{{Short description|Ability of a soil to sustain agricultural plant growth}} [[File:Soil Horizons.svg|thumb|Soil scientists use the capital letters O, A, B, C, and E to identify the master horizons, and lowercase letters for distinctions of these horizons. Most soils have three major horizons—the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but this horizon can also be buried. The master horizon, E, is used for subsurface horizons that have a significant loss of minerals (eluviation). Hard bedrock, which is not soil, uses the letter R.]] [[File:Desert East of Birdsville - panoramio (3).jpg|thumb|Desert east of [[Birdsville]], [[Australia]]. Much of Australia is [[population density|sparsely populated]] as its desert soils are mostly infertile; thus unable to support larger scale human habitation.<ref>{{cite web |url=http://www.abc.net.au/quantum/info/q95-19-5.htm |title=A chat with Tim Flannery on population control |last=Kelly |first=Karina |publisher=[[Australian Broadcasting Corporation]] |date=13 September 1995 |access-date=23 April 2010 |archive-url=https://web.archive.org/web/20100113095438/http://www.abc.net.au/quantum/info/q95-19-5.htm |archive-date=13 January 2010 |url-status=dead |quote=Well, Australia has by far the world's least fertile soils.}}</ref><ref>{{cite web |title=Damaged dirt |work=[[The Advertiser (Adelaide)|The Advertiser]] |last=Grant |first=Cameron |url=http://www.1degree.com.au/files/AdvertiserPartworks_Part3_Page8.pdf?download=1&filename=AdvertiserPartworks_Part3_Page8.pdf |archive-url=https://web.archive.org/web/20110706100423/http://www.1degree.com.au/files/AdvertiserPartworks_Part3_Page8.pdf?download=1&filename=AdvertiserPartworks_Part3_Page8.pdf |archive-date=6 July 2011 |date=August 2007 |access-date=23 April 2010 |url-status=dead |quote=Australia has the oldest, most highly weathered soils on the planet.}}</ref>]] '''Soil fertility''' refers to the ability of [[soil]] to sustain agricultural [[plant growth]], i.e. to provide plant [[habitat]] and result in sustained and consistent [[Crop yield|yields]] of high quality (see also [[soil health]]).<ref>{{cite journal |last1=Xing |first1=Yingying |last2=Wang |first2=Xiukang |last3=Mustafa |first3=Adnan |journal=[[Ecotoxicology and Environmental Safety]] |volume=289 |article-number=117703 |title=Exploring the link between soil health and crop productivity |date=1 January 2025 |doi=10.1016/j.ecoenv.2025.117703 |doi-access=free |pmid=39808880 |bibcode=2025EcoES.28917703X }}</ref> A fertile soil has the following properties:<ref>{{cite web |title=Soil fertility |url=http://www.fao.org/ag/agp/agpc/doc/publicat/FAOBUL4/FAOBUL4/B401.htm |website=www.fao.org |access-date=18 June 2016 |archive-date=24 November 2017 |archive-url=https://web.archive.org/web/20171124155743/http://www.fao.org/ag/agp/agpc/doc/publicat/faobul4/faobul4/b401.htm |url-status=dead }}</ref> * The ability to supply [[Plant nutrition|essential plant nutrients]] and water in adequate amounts and proportions for plant growth and reproduction; and * The absence of [[Phytotoxicity|toxic substances]] which may inhibit plant growth e.g. Fe<sup>2+</sup> which leads to nutrient [[toxicity]].
The following properties contribute to soil fertility in most situations: * Sufficient soil depth for adequate root growth and [[Soil water (retention)|water retention]]; * Good internal [[drainage]], allowing sufficient [[soil aeration]] for optimal root growth (although some plants, such as [[rice]], tolerate [[Waterlogging (agriculture)|waterlogging]]); * Topsoil or [[Soil horizon|horizon O]] is with sufficient [[soil organic matter]] for healthy [[soil structure]] and [[soil moisture]] retention; * [[Soil pH]] in the range 5.5 to 7.0 (suitable for most plants but some prefer or tolerate more acid or alkaline conditions); * Adequate concentrations of [[Plant nutrition|essential plant nutrients]] in plant-available forms; * Presence of a range of [[soil life|microorganisms]] that support plant growth.
In lands used for [[agriculture]] and other human activities, maintenance of soil fertility typically requires the use of [[soil conservation]] practices. This is because [[soil erosion]] and other forms of [[soil degradation]] generally result in a decline in [[soil quality]] with respect to one or more of the aspects indicated above.
Soil fertility and quality of land have been impacted by the effects of [[colonialism]] and [[slavery]] both in the U.S. and globally.<ref name="Blakie1987">{{cite book |last1=Blaikie |first1=Piers |last2=Brookfield |first2=Harold |chapter=Colonialism, development and degradation |chapter-url=https://www.libs.uga.edu/reserves/docs/scans/land%20degradation%20and%20society%20chapter%206.pdf |pages=100–21 |title=Land degradation and society |editor-last1=Blaikie |editor-first1=Piers |editor-last2=Brookfield |editor-first2=Harold |year=1987 |doi=10.4324/9781315685366 |isbn=9781315685366 |publisher=[[Routledge]] |location=Abingdon-on-Thames, United Kingdom |access-date=16 January 2026 }}</ref> The introduction of harmful land practices such as intensive and non-prescribed burnings and [[deforestation]] by [[colonist]]s created long-lasting negative results to the environment.<ref>{{cite web |url=https://vc.bridgew.edu/cgi/viewcontent.cgi?params=/context/honors_proj/article/1131/&path_info=Wood.pdf |title=The environmental impacts of colonialism |last=Wood |first=Lawrence |website=[[Bridgewater State University]] |date=17 December 2015 |access-date=16 January 2026 }}</ref> Also, the rise of [[intensive farming]] and intensive [[sylviculture]] contributed to the collapse of [[soil quality]] in [[Developed country|developed countries]].<ref>{{cite journal |last1=Virto |first1=Iñigo |last2=Imaz |first2=Maria José |last3=Fernández-Ugalde |first3=Oihane |last4=Gartzia-Bengoetxea |first4=Nahia |last5=Enrique |first5=Alberto |last6=Bescansa |first6=Paloma |journal=Sustainability |volume=7 |issue=1 |pages=313–65 |title=Soil degradation and soil quality in western Europe: current situation and future perspectives |date=31 December 2014 |doi=10.3390/su7010313 |doi-access=free |bibcode=2014Sust....7..313V |hdl=2454/26163 |hdl-access=free }}</ref>
Soil fertility and depletion have different origins and consequences in various parts of the world. The intentional creation of [[Terra preta|dark earth]] in the [[Amazon rainforest|Amazon]] promoted the tight relationship between [[Indigenous peoples of the Americas|indigenous]] communities and their land during [[Pre-Columbian era|Pre-Columbian]] times and are still searched as areas of high fertility.<ref>{{cite journal |last1=Lima |first1=Hedinaldo N. |last2=Schaefer |first2=Carlos E. R. |last3=Mello |first3=Jaime W. V. |last4=Gilkes |first4=Robert J. |last5=Ker |first5=João C. |journal=Geoderma |volume=110 |issue=1–2 |pages=1–17 |title=Pedogenesis and pre-Colombian land use of "Terra Preta Anthrosols" ("Indian black earth") of Western Amazonia |date=November 2002 |doi=10.1016/S0016-7061(02)00141-6 |bibcode=2002Geode.110....1L |url=https://www.researchgate.net/publication/200736466 |access-date=16 January 2026 }}</ref> In [[Africa]]n and [[Middle East]]ern regions, humans and the environment are also altered due to [[Soil Depletion|soil depletion]].<ref>{{cite journal |last1=Pourreza |first1=Aboulghasem |last2=Sadeghi |first2=Ahmad |last3=Amini-Rarani |first3=Mostafa |last4=Khodayari-Zarnaq |first4=Rahim |last5=Jafari |first5=Hasan |journal=Journal of Health, Population and Nutrition |volume=40 |article-number=11 |title=Contributing factors to the total fertility rate declining trend in the Middle East and North Africa: a systemic review |date=25 March 2021 |issue=1 |doi=10.1186/s41043-021-00239-w |doi-access=free |pmid=33766144 |pmc=7992960 |bibcode=2021JHPN...40...11P }}</ref>
== Soil fertilization == {{Main|Fertilizer}} [[Bioavailability|Bioavailable]] [[phosphorus]] (available to soil life) is the element in soil that is most often lacking, in particular in humid tropical soils.<ref>{{cite journal |last1=Lie |first1=Zhiyang |last2=Zhou |first2=Guoyi |last3=Huang |first3=Wenjuan |last4=Kadowaki |first4=Kohmei |last5=Tissue |first5=David T. |last6=Yan |first6=Junhua |last7=Peñuelas |first7=Josep |last8=Sardans |first8=Jordi |last9=Li |first9=Yuelin |last10=Liu |first10=Shizhong |last11=Chu |first11=Guowei |last12=Meng |first12=Ze |last13=He |first13=Xinhua |last14=Liu |first14=Juxiu |journal=[[Global Change Biology]] |volume=28 |issue=13 |pages=4085–93 |title=Warming drives sustained plant phosphorus demand in a humid tropical forest |date=12 April 2022 |doi=10.1111/gcb.16194 |pmid=35412664 |bibcode=2022GCBio..28.4085L |url=https://www.researchgate.net/publication/359910133 |access-date=16 January 2026 }}</ref> [[Nitrogen]] and [[potassium]] are also needed in substantial amounts.<ref>{{cite web |url=http://www2.mans.edu.eg/projects/heepf/ilppp/cources/12/pdf%20course/38/Nutrient%20Management%20for%20CCA.pdf |title=Soil fertility basics: NC Certified Crop Advisor Training |last=Hodges |first=Steven C. |website=[[North Carolina State University]], Soil Science Extension |year=2010 |access-date=16 January 2026 }}</ref> For this reason these three elements are always identified on a commercial fertilizer analysis. For example, a 10-10-15 fertilizer has 10 percent nitrogen, 10 percent available phosphorus (P<sub>2</sub>O<sub>5</sub>) and 15 percent water-soluble potassium (K<sub>2</sub>O). [[Sulfur]] is the fourth element that may be identified in a commercial analysis—e.g. 21-0-0-24 which would contain 21% nitrogen and 24% sulfate.
Inorganic fertilizers are generally less labour intensive and have higher concentrations of nutrients than organic fertilizers.<ref>{{cite journal |last1=Gupta |first1=Arti |last2=Hussain |first2=Nisreen |journal=[[Journal of Industrial Pollution Control]] |volume=30 |issue=2 |pages=191–3 |title=A critical study on the use, application and effectiveness of organic and inorganic fertilizers |date=January 2014 |url=https://www.icontrolpollution.com/articles/a-critical-study-on-the-use-application-and-effectiveness-191-194.pdf |access-date=16 January 2026 }}</ref> Also, since nitrogen, phosphorus and potassium generally must be in the inorganic forms to be taken up by plants, inorganic fertilizers are generally immediately bioavailable to plants without modification.<ref>{{cite book |last1=Weil |first1=Ray R. |last2=Brady |first2=Nyle C. |chapter=Nitrogen and sulfur economy of soils |pages=583–642 |chapter-url=https://www.researchgate.net/publication/299156145 |title=The nature and properties of soils |edition=15th |editor-last1=Weil |editor-first1=Ray R. |editor-last2=Brady |editor-first2=Nyle C. |year=2017 |isbn=978-0-13-325448-8 |publisher=[[Pearson Education|Pearson Educatio]]n |location=London, United Kingdom |access-date=16 January 2026 }}</ref> However, studies suggest that chemical fertilizers have adverse health impacts on humans including the development of [[chronic disease]] from the [[toxin]]s.<ref>{{cite web |last=Khiatah |first=Bashar |title=The health impacts of chemical fertilizers |url=https://amosinstitute.com/blog/the-health-impacts-of-chemical-fertilizers/ |access-date=16 January 2026 |website=amosinstitute.com |language=en }}</ref> As for the environment, over-reliance on inorganic fertilizers disrupts the natural nutrient balance in the soil, resulting in lower [[soil quality]], loss of [[organic matter]], and higher chances for [[erosion]] in the soil.<ref>{{cite web |title=The impact of fertilizers on the environment: inorganic vs. organic |url=https://farmerline.co/the-impact-of-fertilizers-on-the-environment-inorganic-vs-organic/ |date=23 June 2023 |website=farmerline.co |access-date=16 January 2026 |language=en-US }}</ref>
Additionally, the water-soluble [[nitrate]] nitrogen in inorganic fertilizers does not provide for the long-term needs of the plant and creates [[water pollution]].<ref>{{cite journal |last1=Bijay-Singh |last2=Craswell |first2=Eric |journal=[[SN Applied Sciences]] |volume=3 |article-number=518 |title=Fertilizers and nitrate pollution of surface and ground water: an increasingly pervasive global problem |date=31 March 2021 |issue=4 |doi=10.1007/s42452-021-04521-8 |url=https://www.researchgate.net/publication/350524887 |access-date=16 January 2026 |hdl=1885/267455 |hdl-access=free }}</ref> [[Slow-release fertilizer]]s may reduce [[Leaching (agriculture)|leaching]] loss of nutrients and may make the nutrients that they provide available over a longer period of time.<ref>{{cite journal |last=Guertal |first=Elizabeth A. |journal=HortTechnology |volume=19 |issue=1 |pages=16–19 |title=Slow-release nitrogen fertilizers in vegetable production: a review |date=1 January 2009 |doi=10.21273/HORTTECH.19.1.16 |doi-access=free }}</ref>
Soil fertility is a complex process that involves the constant [[Nutrient cycle|cycling of nutrients]] between organic and inorganic forms. As plant material and animal wastes are decomposed by micro-organisms, they release inorganic nutrients to the soil solution, a process referred to as [[mineralization (soil science)|mineralization]]. Those nutrients may then undergo further transformations which may be aided or enabled by soil [[Microorganism|micro-organisms]]. Like plants, many micro-organisms require or preferentially use inorganic forms of nitrogen, phosphorus or potassium and will compete with plants for these nutrients,<ref>{{cite journal |last1=Zhu |first1=Qing |last2=Riley |first2=William J. |last3=Tanj |first3=Jinyun |journal=[[Ecological Applications]] |volume=27 |issue=3 |pages=875–86 |title=A new theory of plant-microbe nutrient competition resolves inconsistencies between observations and model predictions |date=23 December 2016 |doi=10.1002/eap.1490 |pmid=28008686 |url=https://www.researchgate.net/publication/311860633 |access-date=16 January 2026 }}</ref> tying up the nutrients in microbial [[biomass]], a process often called [[Immobilization (soil science)|immobilization]]. The balance between immobilization and mineralization processes depends on the balance and availability of major nutrients and organic carbon to soil microorganisms.<ref>{{cite journal |last1=Sims |first1=Gerald K. |last2=Wander |first2=Michelle M. |journal=Applied Soil Ecology |volume=19 |issue=3 |pages=217–21 |title=Proteolytic activity under nitrogen or sulfur limitation |date=March 2002 |doi=10.1016/S0929-1393(01)00192-5 |bibcode=2002AppSE..19..217S |url=https://www.academia.edu/20293145 |access-date=16 January 2026 }}</ref><ref>{{cite journal |last=Sims |first=Gerald K. |journal=[[Soil Biology and Biochemistry]] |volume=38 |issue=8 |pages=2478–80 |title=Nitrogen starvation promotes biodegradation of N-heterocyclic compounds in soil |date=August 2006 |doi=10.1016/j.soilbio.2006.01.006 |bibcode=2006SBiBi..38.2478S |url=https://www.academia.edu/53004649 |access-date=16 January 2026 }}</ref> Natural processes such as [[lightning strike]]s may fix atmospheric nitrogen by converting it to [[nitric oxide]] (NO) and [[nitrogen dioxide]] (NO<sub>2</sub>).<ref>{{cite journal |last1=Drapcho |first1=David L. |last2=Sisterson |first2=Douglas |last3=Kumar |first3=Romesh |journal=[[Atmospheric Environment]] |volume=17 |issue=4 |pages=729–34 |title=Nitrogen fixation by lightning activity in a thunderstorm |year=1983 |doi=10.1016/0004-6981(83)90420-1 |bibcode=1983AtmEn..17..729D |url=https://www.academia.edu/27768416 |access-date=19 January 2026 }}</ref> In soil, nitrogen fixation is performed by free-living and symbiotic bacteria.<ref>{{cite journal |last=Stewart |first=William Duncan Paterson |journal=[[Proceedings: Biological Sciences|Proceedings B]] |volume=172 |issue=1029 |pages=367–88 |title=Biological and ecological aspects of nitrogen fixation by free-living micro-organisms |date=April 1969 |doi=10.1098/rspb.1969.0027 |pmid=4389402 |bibcode=1969RSPSB.172..367S |url=https://z-library.sk/book/53377014/29de44 |access-date=19 January 2026 }}</ref><ref>{{cite journal |last1=Mylona |first1=Panagiota |last2=Pawlowski |first2=Katharina |last3=Bisseling |first3=Ton |journal=[[The Plant Cell]] |volume=7 |issue=7 |pages=869–85 |title=Symbiotic nitrogen fixation |date=July 1995 |doi=10.1105/tpc.7.7.869 |pmid=12242391 |pmc=160880 |url=https://www.academia.edu/11654548 |access-date=21 January 2026 }}</ref> [[Denitrification]] occurs generally under [[Hypoxia (environmental)|anaerobic]] conditions (e.g. [[flooding]], [[Waterlogging (agriculture)|waterlogging]], [[particulate organic matter]], [[soil aggregate]]s) in the presence of [[denitrifying bacteria]],<ref>{{cite journal |last1=Wang |first1=Yong |last2=Uchida |first2=Yoshitaka |last3=Shimomura |first3=Yumi |last4=Akiyama |first4=Hiroko |last5=Hayatsu |first5=Masahito |journal=[[Scientific Reports]] |volume=7 |article-number=803 |title=Responses of denitrifying bacterial communities to short-term waterlogging of soils |date=11 April 2017 |issue=1 |doi=10.1038/s41598-017-00953-8 |doi-access=free |pmid=28400580 |pmc=5429771 |bibcode=2017NatSR...7..803W }}</ref><ref>{{cite journal |last1=Schlüter |first1=Stephen |last2=Lucas |first2=Maik |last3=Grosz |first3=Balazs |last4=Ippisch |first4=Olaf |last5=Zawallich |first5=Jan |last6=He |first6=Hongxing |last7=Dechow |first7=Rene |last8=Kraus |first8=David |last9=Blagodatsky |first9=Sergey |last10=Senbaryam |first10=Mehmet |last11=Kravchenko |first11=Alexandra |last12=Vogel |first12=Hans-Jörg |last13=Well |first13=Reinhard |journal=Biology and Fertility of Soils |volume=61 |issue=3 |pages=343–65 |title=The anaerobic soil volume as a controlling factor of denitrification: a review |date=16 April 2024 |doi=10.1007/s00374-024-01819-8 |doi-access=free }}</ref> but it may also occur in aerobic environments where [[oxygen]] concentration is fluctuating and reduced carbon is available.<ref>{{cite journal |last1=Ji |first1=Bin |last2=Yang |first2=Kai |last3=Zhu |first3=Lei |last4=Jiang |first4=Yu |last5=Wang |first5=Hongyu |last6=Zhou |first6=Jun |last7=Zhang |first7=Huining |journal=[[Biotechnology and Bioprocess Engineering]] |volume=20 |issue=4 |pages=643–51 |title=Aerobic denitrification: a review of important advances of the last 30 years |date=25 September 2015 |doi=10.1007/s12257-015-0009-0 |url=https://www.researchgate.net/publication/283101751 |access-date=19 January 2026 }}</ref> Nutrient [[cation]]s, including [[potassium]] and many [[micronutrient]]s, are held in relatively strong [[Electrostatics|electrostatic]] interaction bonds with the negatively charged portions of the soil ([[Clay mineral|clay]], [[humus]]) in a process known as [[cation-exchange capacity|cation exchange]] which has a prominent influence on soil fertility.<ref>{{cite journal |last1=Moral |first1=Francisco J. |last2=Rebollo |first2=Francisco J. |journal=Journal of Soil Science and Plant Nutrition |volume=17 |issue=2 |pages=486–98 |title=Characterization of soil fertility using the Rasch model |date=June 2017 |doi=10.4067/S0718-95162017005000035 |doi-access=free }}</ref>
[[Phosphorus]] is a primary factor of soil fertility as it is essential for [[cell division]] and [[plant development]], especially in [[seedling]]s and young plants.<ref>{{cite web |date=2021 |title=Why phosphorus is important |url=https://www.dpi.nsw.gov.au/agriculture/soils/more-information/improvement/phosphorous |access-date=19 January 2026 |website=www.dpi.nsw.gov.au |language=en }}</ref><ref>{{cite journal |last1=Kavanová |first1=Monika |last2=Lattanzi |first2=Fernando Alfredo |last3=Grimoldi |first3=Agustín Alberto |last4=Schnyder |first4=Hans |journal=[[Plant Physiology (journal)|Plant Physiology]] |volume=141 |issue=2 |pages=766–75 |title=Phosphorus deficiency decreases cell division and elongation in grass leaves |date=June 2006 |doi=10.1104/pp.106.079699 |url=https://www.researchgate.net/publication/7133554 |access-date=19 January 2026 |pmc=1475472 }}</ref> However, phosphorus is becoming increasingly harder to find and its reserves are starting to be depleted due to its excessive use as a [[fertilizer]].<ref>{{cite journal |last1=Van Vuuren |first1=Detlef P. |last2=Bouwman |first2=Alexander F. |last3=Beusen |first3=Arthur H. W. |journal=[[Global Environmental Change]] |volume=20 |issue=3 |pages=428–39 |title=Phosphorus demand for the 1970–2100 period: a scenario analysis of resource depletion |date=August 2010 |doi=10.1016/j.gloenvcha.2010.04.004 |bibcode=2010GEC....20..428V |url=https://z-library.sk/book/49021222/34413d |access-date=20 January 2026 }}</ref> The widespread use of phosphorus in fertilizers has led to [[pollution]] and [[eutrophication]].<ref>{{cite web |last=Pearce |first=Fred |date=7 July 2011 |title=Phosphate: a critical resource misused and now running low |url=https://e360.yale.edu/features/phosphate_a_critical_resource_misused_and_now_running_out |access-date=20 January 2026 |website=[[Yale School of the Environment]] |language=en-US}}</ref><ref>{{cite journal |last1=Daniel |first1=T. C. |last2=Sharpley |first2=Andrew N. |last3=Lemunyon |first3=Jerry L. |journal=[[Journal of Environmental Quality]] |volume=27 |issue=2 |pages=251–7 |title=Agricultural phosphorus and eutrophication: a symposium overview |date=March–April 1998 |doi=10.2134/jeq1998.00472425002700020002x |bibcode=1998JEnvQ..27..251D |url=https://z-library.sk/book/103132424/8a0dfa |access-date=20 January 2026 }}</ref> The term [[peak phosphorus]] has been coined, due to the limited occurrence of [[rock phosphate]] in the world, estimating that U.S. peak phosphorus occurred in 1988 and for the world in 1989.<ref>{{cite journal |last1=Déry |first1=Patrick |last2=Anderson |first2=Bart |journal=[[Energy Bulletin]] |title=Peak phosphorus |date=13 August 2007 |url=https://www.academia.edu/1263781 |access-date=20 January 2026 }}</ref>
A wide variety of materials have been described as [[soil conditioner]]s due to their ability to improve [[soil quality]], including [[biochar]], offering multiple [[soil health]] benefits.<ref>{{cite journal |last1=Joseph |first1=Stephen |last2=Cowie |first2=Annette L. |last3=Van Zwieten |first3=Lukas |last4=Bolan |first4=Nanthi |last5=Budai |first5=Alice |last6=Buss |first6=Wolfram |last7=Cayuela |first7=Maria Luz |last8=Graber |first8=Ellen R. |last9=Ippolito |first9=James A. |last10=Kuzyakov |first10=Yakov |author-link10=Yakov Kuzyakov |last11=Luo |first11=Yu |last12=Ok |first12=Yong Sik |last13=Palansooriya |first13=Kumuduni N. |last14=Shepherd |first14=Jessica |last15=Stephens |first15=Scott |last16=Weng |first16=Zhee (Han) |last17=Lehmann |first17=Johannes |date=November 2021 |title=How biochar works, and when it doesn't: a review of mechanisms controlling soil and plant responses to biochar |journal=[[GCB Bioenergy]] |language=en |volume=13 |issue=11 |pages=1731–64 |doi=10.1111/gcbb.12885 |issn=1757-1707 |s2cid=237725246 |doi-access=free |bibcode=2021GCBBi..13.1731J |hdl=10072/407684 |hdl-access=free |author-link8=Ellen Graber}}</ref>
[[Food loss and waste|Food waste]] [[compost]] was found to have better [[soil improvement]] than [[manure]] based compost.<ref>{{cite journal |last1=Kelley |first1=Alicia J. |last2=Campbell |first2=David N. |last3=Wilkie |first3=Ann C. |last4=Maltais-Landry |first4=Gabriel |date=August 2022 |title=Compost composition and application rate have a greater impact on spinach yield and soil fertility benefits than feedstock origin |journal=[[Horticulturae]] |language=en |volume=8 |issue=8 |page=688 |doi=10.3390/horticulturae8080688 |doi-access=free |issn=2311-7524 }}</ref>
== Light and CO<sub>2</sub> limitations ==
[[Photosynthesis]] is the process whereby plants use [[light energy]] to drive [[chemical reaction]]s which convert CO<sub>2</sub> into [[sugar]]s. As such, all plants require access to both light and [[carbon dioxide]] to produce energy, grow and reproduce.
While typically limited by nitrogen, phosphorus and potassium, low levels of carbon dioxide can also act as a limiting factor on plant growth. Peer-reviewed and published scientific studies have shown that increasing CO<sub>2</sub> is highly effective at promoting plant growth up to levels over 300 ppm. Further increases in CO<sub>2</sub> can, to a very small degree, continue to increase net photosynthetic output.<ref>{{cite book |last1=Chapin |first1=F. Stuart III |last2= Matson |first2=Pamela A. |last3=Moon |first3=Harold A. |year=2011 |title=Principles of terrestrial ecosystem ecology |publisher=[[Springer Science+Business Media|Springer]] |edition=2nd |isbn=978-1-4419-9504-9 |url=https://www.academia.edu/92723477 |access-date=20 January 2026 }}</ref>
== Soil depletion ==
[[Soil Depletion|Soil depletion]] occurs when the components which contribute to fertility are removed and not replaced, and the conditions which support soil's fertility are not maintained. This leads to poor crop yields, now becoming a global problem.<ref name="Tan2007">{{cite journal |last1=Tan |first1=Zhengxi |last2=Lal |first2=Rattan |last3=Wiebe |first3=Keith D. |journal= [[Journal of Sustainable Agriculture]] |volume=26 |issue=1 |pages=123–46 |title=Global soil nutrient depletion and yield reduction |year=2005 |doi=10.1300/J064v26n01_10 |bibcode=2005JSusA..26a.123T |url=https://www.researchgate.net/publication/48855698 |access-date=20 January 2026 }}</ref> In agriculture, soil depletion can be due to excessively [[intensive cultivation]] and inadequate [[soil management]].<ref>{{cite journal |last1=Das |first1=Debarup |last2=Sahoo |first2=Jyotirmaya |last3=Rasa |first3=Md Basit |last4=Barman |first4=Mandira |last5=Das |first5=Ruma |date=13 January 2022 |title=Ongoing soil potassium depletion under intensive cropping in India and probable mitigation strategies: a review |journal=[[Agronomy for Sustainable Development]] |language=en |volume=42 |issue=1 |article-number=4 |doi=10.1007/s13593-021-00728-6 |bibcode=2022AgSD...42....4D |issn=1773-0155 |url=https://hal.science/hal-03940205/document |access-date=20 January 2026 }}</ref> Depletion may occur through a variety of other effects, including over-[[tillage]] (which damages [[soil structure]]),<ref>{{cite book |last1=Kay |first1=Bev D. |last2=Munkholm |first2=Lars Juhl |chapter=Management-induced soil structure degradation: organic matter depletion and tillage |pages=185–97 |chapter-url=https://www.researchgate.net/publication/276886797 |title=Managing soil quality: challenges in modern agriculture |editor-last1=Schjønning |editor-first1=Per |editor-last2=Elmholt |editor-first2=Susanne |editor-last3=Christensen |editor-first3=Bent T. |year=2004 |isbn=978-0-85199-671-4 |publisher=[[CABI Publishing]] |access-date=24 February 2026 }}</ref> overuse of nutrient inputs which leads to mining of the [[nutrient management|soil nutrient bank]],<ref name="Dallal1997">{{cite book |last1=Dallal |first1=Rattan C. |last2=Probert |first2=Merv E. |chapter=Soil nutrient depletion |pages=42–63 |chapter-url=https://www.researchgate.net/publication/291868075 |title=Sustainable crop production in the sub-tropics: an Australian perspective |editor-last1=Clarke |editor-first1=A. L. |editor-last2=Wylie |editor-first2=P. B. |year=1997 |isbn=978-0-7242-5985-4 |publisher=[[Queensland Department of Primary Industries]], Information Centre |location=Brisbane, Australia |access-date=20 January 2026 }}</ref> and [[Soil salinity|salinization]] of soil.<ref>{{cite journal |last1=Zhang |first1=Wen-wen |last2=Wang |first2=Chong |last3=Xue |first3=Rui |last4=Wang |first4=Li-jie |date=June 2019 |title=Effects of salinity on the soil microbial community and soil fertility |journal=Journal of Integrative Agriculture |language=en |volume=18 |issue=6 |pages=1360–8 |doi=10.1016/S2095-3119(18)62077-5 |bibcode=2019JIAgr..18.1360Z |issn=2352-3425 |doi-access=free }}</ref>
=== Colonial impacts on soil depletion ===
Soil fertility can be severely challenged when [[land-use change]]s rapidly. For example, in [[Colonial New England]], [[colonist]]s made a number of decisions that depleted the soils, including: allowing herd animals to wander freely, not replenishing soils with manure, and a sequence of events that led to erosion.<ref name="Cronon1983">{{cite book |last=Cronon |first=William |year=1983 |title=Changes in the land: Indians, colonists, and the ecology of New England |publisher=[[Hill & Wang]] |location=New York, New York |isbn=978-0809016341 |url=https://z-library.sk/book/120322124/1255ea |access-date=20 January 2026 }}</ref> [[William Cronon]] wrote that "...the long-term effect was to put those soils in jeopardy. The removal of the forest, the increase in destructive floods, the soil compaction and close-cropping wrought by grazing animals, ploughing—all served to increase erosion." Cronon continues, explaining, "Where mowing was unnecessary and grazing among living trees was possible, settlers saved labor by simply burning the forest undergrowth...and turning loose their cattle...In at least one ill-favored area, the inhabitants of neighboring towns burned so frequently and graze so intensively that...the timber was greatly injured, and the land became hard to subdue...In the long run, cattle tended to encourage the growth of woody, thorn-bearing plants which they could not eat and which, once established, were very difficult to remove". These practices were methods of simplifying labor for colonial settlers in new lands when they were not familiar with traditional [[Indigenous peoples of the Americas|Indigenous]] agricultural methods. Those Indigenous communities were not consulted but rather forced out of their [[homeland]]s so European settlers could commodify their resources. The practice of intensive land burning and turning loose cattle ruined soil fertility and prohibited [[Sustainability|sustainable]] crop growth.<ref name="Cronon1983"/>
While colonists utilized fire to clear land, certain [[prescribed burning]] practices are common and valuable to increase [[biodiversity]] and in turn, benefit soil fertility.<ref>{{cite book |last=McKee |first=William H. Jr |year=1982 |title=Changes in soil fertility following prescribed burning on Coastal Plain pine sites |publisher=[[USDA Forest Service]], [[Southern Research Station]] |location=Asheville, North Carolina |doi=10.2737/SE-RP-234 |url=https://www.srs.fs.usda.gov/pubs/rp/rp_se234.pdf |access-date=20 January 2026 }}</ref> However, without consideration of the intensity, seasonality, and frequency of the burns, the conservation of biodiversity and the overall health of the soil can be negatively impacted by fire.<ref>{{cite journal |last1=Pastro |first1=Louise A. |last2=Dickman |first2=Christopher R. |last3=Letnic |first3=Mike |date=December 2011 |title=Burning for biodiversity or burning biodiversity? Prescribed burn vs. wildfire impacts on plants, lizards, and mammals |url=https://www.researchgate.net/publication/259497103 |journal=[[Ecological Applications]] |language=en |volume=21 |issue=8 |pages=3238–53 |doi=10.1890/10-2351.1 |bibcode=2011EcoAp..21.3238P |issn=1051-0761 |access-date=20 January 2026 }}</ref>
In addition to [[soil erosion]] through using too much fire,<ref>{{cite journal |last1=Tempany |first1=Harold A. |last2=Roddan |first2=G. M. |last3=Lord |first3=L. |date=December 1944 |title=Soil erosion and soil conservation in the colonial empire |url=https://www.vetiver.org/UK_Colonial%20overview.pdf |journal=Empire Forestry Journal |language=en |volume=23 |issue=2 |pages=142–59 |issn=2055-5237 |access-date=20 January 2026 }}</ref> colonial agriculture also resulted in [[topsoil depletion]].<ref name="Blakie1987"/> Topsoil depletion occurs when the nutrient-rich organic [[topsoil]], which takes hundreds to thousands of years to build up under natural conditions,<ref>{{cite journal |last1=Zou |first1=Ping |last2=Fu |first2=Jianrong |last3=Cao |first3=Zhihong |last4=Ye |first4=Jing |last5=Yu |first5=Qiaogang |date=23 November 2014 |title=Aggregate dynamics and associated soil organic matter in topsoils of two 2,000-year paddy soil chronosequences |url=https://z-library.sk/book/71068522/7a3b39 |journal=Journal of Soils and Sediments |language=en |volume=15 |issue=3 |pages=510–22 |doi=10.1007/s11368-014-0977-2 |issn=1614-7480 |access-date=20 January 2026 }}</ref> is eroded or depleted of its original organic material. The [[Dust Bowl]] in the [[Great Plains]] of North America is a great example of this with about one-half of the original topsoil of the Great Plains having disappeared since the beginning of agricultural production there in the 1880s.<ref>{{cite journal |last=Lockeretz |first=William |date=September–October 1978 |title=The lessons of the Dust Bowl |url=https://z-library.sk/book/93728444/18c122 |journal=[[American Scientist]] |language=en |volume=66 |issue=5 |pages=560–9 |bibcode=1978AmSci..66..560L |issn=0003-0996 |access-date=20 January 2026 }}</ref> Outside of the context of colonialism, many past civilizations' collapses can be attributed to topsoil depletion.<ref>{{cite book |last=Kötke |first=William H. |title=The final empire: the collapse of civilization and the seed of the future |publisher=Arrow Point Press |location=Portland, Oregon |year=1993 |isbn=978-1434331298 |url=https://z-library.sk/book/120678447/91505e |access-date=21 January 2026 }}</ref>
=== Soil depletion and enslavement ===
As historian [[David Silkenat]] explains, the goals of Southern plantation and [[Slavery|slave]] owners, instead of measuring [[productivity]] based on outputs per acre, were to maximize the amount of labor that could be extracted from the enslaved [[workforce]]. The landscape was seen as disposable, and the African slaves were seen as expendable. Once these Southern farmers forced slaves to engage in mass [[deforestation]], they would discard the land and move towards more fertile prospects. The forced slave practices created extensive destruction on the land. The environmental impact included draining [[swamp]]s, clearing forests for [[monocropping]] and fuel [[steamship]]s, and introducing [[invasive species]], all leading to fragile [[ecosystem]]s. In the aftermath, these ecosystems left hillsides eroded, rivers clogged with sterile soil, and extinction of native species. [[David Silkenat|Silkenat]] summarizes this phenomenon of the relationship between enslavement and soil, "Although typically treated separately, slavery and the environment naturally intersect in complex and powerful ways, leaving lasting effects from the period of emancipation through modern-day reckonings with racial justice…the land too fell victim to the slave owner's lash".<ref>{{cite book |last=Silkenat |first=David |title=Scars on the land: an environmental history of slavery in the American South |date=24 March 2022 |publisher=[[Oxford University Press]] |isbn=978-0-19-756422-6 |edition=1st |language=en |doi=10.1093/oso/9780197564226.001.0001 |url=https://z-library.sk/book/23177419/a7aeb9 |access-date=21 January 2026 }}</ref>
=== Global Soil Depletion ===
One of the most widespread occurrences of soil depletion {{as of|lc=y|2008}} is in tropical zones where [[nutrient]] content of soils is low.<ref name="Dallal1997"/> The depletion of soil has affected the state of plant life and crops in agriculture in many countries.<ref name="Tan2007"/> In the [[Middle East]] for example, many countries find it difficult to grow produce because of [[drought]],<ref>{{cite journal |last1=Kaniewski |first1=Daniel |last2=Van Campo |first2=Elise |last3=Weiss |first3=Harvey |date=21 February 2012 |title=Drought is a recurring challenge in the Middle East |url=https://www.researchgate.net/publication/221851932 |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=109 |issue=10 |pages=3862–7 |doi=10.1073/pnas.1116304109 |issn=1091-6490 |access-date=21 January 2026 }}</ref> lack of soil ([[soil erosion]]),<ref>{{cite book |last=Mashhadi |first=Ali |chapter=Soil erosion and dust storm in Iran and the Middle East region from the perspective of international law |pages=463–76 |chapter-url=https://www.researchgate.net/publication/398583017 |title=International yearbook of soil law and policy 2025 |editor-last1=Ginsky |editor-first1=Harald |editor-last2=Grinlinton |editor-first2=David |editor-last3=Heuser |editor-first3=Irene L. |editor-last4=Kameri-Mbote |editor-first4=Patricia |editor-last5=Khatibi |editor-first5=Atieh |editor-last6=Rodriguez-Eugenio |editor-first6=Natalia |editor-last7=Ruppel |editor-first7=Oliver C. |year=2026 |isbn=978-3-032-03251-5 |doi=10.1007/978-3-032-03251-5_19 |publisher=Springer Cham |location=Cham, Switzerland |access-date=22 January 2026 }}</ref> and lack of [[irrigation]].<ref>{{cite journal |last=Smith |first=Christopher G. |date=November 1970 |title=Water resources and irrigation development in the Middle East |url=https://z-library.sk/book/78839535/5f95fe |journal=Geography |language=en |volume=55 |issue=4 |pages=407–25 |issn=2043-6564 |access-date=22 January 2026 }}</ref> The [[Middle East]] has three countries that indicate a decline in crop production, the highest rates of productivity decline being found in hilly and dryland areas.<ref>{{cite book |last1=Scherr |first1=Sara J. |last2=Yadav |first2=Satya |date=May 1996 |title=Land degradation in the developing world: implications for food, agriculture, and the environment to 2020 |url=https://cgspace.cgiar.org/server/api/core/bitstreams/4b57dd0a-2884-4cce-abe1-27af2ffdda2c/content |archive-url=https://web.archive.org/web/20120904000800/http://pdf.usaid.gov/pdf_docs/PNABY622.pdf |archive-date=4 September 2012 |publisher=[[International Food Policy Research Institute]] |pages=7–8 |access-date=21 January 2026 |url-status=live }}</ref>
Many countries in Africa also undergo a depletion of fertile soil, in particular in [[sub-Saharan Africa]] ([[Sahel]]) under high [[population pressure]].<ref>{{cite journal |last1=Drechsel |first1=Pay |last2=Kunze |first2=Dagmar |last3=De Vries |first3=Fritz Penning |date=March 2001 |title=Soil nutrient depletion and population growth in Sub-Saharan Africa: a Malthusian nexus? |url=https://z-library.sk/book/43188640/978d10 |journal=[[Population and Environment]] |language=en |volume=22 |issue=4 |pages=411–23 |doi=10.1023/A:1006701806772 |issn=1573-7810 |access-date=22 January 2026 }}</ref> In regions of [[arid climate]] like [[Sudan]] and the countries that make up the [[Sahara Desert]], droughts and soil degradation are common, aggravataed by badly-adapted [[agricultural practice]]s.<ref>{{cite journal |last=Ayoub |first=Ali Taha |journal=[[Journal of Arid Environments]] |volume=38 |issue=3 |pages=397–409 |title=Extent, severity and causative factors of land degradation in the Sudan |date=March 1998 |doi=10.1006/jare.1997.0346 |url=https://www.academia.edu/2144666 |access-date=23 February 2026 }}</ref> Cash crops such as teas, maize, and beans require a high variety and quantity of nutrients in order to grow healthy and sustain population growth.<ref>{{cite journal |last1=Ten Berge |first1=Hein F. M. |last2=Hijbeek |first2=Renske |last3=Van Loon |first3=Marloes P. |last4=Rurinda |first4=Jairos |last5=Tesfaye |first5=Kindie |last6=Zingore |first6=Shamie |last7=Craufurd |first7=Peter |last8=Van Heerwaarden |first8=Joost |last9=Brentrup |first9=Frank |last10=Schröder |first10=Jaap J. |last11=Boogaard |first11=Hendrik L. |last12=De Groot |first12=Hugo L. E. |last13=Van Ittersum |first13=Martin K. |journal=Global Food Security |volume=23 |pages=9–21 |title=Maize crop nutrient input requirements for food security in sub-Saharan Africa |date=December 2019 |doi=10.1016/j.gfs.2019.02.001 |url=https://www.researchgate.net/publication/332187377 |access-date=22 January 2026 }}</ref> Soil fertility has declined in the farming regions of Africa and the use of artificial and natural [[fertilizer]]s has been used to regain the nutrients of ground soil.<ref>{{cite book |last1=Smaling |first1=Eric M. A. |last2=Nandwa |first2=Stephen M. |last3=Janssen |first3=Bert H. |chapter=Soil fertility in Africa is at stake |title=Replenishing soil fertility in Africa |year=1997 |editor-last1=Buresh |editor-first1=Roland J. |editor-last2=Sanchez |editor-first2=Pedro A. |editor-last3=Calhoun |editor-first3=Frank |publisher=[[Soil Science Society of America]] |location=Madison, Wisconsin |pages=47–61 |chapter-url=https://scispace.com/pdf/soil-fertility-in-africa-is-at-stake-egsvjrjpz1.pdf |access-date=22 January 2026 }}</ref>
== Dark Earths ==
=== South America ===
The details of Indigenous societies prior to European colonization in 1492 within the [[Amazon rainforest|Amazonia]]n regions of South America, particularly the size of the communities and the depth of interactions with the environment, are continually debated. Central to the debate is the influence of [[Terra preta|Dark Earth]]. Dark Earth is a type of soil found in the Amazon that has a darker color, higher organic carbon content, and higher fertility than soil in other regions of South America, which makes it highly coveted even today.<ref>{{cite journal |last1=Kawa |first1=Nicholas C. |last2=Oyuela-Caycedo |first2=Augusto |journal=International Journal of Environmental Cultural Economic and Social Sustainability |volume=4 |issue=3 |pages=9–16 |title=Amazonian Dark Earth |year=2008 |doi=10.18848/1832-2077/CGP/v04i03/54453 |url=https://www.researchgate.net/publication/307763141 |access-date=22 January 2026 }}</ref> Dark Earth deposits have been found, through [[Ethnography|ethnographic]] and [[archaeological]] studies, to have been created through ancient Indigenous practices by intentional soil management.<ref name="Schmidt2023">{{cite journal |last1=Schmidt |first1=Morgan J. |last2=Goldberg |first2=Samuel L. |last3=Heckenberger |first3=Michael |last4=Fausto |first4=Carlos |last5=Franchetto |first5=Bruna |last6=Watling |first6=Jennifer |last7=Lima |first7=Helena |last8=Moraes |first8=Bruno |last9=Dorshow |first9=Wetherbee B. |last10=Toney |first10=Joshua |last11=Kuikuro |first11=Yamalui |last12=Waura |first12=Kumessi |last13=Kuikuro |first13=Huke |last14=Kuikuro |first14=Taku Wate |last15=Kuikuro |first15=Takumã |date=22 September 2023 |title=Intentional creation of carbon-rich dark earth soils in the Amazon |journal=[[Science Advances]] |language=en |volume=9 |issue=38 |article-number=eadh8499 |bibcode=2023SciA....9H8499S |doi=10.1126/sciadv.adh8499 |issn=2375-2548 |pmc=11320335 |pmid=37729404 |doi-access=free }}</ref>
[[Ethnoarchaeology|Ethnoarchaeologist]] Morgan Schmidt outlines how this carbon-rich soil was intentionally created by communities in the Amazon. While Dark Earth, and other anthropic soils, can be found all throughout the world, Amazonian Dark Earth is particularly significant because "it contrasts too sharply with the especially poor fertility of typical highly weathered tropical upland soils in the Amazon". There is much evidence to suggest that the development of ancient agricultural societies in the Amazon was strongly influenced by the formation of Dark Earth. As a result, Amazonian societies benefitted from the dark earth in terms of agricultural success and enhanced food production. Soil analyses have been completed on the modern and ancient [[Kuikuro]] Indigenous Territory in the Upper [[Xingu River]] basin in southeastern Amazonia through archaeological and ethnographic research to determine the human relation to the soil. The "results demonstrate the intentional creation of dark earth, highlighting how Indigenous knowledge can provide strategies for sustainable rainforest management". Present-day addition of orgnic waste products ([[fish]] and [[manioc]] [[refuse]]s), [[ash]]es and [[charcoal]] as mounds up to ~50 to 60 cm above the original ground surface by Kuikuro [[Amerindians]] was hypothesized to be common practice in [[Pre-Columbian era|Pre-Columbian]] agriculture.<ref name="Schmidt2023"/> By transforming charcoal in [[black carbon]], a source of highly stable [[humus]],<ref>{{cite journal |last1=Brodowski |first1=Sonja |last2=Amelung |first2=Wulf |last3=Haumaier |first3=Ludwig |last4=Zech |first4=Wolfgang |date=15 April 2007 |title=Black carbon contribution to stable humus in German arable soils |journal=Geoderma |language=en |volume=139 |issue=1–2 |pages=220–8 |doi=10.1016/j.geoderma.2007.02.004 |issn=0016-7061 |url=https://www.academia.edu/66772690 |access-date=22 January 2026 }}</ref> the grinding and mixing activity of the peregrine [[pantropical]] [[earthworm]] ''[[Pontoscolex corethrurus]]'' adds a natural biological phenomenon to our knowledge of the formation of the fertile Amazonian Dark Earths.<ref>{{cite journal |last1=Ponge |first1=Jean-François |last2=Topoliantz |first2=Stéphanie |last3=Ballof |first3=Sylvain |last4=Rossi |first4=Jean-Pierre |last5=Lavelle |first5=Patrick |last6=Betsch |first6=Jean-Marie |last7=Gaucher |first7=Phiippe |date=July 2006 |title=Ingestion of charcoal by the Amazonian earthworm ''Pontoscolex corethrurus'': a potential for tropical soil fertility |journal=[[Soil Biology and Biochemistry]] |language=en |volume=38 |issue=7 |pages=2008–9 |doi=10.1016/j.soilbio.2005.12.024 |issn=1879-3428 |url=https://www.academia.edu/44852813 |access-date=22 January 2026 }}</ref>
=== Africa ===
In [[Egypt]], earthworms of the [[Nile River]] Valley contributed to the significant fertility of the soils.<ref>{{cite book |last=Yadav |first=Shweta |chapter=Contribution of earthworm to bioremediation as a living machine: bioremediation |doi=10.4018/978-1-5225-2325-3.ch014 |title=Handbook of research on inventive bioremediation techniques |year=2017 |editor-last=Bhakta |editor-first=Jatindra Nath |isbn=978-1522523253 |publisher=[[IGI Global]] |location=Palmdale, Pennsylvania |pages=324–40 |chapter-url=https://www.researchgate.net/publication/312967557 |access-date=22 January 2026 }}</ref> As a result, [[Cleopatra]] declared the earthworm a sacred animal to be revered and protected by all her subjects. Egyptians were not allowed to remove so much as a single worm from the land of Egypt, and even farmers were not allowed to touch an earthworm for fear of offending the god of fertility.<ref>{{cite book |last=Minnich |first=Jerry |chapter=The earthworm through history |title=The earthworm book: how to raise and use earthworms for your farm and garden |year=1977 |editor-last=Minnich |editor-first=Jerry |isbn=9780878571932 |publisher=[[Rodale Press]] |location=Emmaus, Pennsylvania |pages=57–83 |chapter-url=https://archive.org/details/earthwormbookhow0000minn/page/56/mode/2up |access-date=22 January 2026 }}</ref> In Ghana and Liberia, it is a long-standing practice to combine different types of waste to create fertile soil that is referred to as African Dark Earths. This soil contains high concentrations of calcium, phosphorus, and carbon.<ref>{{cite journal |last1=Solomon |first1=Dawit |last2=Lehmann |first2=Johannes |last3=Fraser |first3=James A |last4=Leach |first4=Melissa |last5=Amanor |first5=Kojo |last6=Frausin |first6=Victoria |last7=Kristiansen |first7=Søren M |last8=Millimouno |first8=Dominique |last9=Fairhead |first9=James |date=March 2016 |title=Indigenous African soil enrichment as a climate-smart sustainable agriculture alternative |url=https://www.researchgate.net/publication/296619044 |journal=[[Frontiers in Ecology and the Environment]] |language=en |volume=14 |issue=2 |pages=71–76 |doi=10.1002/fee.1226 |bibcode=2016FrEE...14...71S |issn=1540-9295 |access-date=22 January 2026 }}</ref>
=== North America and Eurasia ===
Also called [[Mollisol]]s, [[Chernozem]]s or [[Black Soil]]s, with a number of variants, Dark Earths are widespread in [[North America]] and in a [[mid-latitude]] stretch extending over a large part of Eurasia.<ref>{{cite journal |last1=Liu |first1=Xiaobing |last2=Burras |first2=Charles Lee |last3=Kravchenko |first3=Yuri S. |last4=Duran |first4=Artigas |last5=Huffman |first5=Ted |last6=Morras |first6=Hector |last7=Studdert |first7=Guillermo |last8=Zhang |first8=Xingyi |last9=Cruse |first9=Richard M. |last10=Yuan |first10=Xiaohui |date=1 January 2012 |title=Overview of Mollisols in the world: distribution, land use and management |journal=[[Canadian Journal of Soil Science]] |language=en |volume=92 |issue=3 |pages=383–402 |doi=10.4141/cjss2010-058 |issn=1918-1841 |doi-access=free }}</ref> The formation of these fertile carbon- and nutrient-rich [[zonal soil]]s was longtime attributed to dry [[continental climate]] conditions and [[steppe]] or [[prairie]] vegetation (according to [[biome]]s)<ref>{{cite journal |last1=Eckmeier |first1=Eileen |last2=Gerlach |first2=Renate |last3=Gehrt |first3=Ernst |last4=Schmidt |first4=Michael W. I. |date=15 May 2007 |title=Pedogenesis of Chernozems in Central Europe: a review |journal=Geoderma |language=en |volume=139 |issue=3–4 |pages=288–99 |doi=10.1016/j.geoderma.2007.01.009 |issn=0016-7061 |url=https://www.researchgate.net/publication/222673118 |access-date=23 January 2026 }}</ref> until it became admitted that past [[human activities]] (deposition of domestic and occupational [[waste]]s, [[charred]] residues, biomass [[ash]]es, [[burning]], [[Fertilizer|fertilisation]]) were a driving factor of Dark Earth formation, and that not only in the [[tropics]].<ref>{{cite journal |last=Asare |first=Michael Opare |date=September–October 2022 |title=Anthropogenic dark earth: evolution, distribution, physical, and chemical properties |url=https://www.researchgate.net/publication/363772131 |journal=European Journal of Soil Science |language=en |volume=73 |issue=5 |article-number=e13308 |doi=10.1111/ejss.13308 |issn=1365-2389 |access-date=23 January 2026 }}</ref> The presence in the A horizon of sand- and silt-size [[Char (chemistry)|char]] particles of both wood and herb origin<ref>{{cite journal |last1=Ponomarenko |first1=Elena V. |last2=Anderson |first2=Darwin W. |date=August 2001 |title=Importance of charred organic matter in Black Chernozem soils of Saskatchewan |journal=[[Canadian Journal of Soil Science]] |language=en |volume=81 |issue=3 |pages=285–97 |doi=10.4141/S00-075 |issn=1918-1841 |doi-access=free }}</ref> attests for previously forested environments which humans destroyed by fire for the sake of [[agriculture]] or [[hunting]] of large herbivores after the [[Last Glacial Period]].<ref>{{cite journal |last1=Vysloužilová |first1=Barbora |last2=Danková |first2=Lenka |last3=Ertlen |first3=Damien |last4=Novák |first4=Jan |last5=Schwartz |first5=Dominique |last6=Šefrna |first6=Luděk |last7=Delhon |first7=Claire |last8=Berger |first8=Jean-François |date=18 February 2014 |title=Vegetation history of chernozems in the Czech Republic |journal=Vegetation History and Archaeobotany |language=en |volume=23 |issue=Suppl. 1 |pages=97–108 |doi=10.1007/s00334-014-0441-7 |issn=1617-6278 |url=https://www.researchgate.net/publication/260262558 |access-date=23 January 2026 }}</ref> Whether charcoal was deliberately managed by humans as a [[soil conditioner]] and whether [[earthworm]] grinding and mixing of charcoal contributed to the formation of [[Temperate climate|temperate]] Dark Earths is still a matter of conjecture, although it has been claimed that [[Prehistory|Prehistoric]] agriculture favored earthworm abundance for Chernozem formation.<ref>{{cite journal |last1=Dreibrodt |first1=Stefan |last2=Hofmann |first2=Robert |last3=Dal Corso |first3=Marta |last4=Bork |first4=Hans-Rudolf |last5=Duttmann |first5=Rainer |last6=Martini |first6=Sarah |last7=Saggau |first7=Philipp |last8=Schwark |first8=Lorenz |last9=Shatilo |first9=Lyudmila |last10=Videiko |first10=Michail |last11=Nadeau |first11=Marie-Josée |last12=Grootes |first12=Pieter Meiert |last13=Kirleis |first13=Wiebke |last14=Müller |first14=Johannes |date=1 March 2022 |title=Earthworms, Darwin and prehistoric agriculture: Chernozem genesis reconsidered |journal=Geoderma |language=en |volume=409 |article-number=115607 |doi=10.1016/j.geoderma.2021.115607 |issn=0016-7061 |url=https://www.academia.edu/66392628 |access-date=23 January 2026 |hdl=11250/2978117 |hdl-access=free }}</ref>
== Humans and soil ==
[[Albert Howard]] is credited as the first [[Western world|Westerner]] to publish Native techniques of [[sustainable agriculture]]. As noted by Howard in 1945, "In all future studies of disease we must, therefore, always begin with the soil. This must be gotten into good condition first of all and then the reaction of the soil, the plant, animal, and man observed. Many diseases will then automatically disappear... Soil fertility is the basis of the public health system of the future...". Howard connects the health crises of crops to the impacts of [[livestock]] and [[human health]], ultimately spreading the message that humans must respect and restore the soil for the benefit of the human and non-human world. He continues that [[industrial agriculture]] disrupts the delicate [[balance of nature]] and irrevocably robs the soil of its fertility.<ref>{{cite book |last=Howard |first=Albert |title=Farming and gardening for health or disease |publisher=[[Faber & Faber]] |location=London, United Kingdom |year=1945 |url=https://z-library.sk/book/120742402/3e5c15 |access-date=23 January 2026 }}</ref>
== Irrigation effects ==
[[Irrigation]] is a process by which crops are watered by man-made means, such as bringing in water from pipes, [[canal]]s, or [[Irrigation sprinkler|sprinklers]]. Irrigation is used when the natural [[rainfall]] patterns of a region are not sustainable enough to maintain crops. Ancient civilizations heavily relied on irrigation and today about 18% of the world's cropland is irrigated.<ref>{{cite web |last=Stanley |first=Morgan |date=9 December 2024 |title=Irrigation |url=https://education.nationalgeographic.org/resource/irrigation |access-date=23 January 2026 |website=education.nationalgeographic.org |language=en }}</ref> The quality of irrigation water is very important to maintain soil fertility and [[tilth]], and for using more soil depth by the plants.<ref>{{cite web |last1=Whiting |first1=David |last2=Card |first2=Adrian |last3=Reeder |first3=Jean |last4=Wilson |first4=Carl |last5=Blunt |first5=Tamla |date=July 2023 |title=Managing soil tilth: texture, structure, and pore space |url=https://extension.colostate.edu/resource/managing-soil-tilth-texture-structure-and-pore-space/ |access-date=23 January 2026 |website=[[Colorado State University]] |language=en }}</ref> When soil is irrigated with high [[Alkali|alkaline]] water, unwanted [[sodium salt]]s build up in the soil which would make soil draining capacity very poor.<ref>{{cite journal |last1=He |first1=Yangbo |last2=DeSutter |first2=Thomas |last3=Casey |first3=Frank |last4=Clay |first4=David |last5=Franzen |first5=Dave |last6=Steele |first6=Dean |date=May 2015 |title=Field capacity water as influenced by Na and EC: implications for subsurface drainage |journal=Geoderma |language=en |volume=245–246 |pages=83–8 |doi=10.1016/j.geoderma.2015.01.020 |issn=0016-7061 |url=https://www.academia.edu/125082799 |access-date=23 January 2026 }}</ref> So plant roots cannot penetrate deep into the soil for optimum growth in [[Alkali soils]].<ref>{{cite journal |last1=Adcock |first1=Damien |last2=McNeill |first2=Ann M. |last3=McDonald |first3=Glenn K. |last4=Armstrong |first4=Roger D. |date=18 October 2007 |title=Subsoil constraints to crop production on neutral and alkaline soils in south-eastern Australia: a review of current knowledge and management strategies |journal=Australian Journal of Experimental Agriculture |language=en |volume=47 |issue=11 |pages=1245–61 |doi=10.1071/EA06250 |issn=1446-5574 |url=https://www.researchgate.net/publication/240507778 |access-date=23 January 2026 }}</ref> When soil is [[Environmental impact of irrigation|irrigated with low pH (acidic) water]], the useful salts (Ca, Mg, K, P, S, etc.) are removed by draining water from the [[Soil pH|acidic soil]] and in addition plant-unwanted [[aluminium]] and [[manganese]] salts are dissolved from the soil, impeding plant growth.<ref>{{cite web |last1=Hopkins |first1=Bryan G. |last2=Horneck |first2=Donald A. |last3=Stevens |first3=Robert G. |last4=Ellsworth |first4=Jason W. |last5=Sullivan |first5=Dan M. |date=August 2007 |title=Managing irrigation water quality for crop production in the Pacific Northwest |url=https://ir.library.oregonstate.edu/downloads/m039k511n |access-date=23 January 2026 |website=[[Oregon State University]] |language=en }}</ref> When soil is irrigated with high [[salinity]] water or sufficient water is not draining out from the irrigated soil, the soil would convert into [[Soil salinity control|saline soil]] and lose its fertility.<ref>{{cite journal |last1=Shehzad |first1=Imran |last2=Sarwar |first2=Gulam |last3=Manzoor |first3=Muhammad Zeeshan |last4=Zafar |first4=Ayesha |last5=Muhammad |first5=Sher |last6=Murtaza |first6=Ghulam |date=27 July 2020 |title=Effect of saline water irrigation on chemical properties and fertility status of soil |journal=Pakistan Journal of Agricultural Research |language=en |volume=33 |issue=3 |pages=527–34 |doi=10.17582/journal.pjar/2020/33.3.527.534 |issn=2227-8311 |doi-access=free }}</ref> Saline water enhances the [[turgor pressure]] or [[osmotic pressure]] requirement which impedes the uptake of water and nutrients by the plant roots.<ref>{{cite journal |last=Steudle |first=Ernst |date=September 2000 |title=Water uptake by plant roots: an integration of views |journal=[[Plant and Soil]] |language=en |volume=226 |pages=45–56 |doi=10.1023/A:1026439226716 |issn=1573-5036 |url=https://web.archive.org/web/20070728205854id_/http://www.homepage.steudle.uni-bayreuth.de/papers/2000/fulltext.pdf |access-date=26 January 2026 }}</ref>
[[Topsoil]] loss takes place in [[alkali soil]]s due to erosion by rainwater [[surface runoff]] or drainage<ref>{{cite journal |last1=Wang |first1=Xinyi |last2=Zhu |first2=Hui |last3=Shutes |first3=Brian |last4=Yan |first4=Baixing |last5=Lyu |first5=Jiao |last6=Zhang |first6=Fuman |date=21 August 2023 |title=Nutrient runoff loss from saline-alkali paddy fields in Songnen Plain of Northeast China via different runoff pathways: effects of nitrogen fertilizer types |journal=Environmental Science and Pollution Research |language=en |volume=30 |issue=43 |pages=97977–89 |doi=10.1007/s11356-023-29314-x |issn=1614-7499 |url=https://www.researchgate.net/publication/373262230 |access-date=26 January 2026 }}</ref> as they form [[colloid]]s (fine mud) in contact with water.<ref>{{cite journal |last1=Liu |first1=Zhiguo |last2=Xu |first2=Fengjie |last3=Zu |first3=Yuangang |last4=Meng |first4=Ronghua |last5=Wang |first5=Wenjie |date=June 2016 |title=Study on water-dispersible colloids in saline–alkali soils by atomic force microscopy and spectrometric methods |journal=[[Microscopy Research and Technique]] |language=en |volume=79 |issue=6 |pages=525–31 |doi=10.1002/jemt.22662 |issn=1097-0029 |url=https://www.researchgate.net/publication/301218006 |access-date=26 January 2026 }}</ref> Plants absorb water-soluble inorganic salts mostly from the soil for their growth, although some non-neglectable uptake occurs also from rain and aerial spray deposited on the foliage.<ref>{{cite journal |last=Kannan |first=Seshadri |date=December 1986 |title=Physiology of foliar uptake of inorganic nutrients |journal=[[Proceedings of the Indian Academy of Sciences]] |language=en |volume=96 |issue=6 |pages=457–70 |doi=10.1007/BF03053540 |issn=2454-9983 |url=https://z-library.sk/book/39009616/2ea8f5 |access-date=26 January 2026 }}</ref> Soil as such does not lose fertility just by growing crops if [[weathering]] of soil minerals compensate for nutrients exported in [[harvest]].<ref>{{cite journal |last1=Vadeboncoeur |first1=Matthew A. |last2=Hamburg |first2=Steven P. |last3=Yanai |first3=Ruth D. |last4=Blum |first4=Joel D. |date=15 April 2014 |title=Rates of sustainable forest harvest depend on rotation length and weathering of soil minerals |journal=[[Forest Ecology and Management]] |language=en |volume=318 |pages=194–205 |doi=10.1016/j.foreco.2014.01.012 |issn=1872-7042 |url=https://www.academia.edu/82265652 |access-date=26 January 2026 }}</ref> However, it can lose its fertility through the accumulation of unwanted and depletion of wanted inorganic salts by improper irrigation<ref>{{cite book |last1=Kovda |first1=Victor A. |chapter=Arid land irrigation and soil fertility: problems of salinity, alkalinity, compaction |title=Arid land irrigation in developing countries: environmental problems and effects |year=1977 |editor-last=Worthington |editor-first=E. Barton |publisher=[[Pergamon Press]] |location=Oxford, United Kingdom |pages=211–35 |chapter-url=https://z-library.sk/book/69348218/43bbe3 |access-date=22 January 2026 }}</ref> and [[acid rain]] water.<ref>{{cite journal |last1=Singh |first1=Anita |last2=Agrawal |first2=Madhoolika |date=February 2008 |title=Acid rain and its ecological consequences |journal=[[Journal of Environmental Biology]] |language=en |volume=29 |issue=1 |pages=15–24 |issn=2394-0379 |url=https://www.researchgate.net/publication/23295957 |access-date=26 January 2026 }}</ref> The fertility of many soils which are not suitable for plant growth can be enhanced many times gradually by providing adequate irrigation water of suitable quality<ref>{{cite journal |last1=Nikolskii |first1=Yuri N. |last2=Aidarov |first2=Ivan P. |last3=Landeros-Sánchez |first3=Cesáreo |last4=Pchyolkin |first4=Viktor V. |date=13 November 2019 |title=Impact of long-term freshwater irrigation on soil fertility |journal=Irrigation and Drainage |language=en |volume=68 |issue=5 |pages=993–1001 |doi=10.1002/ird.2381 |issn=1531-0361 |url=https://z-lib.fm/book/108876940/8bbfda |access-date=26 January 2026 }}</ref> and good drainage from the soil.<ref>{{cite journal |last1=Mekonen |first1=Meles |last2=Tesfaye |first2=Kindie |last3=Bayu |first3=Wondimu |year=2013 |title=Soil drainage and nutrient management to improve productivity of waterlogged vertisols for small-scale farmers |journal=Engineering International |language=en |volume=1 |issue=2 |pages=27–39 |issn=2409-3629 |url=https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3139326 |access-date=26 January 2026 }}</ref>
==Global distribution== [[Image:Global soils map USDA.jpg|thumb|600px|center|Global distribution of soil types of the [[USDA soil taxonomy]] system. [[Mollisols]], shown here in dark green, are a good (though not the only) indicator of high soil fertility. They coincide to a large extent with the world's major grain producing areas like the North American [[Prairie]] States, the [[Pampa]] and [[Gran Chaco]] of South America and the [[Ukraine]]-to-Central Asia [[Chernozem|Black Earth]] belt.]]
==See also== * [[Arable land]] * [[Plaggen soil]] * [[Shifting cultivation]] * [[Soil contamination]] * [[Soil life]] * [[Terra preta]] * [[Cation-exchange capacity]]
==References== {{Reflist}}
{{Soil science topics}} {{Plant nutrition}} {{Natural resources}} {{Authority control}}
[[Category:Soil fertility]] [[Category:Soil improvers]] [[Category:Fertilizers]] [[Category:Horticulture]]