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Humus

This article is about the organic matter in soil. For the food, see Hummus. For the band, see Humus (band).

Humus has a characteristic black or dark brown color and is an accumulation of organic 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[1] 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".[2]

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.[3] It is also used to describe a topsoil horizon that contains organic matter (humus type,[4] humus form,[5] or humus profile[6]).

Humus has many nutrients that improve the health of soil, nitrogen being the most important. The ratio of carbon to nitrogen (C:N) of humus commonly ranges between 8:1 and 15:1 with the median being about 12:1.[7] It also significantly improves (decreases) the bulk density of soil.[8] Humus is amorphous and lacks the cellular structure characteristic of organisms.[9]

The solid residue of sewage sludge treatment, which is a secondary phase in the wastewater treatment process, is also called humus.[10] When not judged contaminated by pathogens, toxic heavy metals, or persistent organic pollutants according to standard tolerance levels, it is sometimes composted and used as a soil amendment.[11]

  1. ^ Popkin, Gabriel (27 July 2021), A soil-science revolution upends plans to fight climate change, Quanta Magazine, retrieved 9 June 2024, "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."
  2. ^ "Humus". Retrieved 9 June 2024 – via Dictionary.com Random House Dictionary Unabridged.
  3. ^ "Humus". Encyclopaedia Britannica Online. 2011. Retrieved 9 June 2024.
  4. ^ Chertov, Oleg G.; Komarov, Alexander S.; Crocker, Graham; Grace, Peter; Klir, Jan; Körschens, Martin; Poulton, Paul R.; Richter, Daniel (1997). "Simulating trends of soil organic carbon in seven long-term experiments using the SOMM model of the humus types". Geoderma. 81 (1–2): 121–135. Bibcode:1997Geode..81..121C. doi:10.1016/S0016-7061(97)00085-2. Retrieved 9 June 2024.
  5. ^ Brêthes, Alain; Brun, Jean-Jacques; Jabiol, Bernard; Ponge, Jean-François; Toutain, François (1995). "Classification of forest humus forms: a French proposal". Annales des Sciences Forestières. 52 (6): 535–46. doi:10.1051/forest:19950602. Retrieved 16 June 2024.
  6. ^ Bernier, Nicolas (1998). "Earthworm feeding activity and development of the humus profile". Biology and Fertility of Soils. 26 (3): 215–23. Bibcode:1998BioFS..26..215B. doi:10.1007/s003740050370. Retrieved 16 June 2024.
  7. ^ Brady, Nyle C. (1984). The nature and properties of soils (9th ed.). New York, New York: Macmillan Publishing Company. p. 269. ISBN 978-0029460306. Retrieved 1 September 2024.
  8. ^ Bauer, Armand (1974). "Influence of soil organic matter on bulk density and available water capacity of soils" (PDF). Farm Research. 31 (5): 44–52. Retrieved 23 June 2024.
  9. ^ Whitehead, D. C.; Tinsley, J. (1963). "The biochemistry of humus formation". Journal of the Science of Food and Agriculture. 14 (12): 849–57. Bibcode:1963JSFA...14..849W. doi:10.1002/jsfa.2740141201. Retrieved 23 June 2024.
  10. ^ "Sewage treatment" (PDF). Retrieved 30 June 2024.
  11. ^ Brinton, William F. (2020). "Compost quality standards and guidelines, final report" (PDF). Cornell University. Ithaca, New York. Retrieved 7 July 2024.

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