Editing Humus (section)

==Benefits of soil organic matter and humus==

The importance of chemically stable humus is thought by some to be the [[Soil fertility|fertility]] it provides to soils in both a physical and chemical sense,<ref>{{cite journal |last1=Hargitai |first1=László |date=December 1993 |title=The role of organic matter content and humus quality in the maintenance of soil fertility and in environmental protection |journal=[[Landscape and Urban Planning]] |volume=27 |issue=2–4 |pages=161–67 |doi=10.1016/0169-2046(93)90044-E |bibcode=1993LUrbP..27..161H |url=https://fr.articles.sk/book/19958903/07e3a6 |access-date=27 October 2024 }}</ref> though some agricultural experts put a greater focus on other features of it, such as its ability to suppress disease.<ref>{{cite journal |last1=Hoitink |first1=Harry A. J. |last2=Fahy |first2=Peter C. |date=September 1986 |title=Basis for the control of soilborne plant pathogens with composts |journal=[[Annual Review of Phytopathology]] |volume=24 |pages=93–114 |doi=10.1146/annurev.py.24.090186.000521 |url=https://fr.articles.sk/book/18744629/4076fa |access-date=27 October 2024 }}</ref> It helps the soil retain moisture<ref>{{cite journal |last=Lal |first1=Rattan |date=September 2020 |title=Soil organic matter and water retention |journal=[[Agronomy Journal]] |volume=116 |issue=5 |pages=3265–77 |doi=10.1002/agj2.20282 |url=https://www.researchgate.net/publication/341213360 |access-date=27 October 2024 }}</ref> by increasing [[Porosity|microporosity]]<ref>{{cite journal |last1=de Macedo |first1=José Ronaldo |last2=do Amaral Meneguelli |first2=Neli |last3=Ottoni Filho |first3=Theophilo Benedicto |last4=Lima |first4=Jorge Araújo de Sousa |date=February 2007 |title=Estimation of field capacity and moisture retention based on regression analysis involving chemical and physical properties in Alfisols and Ultisols of the state of Rio de Janeiro |journal=Communications in Soil Science and Plant Analysis |volume=33 |issue=13–14 |pages=2037–55 |doi=10.1081/CSS-120005747 |bibcode=2002CSSPA..33.2037D |s2cid=98466747 |url=https://fr.articles.sk/book/32902177/18be8b |access-date=27 October 2024 }}</ref> and encourages the formation of good [[soil structure]].<ref>{{cite journal |last1=Hempfling |first1=Reinhold |last2=Schulten |first2=Hans-Rolf |last3=Horn |first3=Rainer |date=June 1990 |title=Relevance of humus composition to the physical/mechanical stability of agricultural soils: a study by direct pyrolysis-mass spectrometry |journal=Journal of Analytical and Applied Pyrolysis |volume=17 |issue=3 |pages=275–81 |doi=10.1016/0165-2370(90)85016-G |url=https://fr.articles.sk/book/8543777/01704b |access-date=3 November 2024 }}</ref><ref>{{cite book |date=1996 |title=Humic substances in terrestrial ecosystems |editor-last=Piccolo |editor-first=Alessandro |pages=225–64 |chapter=Humus and soil conservation |last=Piccolo |first=Alessandro |doi=10.1016/B978-044481516-3/50006-2 |isbn=978-0-444-81516-3 |publisher=[[Elsevier]] |location=Amsterdam, The Netherlands |url=https://www.researchgate.net/publication/281451183 |access-date=3 November 2024 }}</ref> The incorporation of [[oxygen]] into large organic molecular assemblages generates many active, negatively charged sites that bind to positively charged [[ion]]s (cations) of [[Plant nutrition|plant nutrients]], making them more available to the plant by way of [[ion exchange]].<ref name="Szalay-1964">{{cite journal |last=Szalay |first1=Alex |date=October–November 1964 |title=Cation exchange properties of humic acids and their importance in the geochemical enrichment of UO2++ and other cations |journal=[[Geochimica et Cosmochimica Acta]] |volume=28 |issue=10–11 |pages=1605–14 |doi=10.1016/0016-7037(64)90009-2 |bibcode=1964GeCoA..28.1605S |url=https://fr.articles.sk/book/19639940/3bac09 |access-date=3 November 2024 }}</ref> Humus allows soil organisms to feed and reproduce and is often described as the "life-force" of the soil.<ref name="ReferenceA">{{cite journal |last1=Elo |first1=Seija |last2=Maunuksela |first2=Liisa |last3=Salkinoja-Salonen |first3=Mirja |last4=Smolander |first4=Aino |last5=Haahtela |first5=Kielo |date=February 2000 |title=Humus bacteria of Norway spruce stands: plant growth promoting properties and birch, red fescue and alder colonizing capacity |journal=[[FEMS Microbiology Ecology]] |volume=31 |issue=2 |pages=143–52 |doi=10.1111/j.1574-6941.2000.tb00679.x |pmid=10640667 |doi-access=free }}</ref><ref name="Vreeken-Buijs-1998">{{cite journal |last1=Vreeken-Buijs |first1=Madelein J. |last2=Hassink |first2=Jan |last3=Brussaard |first3=Lijbert |date=1998 |title=Relationships of soil microarthropod biomass with organic matter and pore size distribution in soils under different land use |journal=[[Soil Biology and Biochemistry]] |volume=30 |issue=1 |pages=97–106 |doi=10.1016/S0038-0717(97)00064-3|bibcode=1998SBiBi..30...97V |url=https://www.academia.edu/65368490 |access-date=3 November 2024 }}</ref>

* The process that converts soil organic matter into humus feeds the population of microorganisms and other creatures in the soil, and thus maintains high and healthy levels of soil life.<ref name="ReferenceA"/><ref name="Vreeken-Buijs-1998"/>
* The rate at which soil organic matter is converted into humus promotes (when fast, e.g. [[humus form|mull]]) or limits (when slow, e.g. [[mor humus|mor]]) the coexistence of plants, animals, and microorganisms in the soil.<ref name="Ponge2003">{{cite journal |last=Ponge |first=Jean-François |date=July 2003 |title=Humus forms in terrestrial ecosystems: a framework to biodiversity |journal=[[Soil Biology and Biochemistry]] |volume=35 |issue=7 |pages=935–45|doi=10.1016/S0038-0717(03)00149-4  |url=https://www.academia.edu/20508983 |access-date=10 November 2024 }}</ref>
* "Effective humus" and "stable humus" are additional sources of nutrients for microbes: the former provides a readily available supply, and the latter acts as a long-term storage reservoir.<ref>{{cite book |date=1991 |title=Advances in soil organic matter research: the impact on agriculture and the environment |editor-last=Wilson |editor-first=W. S. |pages=355–64 |chapter=Soil organic matter: its central position in organic farming |last=Hodges |first=R. D. |doi=10.1016/b978-1-85573-813-3.50040-8 |isbn=978-1-85573-813-3 |publisher=[[Woodhead Publishing]] |location=Sawston, United Kingdom |url=https://fr.articles.sk/book/81383430/4b29a3 |access-date=10 November 2024 }}</ref>
* Decomposition of dead plant material causes complex organic compounds to be slowly oxidized ([[lignin]]-like humus) or to decompose into simpler forms ([[sugar]]s and [[amino sugar]]s, and [[Aliphatic compound|aliphatic]] and [[Naturally occurring phenols|phenolic]] [[organic acid]]s), which are further transformed into microbial biomass (microbial humus) or reorganized and further oxidized into humic assemblages ([[fulvic acid]]s and [[humic acid]]s), which bind to [[clay minerals]] and [[metal hydroxide]]s.<ref>{{cite journal |last1=Gunina |first1=Anna |last2=Kuzyakov |first2=Yakov |date=April 2022 |title=From energy to (soil organic) matter |journal=[[Global Change Biology]] |volume=28 |issue=7 |pages=2169–82 |doi=10.1111/gcb.16071 |doi-access=free }}</ref> The ability of plants to absorb humic substances with their roots and [[Metabolism|metabolize]] them has been long debated.<ref>{{cite journal |last1=Senn |first1=T. L. |last2=Kingman |first2=Alta R. |last3=Godley |first3=W. C. |date=1973 |title=A review of humus and humic acids |url=https://www.humintech.com/fileadmin/content_images/agriculture/information/articles_pdf/A-Review-of-Humus-and-Humic-Acids_T.L.Senn__A.R.Kingsmann.pdf |journal=Research Series, South Carolina Agricultural Experiment Station |volume=145 |access-date=24 November 2024 }}</ref> There is now a consensus that humus functions [[Plant hormone|hormonally]] rather than simply [[Plant nutrition|nutritionally]] in [[plant physiology]],<ref>{{cite journal |last1=Eyheraguibel |first1=Boris |last2=Silvestre |first2=Jérôme |last3=Morard |first3=Philippe |date=July 2008 |title=Effects of humic substances derived from organic waste enhancement on the growth and mineral nutrition of maize |url=https://hal.science/hal-00940093/file/Eyheraguibel_10804.pdf |journal=[[Bioresource Technology]] |volume=99 |issue=10 |pages=4206–12 |doi=10.1016/j.biortech.2007.08.082 |pmid=17962015 |bibcode=2008BiTec..99.4206E |access-date=17 November 2024 }}</ref><ref>{{cite journal |last1=Zandonadi |first1=Daniel Basilio |last2=Santos |first2=Mirella Pupo |last3=Busato |first3=Jader Galba |last4=Peres |first4=Lázaro Eustáquio Pereira |last5=Façanha |first5=Arnoldo Rocha |title=Plant physiology as affected by humified organic matter |journal=Theoretical and Experimental Plant Physiology |date=2013 |volume=25 |issue=1 |pages=12–25 |doi=10.1590/S2197-00252013000100003 |doi-access=free }}</ref> and that organic sunstances exuded by roots and transformed in humus by soil organisms are an evolved strategy by which plants "talk" to the soil.<ref>{{cite journal |last1=Nardi |first1=Serenella |last2=Ertani |first2=Andrea |last3=Francioso |first3=Ornella |date=February 2017 |title=Soil–root cross-talking: the role of humic substances |journal=Journal of Plant Nutrition and Soil Science |volume=180 |issue=1 |pages=5–13 |doi=10.1002/jpln.201600348 |url=https://www.academia.edu/102119488 |access-date=17 November 2024 |hdl=2318/1731194 |hdl-access=free }}</ref>
* Humus is a negatively [[Electric charge|charged]] [[colloid]]al substance which increases the [[cation-exchange capacity]] of soil, hence its ability to store nutrients by [[chelation]].<ref>{{cite journal |last1=Shoba |first1=V. N. |last2=Chudnenko |first2=Konstantin V. |date=August 2014 |title=Ion exchange properties of humus acids |journal=Eurasian Soil Science |volume=47 |issue=8 |pages=761–71 |doi=10.1134/S1064229314080110 |url=https://www.researchgate.net/publication/269385340 |access-date=24 November 2024 }}</ref> While these nutrient cations are available to plants, they are held in the soil and prevented from being leached by rain or irrigation.<ref name="Szalay-1964"/>
* Humus can hold the equivalent of 80–90% of its weight in moisture and therefore increases the soil's capacity to withstand drought.<ref>{{cite journal |last1=Olness |first1=Alan |last2=Archer |first2=David |date=February 2005 |title=Effect of organic carbon on available water in soil |journal=Soil Science |volume=170 |issue=2 |pages=90–101 |doi=10.1097/00010694-200502000-00002 |bibcode=2005SoilS.170...90O |s2cid=95336837 |url=https://fr.articles.sk/book/54264627/14eda9 |access-date=24 November 2024 }}</ref>
* The biochemical structure of humus enables it to moderate, i.e. buffer, excessive [[Soil pH|acidic]] or [[Alkali soil|alkaline]] soil conditions.<ref>{{cite journal |last1=Kikuchi |first1=Ryunosuke |date=February 2004 |title=Deacidification effect of the litter layer on forest soil during snowmelt runoff: laboratory experiment and its basic formularization for simulation modeling |journal=[[Chemosphere (journal)|Chemosphere]] |volume=54 |issue=8 |pages=1163–69 |doi=10.1016/j.chemosphere.2003.10.025 |pmid=14664845 |bibcode=2004Chmsp..54.1163K |url=https://fr.articles.sk/book/16655436/acdc92 |access-date=24 November 2024 }}</ref>
* During humification, microbes secrete sticky, gum-like [[mucilage]]s; these contribute to the crumby structure ([[tilth]]) of the soil by adhering particles together and allowing greater [[Aeration#Aeration of soil|aeration]] of the soil.<ref>{{cite journal |last1=Caesar-Tonthat |first1=Thecan C. |date=August 2002 |title=Soil binding properties of mucilage produced by a basidiomycete fungus in a model system |url=https://fr.articles.sk/book/20537646/09bc94 |journal=[[Mycological Research]] |volume=106 |issue=8 |pages=930–37 |doi=10.1017/S0953756202006330 |access-date=24 November 2024 }}</ref> Toxic substances such as [[Heavy metal (chemistry)|heavy metals]] and excess nutrients can be chelated, i.e., bound to the organic molecules of humus, and so prevented from leaching away.<ref>{{cite journal |last1=Zhu |first1=Rui |last2=Wu |first2=Min |last3=Yang |first3=Jian |date=February 2011 |title=Mobilities and leachabilities of heavy metals in sludge with humus soil |journal=Journal of Environmental Sciences |volume=23 |issue=2 |pages=247–54 |doi=10.1016/S1001-0742(10)60399-3 |url=https://fr.articles.sk/book/14270592/0155c3 |access-date=24 November 2024 }}</ref>
* The dark, usually brown or black, color of humus helps to warm cold soils in spring.<ref>{{cite journal |last1=Ludwig |first1=J. W. |last2=Harper |first2=John L. |date=July 1958 |title=The influence of the environment on seed and seedling mortality. VIII. The influence of soil colour |journal=[[Journal of Ecology]] |volume=46 |issue=2 |pages=381–89 |doi=10.2307/2257402 |url=https://fr.articles.sk/book/57099612/546f22 |access-date=1 December 2024 }}</ref>
*Humus can contribute to [[climate change mitigation]] through its [[carbon sequestration]] potential.<ref>{{cite journal |last1=Amelung |first1=Wulf| last2=Bossio |first2=Deborah |last3=De Vries |first3=Wim |last4=Kögel-Knabner |first4=Ingrid |author4-link=Ingrid Kögel-Knabner|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=Budiman |last12=Pan |first12=Gen-Xing |last13=Paustian |first13=Keith |last14=Rumpel |first14=Cornelia |last15=Sanderman |first15=Jonathan |last16=Van Groenigen |first16=Jan Willem |last17=Mooney |first17=Sacha |last18=Van Wesemael |first18=Bas |last19=Wander |first19=Michelle |last20=Chabbi |first20=Abbad |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 |doi-access=free }}</ref> Artificial humic acid and artificial fulvic acid synthesized from agricultural litter can increase the content of dissolved organic matter and total organic carbon in soil.<ref>{{cite journal |last1=Tang |first1=Chunyu |last2=Li |first2=Yuelei |last3=Song |first3=Jingpeng |last4=Antonietti |first4=Markus |last5=Yang |first5=Fan |date=25 June 2021 |title=Artificial humic substances improve microbial activity for binding CO2 |journal=[[iScience]] |language=en |volume=24 |issue=6 |pages=102647 |doi=10.1016/j.isci.2021.102647 |pmid=34466779 |pmc=8387571 |bibcode=2021iSci...24j2647T |issn=2589-0042  |doi-access=free }}</ref>