://reader.library.cornell.edu/docviewer/digital?id=chla3055800#mode/1up |year=1927 |publisher=Edwards Brothers |location=Ann Arbor, Michigan |access-date=19 September 2021}}</ref> and as he was placed in charge of the U.S. [[National Cooperative Soil Survey]], applied it to a national soil classification system.<ref name="Brady"/> |
[[Curtis F. Marbut]], influenced by the work of the Russian team, translated Glinka's publication into English,<ref>{{cite book |last=Glinka |first=Konstantin Dmitrievich |title=The great soil groups of the world and their development |url=http://reader.library.cornell.edu/docviewer/digital?id=chla3055800#mode/1up |year=1927 |publisher=Edwards Brothers |location=Ann Arbor, Michigan |access-date=19 September 2021}}</ref> and, as he was placed in charge of the U.S. [[National Cooperative Soil Survey]], applied it to a national soil classification system.<ref name="Brady"/> |
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==See also== |
==See also== |
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{{portal|Environment|Geology}} |
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{{Commons category|Soils}} |
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* [[Acid sulfate soil]] |
* [[Acid sulfate soil]] |
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* [[Red soil]] |
* [[Red soil]] |
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}} |
}} |
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{{clear}} |
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==References== |
==References== |
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==External links== |
==External links== |
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{{wikt|soil}} |
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{{wikiversity|Soil Formation}} |
{{wikiversity|Soil Formation}} |
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{{Wikibooks |Historical Geology|Soils and paleosols}} |
{{Wikibooks |Historical Geology|Soils and paleosols}} |
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{{Commonscat|Soils}} |
{{Commonscat|Soils}} |
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*[https://www.theguardian.com/environment/video/2019/jul/11/its-time-we-stopped-treating-soil-like-dirt-video Short video explaining soil basics] |
*[https://www.theguardian.com/environment/video/2019/jul/11/its-time-we-stopped-treating-soil-like-dirt-video Short video explaining soil basics] |