Editing Humus (section)

{{Short description|Organic matter in soils resulting from decay of plant and animal materials}}
{{About|the organic matter in soil|the food|Hummus|the band|Humus (band)}}
{{Use dmy dates|date=December 2024}}
[[File:Soil Horizons.svg|thumb|Humus has a characteristic black or dark brown color and is an accumulation of organic [[Soil carbon|carbon]]. Besides the three major soil horizons of (A) surface/topsoil, (B) [[subsoil]], and (C) substratum, some soils have an organic horizon (O) on the very surface. Hard bedrock (R) is not in a strict sense soil.
]]
In classical<ref>
{{citation
|title= A soil-science revolution upends plans to fight climate change
|last=Popkin
|first=Gabriel
|date=27 July 2021
|url=https://www.quantamagazine.org/a-soil-science-revolution-upends-plans-to-fight-climate-change-20210727/
|publisher=[[Quanta Magazine]]
|access-date=9 June 2024
|quote="The latest edition of The Nature and Properties of Soils, published in 2016, cites Lehmann’s 2015 paper and acknowledges that "our understanding of the nature and genesis of soil humus has advanced greatly since the turn of the century, requiring that some long-accepted concepts be revised or abandoned".}}
</ref> [[soil science]], '''humus''' is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of [[soil organic matter]]. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground".<ref>{{cite web |title=Humus |url=https://www.dictionary.com/browse/humus |access-date=9 June 2024 |via=[[Dictionary.com]] ''Random House Dictionary Unabridged''}}</ref>

In [[agriculture]], "humus" sometimes also is used to describe mature or natural [[compost]] extracted from a woodland or other spontaneous source for use as a [[soil conditioner]].<ref>{{cite encyclopedia |title=Humus |encyclopedia=[[Encyclopaedia Britannica]] Online |date=2011 |access-date=9 June 2024 |url=https://www.britannica.com/EBchecked/topic/276408/humus }}</ref> It is also used to describe a [[topsoil]] [[Soil horizon|horizon]] that contains [[organic matter]] (''humus type'',<ref>{{cite journal |last1=Chertov |first1=Oleg G. |last2=Komarov |first2=Alexander S. |last3=Crocker |first3=Graham |last4=Grace |first4=Peter |last5=Klir |first5=Jan |last6=Körschens |first6=Martin |last7=Poulton |first7=Paul R. |last8=Richter |first8=Daniel |date=1997 |title=Simulating trends of soil organic carbon in seven long-term experiments using the SOMM model of the humus types |journal=Geoderma |volume=81 |issue=1–2 |pages=121–135 |doi=10.1016/S0016-7061(97)00085-2 |bibcode=1997Geode..81..121C |url=https://fr.articles.sk/book/17536355/c35523 |access-date=9 June 2024 }}</ref> ''humus form'',<ref>{{cite journal |last1=Brêthes |first1=Alain |last2=Brun |first2=Jean-Jacques |last3=Jabiol |first3=Bernard |last4=Ponge |first4=Jean-François |last5=Toutain |first5=François |date=1995 |title=Classification of forest humus forms: a French proposal |journal=Annales des Sciences Forestières |volume=52 |issue=6 |pages=535–46 |doi=10.1051/forest:19950602 |url=https://www.researchgate.net/publication/45341270 |access-date=16 June 2024 }}</ref> or ''humus profile''<ref>{{cite journal |last=Bernier |first=Nicolas |date=1998 |title=Earthworm feeding activity and development of the humus profile |journal=Biology and Fertility of Soils |volume=26 |issue=3 |pages=215–23 |doi=10.1007/s003740050370 |bibcode=1998BioFS..26..215B |url=https://www.academia.edu/34816078 |access-date=16 June 2024 }}</ref>).

Humus has many [[nutrient]]s that improve the health of soil, [[nitrogen]] being the most important. The ratio of [[carbon]] to [[nitrogen]] ([[C：N ratio|C:N]]) of humus commonly ranges between 8:1 and 15:1 with the median being about 12:1.<ref>{{cite book |last=Brady |first=Nyle C. |title=The nature and properties of soils |url=https://www.academia.edu/23641831 |date=1984 |edition=9th |publisher=[[Macmillan Publishing Company]] |location=New York, New York |language=en |isbn=978-0029460306 |page=269 |access-date=1 September 2024 }}</ref> It also significantly improves (decreases) the [[bulk density]] of soil.<ref>{{cite journal |last1=Bauer |first1=Armand |year=1974 |title=Influence of soil organic matter on bulk density and available water capacity of soils |journal=Farm Research |volume=31 |issue=5 |pages=44–52 |url=https://library.ndsu.edu/ir/bitstream/handle/10365/24299/ndfr_19740501_v31_iss05_044.pdf |access-date=23 June 2024 }}</ref> Humus is [[Amorphous solid|amorphous]] and lacks the cellular structure characteristic of [[organism]]s.<ref name="Whitehead1963">{{cite journal |last1=Whitehead |first1=D. C. |last2=Tinsley |first2=J. |date=1963 |title=The biochemistry of humus formation |journal=[[Journal of the Science of Food and Agriculture]] |volume=14 |issue=12 |pages=849–57 |doi=10.1002/jsfa.2740141201 |bibcode=1963JSFA...14..849W |url=https://fr.articles.sk/book/1689524/861585 |access-date=23 June 2024 }}</ref>

The [[Biosolids|solid]] residue of [[sewage sludge treatment]], which is a secondary phase in the [[wastewater treatment]] process, is also called humus.<ref>{{cite web |title=Sewage treatment |url=https://library.e.abb.com/public/19d4b5f59e87bdd9c12569580054d17e/3_sewage.pdf |access-date=30 June 2024 }}</ref> When not judged [[Contamination|contaminated]] by [[pathogen]]s, toxic [[heavy metals]], or [[persistent organic pollutant]]s according to standard tolerance levels, it is sometimes [[compost]]ed and used as a [[fertilizer|soil amendment]].<ref>{{cite web |url=https://compost.css.cornell.edu/Brinton.pdf |title=Compost quality standards and guidelines, final report |year=2020 |publisher=[[Cornell University]] |location=Ithaca, New York |last=Brinton |first=William F.  |access-date=7 July 2024 }}</ref>