Humus form

  1. Home
  2. Wiki

Humus form is the features of the topsoil and plant litter in a biome, such as mull humus form in deciduous forest or mor humus form in coniferous forest. Dead organic matter such as leaves decomposes into humus, and may mix with minerals, forming layers of soil. A trench through these layers is called a humus profile, and is the top part of the soil profile. A sample of the humus profile is sometimes called a humipedon.

Most soil biology occurs in humus forms.

Definitions

[edit]

Virtual Soil Science Learning Resources group: “soil horizons located at or near the surface, which have formed from organic residues (separate from or mixed with mineral particles). Horizons that may comprise a humus form include L, F, H, and Ah, but not B or C.”[1]

German Soil Science Society: “Order of distinct units defined by organic surface horizons and the first mineral horizon with similar morphology, depths and type of boundary of horizons indicating specific conditions for bioturbation, decomposition, humification, and mineralisation.”[2]

Canadian forest ministry: "a group of soil horizons located at or near the surface of a pedon, which have formed from organic residues, either separate from, or intermixed with mineral materials."[3]

History

[edit]

The most ancient contribution to the knowledge of humus forms was that of Peter Erasmus Müller, a Danish forester. In his seminal contribution Studier over Skovjord: som bidrag til skovdyrkningens theori,[4][5] later translated in German[6] and French,[7] Müller described muld (later germanized as mull) and mor, two modes of assemblage of organic and mineral matter, which he associated to two opposite classes of high and low productivity and soil fertility of Danish beechwoods. His investigations embraced a thorough analysis of plant communities, and chemical as well as microscopic investigations in various soil horizons. At the same time Charles Darwin, one year before he died, published a detailed study of the formation of mull (called by him mould, reminiscent of the Danish muld).[8] Moder was later added as a third forest humus form by F. Hartmann, midway between mull and mor and previously described as 'insect mull' by Müller.[9]

Classification

[edit]

Most classifications of humus are national (French, Belgian, German, Canadian, Russian, among many others) and do not embrace the variety of humus forms found over all world biomes, being mostly focused on forest soils and temperate climates. However HUMUSICA, a worldwide morpho-functional classification of humus forms, was created in the 2010s.[10] HUMUSICA describes and classifies humus forms from a wide array of terrestrial, semi-aquatic, cultivated and man-made environments.[11][12][13] In HUMUSICA the three current humus forms called mull, moder and mor are considered as humus systems, abbreviation of humus interaction systems, each embracing several humus forms according to variations in thickness of organic and mineral-organic horizons.[14]

Humus profiles, like soil profiles, refer to a trench through the soil. Humipedons, like pedons, refer to a column of soil. For the sake of clarity they will be synonymized, because both are made of successive layers the age of which increases with depth, more superficial layers being younger than deeper ones because organic matter is mostly deposited from above.[15] One of the key principles of humus form classifications is that humus profiles (humipedons) may evolve at a different rate from soil profiles (pedons). Given the prominent part taken by soil organisms, from bacteria to mammals, passing by plants and invertebrates, in the spatial arrangement and transformation of organic matter, humipedons display pluri-annual variations,[16] while pedon changes take decades[17] to centuries.[18] However, Walter Kubiëna considered that there was a parallelism between humus forms and soil types, hence his common classification of humus and soil profiles,[19] an opinion not shared by the majority of soil scientists who turned to soil classifications based on physical and chemical properties of more stable underlying mineral horizons, like USDA's Soil Taxonomy[20] and FAO's World Reference Base for Soil Resources (WRB).[21] It has been suggested that the pedon could be subdivided in three parts, called humipedon (for the humus profile), copedon and lithopedon, in a decreasing order of contribution of soil biological activity to their formation, and thus of their cycle of change, from decade to millennium.[22]

Diagnostic horizons

[edit]

Humipedons display a succession of horizons according to decomposition stages of fallen plant litter and its progressive incorporation to mineral matter.[23] They have been characterized on thin soil sections by soil micromorphologists,[24] but their recognition in the field is easy, being aided by the use of a hand lens if necessary.[25] They can be observed along a humus profile cut with a sharp knife along a trench[26] or be successively collected by hand one by one from the top to the bottom of a small soil monolith.[27]: 29 

OL horizon

[edit]

The OL horizon (Oi in the USDA Soil Taxonomy) is made of recognizable leaves or needles without any prominent signs of fragmentation by litter-consuming soil animals. Its colour is currently brown to black according to microbial successions taking place during the first stages of litter decomposition.[28] Bleaching of litter may also occur when leaves or needles are colonized by white-rot fungi.[29] The OL horizon is often seen permeated by fungal mycelia which penetrate leaves and needles and participate to their decomposition.[30] The OL horizon is present in all terrestrial humus forms, to the exception of the most active mull humus forms (e.g. Eumull) where it might be seasonally absent because of a fast decomposition rate of recently fallen litter.[31]

OF horizon

[edit]

The OF horizon (Oe in the USDA Soil Taxonomy) is made of fragmented leaf or needle litter, from the feeding activity of soil animals (macrofauna and mesofauna). Litter debris are mixed with feces deposited by litter-consuming animals in the form of dark-coloured pellets of a size varying from 30-50 micrometre (enchytraeids, oribatid mites, springtails) to 1-2 millimetres (epigeic earthworms, millipedes, woodlice, molluscs).[32] Enchytraeid faeces are so small that they appear as a very fine black powder covering or intermingled between decaying leaves.[23] In coniferous forests enchytraeids and some oribatid mites penetrate fallen needles once these have been heavily colonized by fungi and they deposit their feces at the inside, making them invisible if needles are not dissected by the observer.[33] In thick forest floors with active animal activity (e.g. moder humus forms) OF horizons are the seat of maximum development of the fine root system of trees and mycelia of their ectomycrorrhizal fungal associates.[34]

OH horizon

[edit]

The OH horizon (Oa in the USDA Soil Taxonomy) is the product of transformation of plant remains by soil organisms once these remains are no longer visible, but the humus thus formed is still not incorporated with mineral matter. According to the soil animals which contributed the most to the faunal activity observed in the overlying OF horizon, the OH horizon may be seen as an accumulation of still visible fecal pellets (e.g. earthworms, ants, millipedes, woodlice, crane fly larvae for macrofauna, but also oribatid mites for mesofauna) or in the case of enchytraeids as a fine powder further compacted in depth.[23] By their vertical movements[35] enchytraeids play a decisive role in the transition with the underlying A horizon.[36] Fine root systems are also present in OH horizons, together with subterranean organs of heathland plants (e.g. Ericaceae)[37] and their symbiotic fungal associates (ericoid mycorrhizae) which are able to decompose recalcitrant organic matter and transfer its nitrogen to the host plant.[38]

A horizon

[edit]

The A horizon results from the mixing of organic matter with mineral matter, mostly effected by burrowing soil animals (e.g. enchytraeids, earthworms, termites, ants, darkling beetles, gophers).[39] Some physical processes may also contribute to the mixing of organic matter with mineral matter, such as shrink-swell cycles of vertisols.[40] The A horizon is mainly made of mineral-organic aggregates (peds) of varying size, depending on the size of soil animals which excreted or moulded them in the course of their burrowing activity. Macroaggregates (> 250 µm) are built by macrofauna (e.g. earthworms, ants, termites) and megafauna (e.g. gophers), while microaggregates (< 250 µm) are built by mesofauna (e.g. enchytraeids, microarthropods.[41] Plant roots and Microorganisms (bacteria, fungi) also contribute to the formation and stabilization of aggregates through their excreta (e.g. microbial extracellular polysaccharides, root mucilages).[42][43]

E horizon

[edit]

The E horizon appears as a white or grey (ashy) horizon, the lightness (Munsell colour value) of which varies with its carbon content, always feeble.[44] Compared to the abovelying organic and mineral-organic horizons,the E horizon displays only poor signs of biological activity,[45] being mainly the seat of leaching of water, solutes (e.g. nitrates, dissolved organic carbon) and colloids (e.g. clay , humus) through a mineral layer.[46] Whether the E horizon is the main seat of mineral weathering, as suggested by the observation of pore networks of fungal origin within weathered minerals,[47] is still a matter of conjecture because highly weathered minerals are present in the E horizon.[48] This suggests that mineral weathering mainly takes place in the overlying A horizon permeated by plant roots and their microbial rhizosphere associates.[49] Like the OH horizon can be considered as the end-product of biological activity taking place in the above A horizon, the E horizon could be the end-product of biochemical processes of mineral weathering taking place in the above A horizon.

Terrestrial humus forms

[edit]

Terrestrial humus forms are found in forests, woodlands, grasslands, heathlands, steppes, tundras, deserts and semi-deserts. Five humus systems have been described in terrestrial environments: mull, moder, mor, amphi, and tangel. They have in common to have a pore space filled with air, where soil organisms are permanently or at least temporarily living.[50]

Mull

[edit]
Main article: Mull humus

Mull is the product of the mixing activity of burrowing soil animals (e.g. earthworms, ants, termites, moles, pocket gophers) which create nests and galleries within the upper part of the soil profile and excavate earth at the soil surface.[51] These disturbances allow organic matter to be in contact with mineral matter, facilitate soil aeration, create and modify ecological niches of all other soil organisms, from microbes to plant roots, passing by invertebrates. Some mull-forming animal groups ingest soil and mix it with mucus in their guts (e.g. earthworms, millipedes, termites, crane fly larvae) or mix it with their saliva to create nests and tunnels (e.g. termites). All these disturbances, whether mechanical or biochemical, stimulate microbial activity, hence faster nutrient cycles and uptake by plants. This is why mull is associated with higher fertility and productivity of ecosystems, with a positive aboveground-belowground feedback process: more nutrients for plants, better plant growth, more nutrients in plant remains, better quality of soil organic matter, better growth and reproduction of soil animals and microbes, lesser immobilization of nutrients in microbial biomass, and so on.[52]

Moder

[edit]
This section is an excerpt from Moder humus.[edit]
Moder is a forest floor type formed under mixed-wood and pure deciduous forests.[53][54] Moder is a kind of humus whose properties are the transition between mor humus and mull humus types.[55][56] Moders are similar to mors as they are made up of partially to fully humified organic components accumulated on the mineral soil. Compared to mulls, moders are zoologically active.[57] In addition, moders present as in the middle of mors and mulls with a higher decomposition capacity than mull but lower than mor.[54] Moders are characterized by a slow rate of litter decomposition by litter-dwelling organisms and fungi, leading to the accumulation of organic residues. Moder humus forms share the features of the mull and mor humus forms.[54]

Mor

[edit]
This section is an excerpt from Mor humus.[edit]
Horizon levels of Mor humus and the soil below

Mor humus is a form of forest floor humus occurring mostly in coniferous forests.[58] Mor humus consists of evergreen needles and woody debris that litter the forest floor. This litter is slow to decompose, in part due to their chemical composition (low pH, low nutrient content), but also because of the generally cool and wet conditions where mor humus is found. This results in low bacterial activity and an absence of earthworms and other soil fauna. Because of this, most of the organic matter decomposition in mor humus is carried out by fungi.

Mor humus is one of three classifications of forest floor humus, along with Moders and Mulls. Each class corresponds to a scale of increasingly colder conditions, decreasing biological diversity and activity, and decreasing nutrient availability.[59] Mor humus ranks at the bottom of this scale and is characterized by very slow decomposition and accumulation of plant material.

Tangel

[edit]

Tangel occurs in high elevation, shrub-dominated regions. It features a strongly developed “tangel layer” of brown plant remains above darker mull-like or moder humus.[19]

Climate change

[edit]

Climate change significantly affects humus forms through multiple interconnected mechanisms that alter the balance between organic matter inputs and decomposition rates. Rising temperatures accelerate microbial decomposition processes, resulting in humus depletion and a negative carbon balance in many soils.[60] Research in alpine grasslands demonstrates that a 3°C temperature increase reduces soil humus content and destabilizes soil structure.[61]

The impacts are complex and vary depending on the specific humus form type and environmental conditions. Climate warming drives predictable shifts between humus forms along temperature gradients. Research in France demonstrates that the change from Moder towards Mull occurs from north to south following increasing temperature gradients.[62]

References

[edit]
  1. ^ "Humus Forms – Forest Floors". Retrieved 2025-09-21.
  2. ^ "Glossary". Humus Form. Retrieved 2025-09-21.
  3. ^ Klinka, Karel; Green, R. N.; Trowbridge, R. L.; Lowe, L.E (1981). Taxonomic classification of humus forms in ecosystems of British Columbia: first approximation (PDF). Vancouver, British Columbia: Ministry of Forests, Province of British Columbia. Retrieved 2 September 2025.
  4. ^ Müller, Peter Erasmus (1879). "Studier over Skovjord: som bidrag til skovdyrkningens theori. I. Om bøgemuld og bøgemor på sand og ler". Tidsskrift for Skovbrug. 3: 1–124. Retrieved 2 September 2025.
  5. ^ Müller, Peter Erasmus (1884). "Studier over Skovjord: som bidrag til skovdyrkningens theori. II. Om Muld og Mor i Egeskove og paa Heder". Tidsskrift for Skovbrug. 7: 1–232. Retrieved 2 September 2025.
  6. ^ Müller, Peter Erasmus (1887). Studien über die natürlichen Humusformen und deren Einwirkung auf Vegetation und Boden. Mit analytischen Belegen von C.F.A. Tuxen. Berlin, Germany: Julius Springer. Retrieved 4 September 2025.
  7. ^ Müller, Peter Erasmus (1889). "Recherches sur les formes naturelles de l'humus et leur influence sur la végétation et le sol, traduit par Henri Grandeau". Annales de la Science Agronomique Française et Étrangère. 1: 1–351. Retrieved 4 September 2025.
  8. ^ Darwin, Charles (1881). The formation of vegetable mould through the activity of earthworms, with observations on their habits (PDF). London, United Kingdom: John Murray. Retrieved 8 September 2025.
  9. ^ Hartmann, F. (1944). "Waldhumusformen". Zeitschrift für das Gesamte Forstwesen. 76: 39–70. Retrieved 2 September 2025.
  10. ^ Blume, Hans-Peter; Brümmer, Gerhard W.; Fleige, Heiner; Horn, Rainer; Kandeler, Ellen; Kögel-Knabner, Ingrid; Kretzschmar, Ruben; Stahr, Karl; Wilke, Berndt-Michael (2016). "7.2.2.3 The Classification of Humus Forms". Scheffer/Schachtschabel Soil Science. Berlin, Heidelberg: Springer. p. 300. ISBN 978-3-642-30941-0.
  11. ^ Zanella, Augusto; Ascher-Jenull, Judith (2018). Humusica 1: terrestrial natural humipedons. Applied Soil Ecology. Vol. 122. pp. 1–138.
  12. ^ Zanella, Augusto; Ascher-Jenull, Judith (2018). Humusica 2: Histic, Para, Techno, Agro humipedons. Applied Soil Ecology. Vol. 122. pp. 139–296.
  13. ^ Zanella, Augusto; Ascher-Jenull, Judith (2018). Humusica 3: reviews, applications, tools. Applied Soil Ecology. Vol. 123. pp. 297–808.
  14. ^ Zanella, Augusto; Ponge, Jean-François; Gobat, Jean-Michel; Juilleret, Jérôme; Blouin, Manuel; Aubert, Michaël; Chertov, Oleg; Rubio, José Luis (January 2018). "Humusica 1, article 1: Essential bases – Vocabulary". Applied Soil Ecology. 122 (Part 1): 10–21. Bibcode:2018AppSE.122...10Z. doi:10.1016/j.apsoil.2017.07.004. Retrieved 9 September 2025.
  15. ^ Zampedri, Roberto; Bernier, Nicolas; Zanella, Augusto; Giannini, Raffaello; Menta, Cristina; Visentin, Francesca; Mairota, Paola; Mei, Giacomo; Zandgiacomo, Gabriele; Carollo, Silvio; Brandolese, Alessio; Ponge, Jean-François (27 June 2022). "Soil, humipedon, forest life and management". International Journal of Plant Biology. 14 (3): 571–92. doi:10.3390/ijpb14030045.
  16. ^ Bernier, Nicolas; Ponge, Jean-François (February 1994). "Humus form dynamics during the sylvogenetic cycle in a mountain spruce forest". Soil Biology and Biochemistry. 26 (2): 183–220. Bibcode:1994SBiBi..26..183B. doi:10.1016/0038-0717(94)90161-9. Retrieved 9 September 2025.
  17. ^ Dimbleby, Geoffrey W. (October 1952). "Soil regeneration on the North-East Yorkshire moors". Journal of Ecology. 40 (2): 331–41. Bibcode:1952JEcol..40..331D. doi:10.2307/2256803. JSTOR 2256803. Retrieved 9 September 2025.
  18. ^ Guillet, Bernard; Rouiller, James; Souchier, Bernard (October 1975). "Podzolization and clay migration in spodosols of eastern France". Geoderma. 14 (3): 223–45. Bibcode:1975Geode..14..223G. doi:10.1016/0016-7061(75)90003-8. Retrieved 9 September 2025.
  19. ^ a b Kubiëna, Walter L. (1953). The soils of Europe: illustrated diagnosis and systematics. London, United Kingdom: Thomas Murby and Company. Retrieved 15 September 2025.
  20. ^ Soil Survey Staff (1999). Soil Taxonomy: a basic system of soil classification for making and interpreting soil surveys (2nd ed.). Washington, District of Columbia: United States Department of Agriculture, Natural Resources Conservation Service. Retrieved 10 September 2025.
  21. ^ IUSS Working Group WRB (2022). World Reference Base for Soil Resources: international soil classification system for naming soils and creating legends for soil maps (PDF) (4th ed.). Vienna, Austria: International Union of Soil Sciences (IUSS). Retrieved 10 September 2025.
  22. ^ Zanella, Augusto; Bolzonella, Cristian; Lowenfels, Jeff; Ponge, Jean-François; Bouché, Marcel; Saha, Debasish; Kukal, Surinder Singh; Fritz, Ines; Savory, Allan; Blouin, Manuel; Sartori, Luigi; Tatti, Dylan; Kellermann, Liv Anna; Trachsel, Peter; Burgos, Stéphane; Minasny, Budiman; Fukuoka, Masanobu (January 2018). "Humusica 2, article 19: Techno humus systems and global change – Conservation agriculture and 4/1000 proposal". Applied Soil Ecology. 122 (Part 2): 271–96. Bibcode:2018AppSE.122..271Z. doi:10.1016/j.apsoil.2017.10.036. Retrieved 10 September 2025.
  23. ^ a b c Ponge, Jean-François (November 1999). "Horizons and humus forms in beech Forests of the Belgian Ardennes". Soil Science Society of America Journal. 63 (6): 1888–901. Bibcode:1999SSASJ..63.1888P. doi:10.2136/sssaj1999.6361888x.
  24. ^ Babel, Ulrich (1975). "Micromorphology of soil organic matter". In Gieseking, John E. (ed.). Soil components. Vol. 1. Berlin, Germany: Springer Nature. pp. 369–473. doi:10.1007/978-3-642-65915-7_7. ISBN 978-3-642-65915-7. Retrieved 11 September 2025.
  25. ^ Zanella, Augusto; Jabiol, Bernard; Ponge, Jean-François; Sartori, Giacomo; De Waal, Rein; Van Delft, Bas; Graefe, Ulfert; Cools, Nathalie; Katzensteiner, Klaus; Hager, Herbert; Englisch, Michael (15 September 2011). "A European morpho-functional classification of humus forms". Geoderma. 164 (3–4): 138–45. Bibcode:2011Geode.164..138Z. doi:10.1016/j.geoderma.2011.05.016. hdl:11577/120632. Retrieved 11 September 2025.
  26. ^ Muys, Bart; De Wandeler, Hans (29 January 2013). "Humus form description and sampling field protocol". Retrieved 11 September 2025.
  27. ^ Field Guide Humus Forms: Description and Classification of Humus Forms for Ecological Applications. Alterra. 2006.
  28. ^ Ponge, Jean-François (24 May 2005). "Fungal communities: relation to resource succession". In Dighton, John; White, James F. (eds.). The fungal community: its organization and role in the ecosystem. Boca Raton, Florida: CRC Press. pp. 169–80. doi:10.1201/9781420027891. ISBN 978-0429116407. Retrieved 11 September 2025.
  29. ^ Hagiwara, Yusuke; Matsuoka, Shunsuke; Hobara, Satoru; Mori, Akira S.; Hirose, Dai; Osono, Takashi (16 June 2015). "Bleaching of leaf litter and associated microfungi in subboreal and subalpine forests". Canadian Journal of Microbiology. 61 (10): 735–43. doi:10.1139/cjm-2015-0111. PMID 26186502. Retrieved 11 September 2025.
  30. ^ Virzo de Santo, Amalia; Rutigliano, Flora Angela; Berg, Björn; Fioretto, Antonietta; Puppi, Gigliola; Alfani, Anna (August 2002). "Fungal mycelium and decomposition of needle litter in three contrasting coniferous forests". Acta Oecologica. 23 (4): 247–59. Bibcode:2002AcO....23..247V. doi:10.1016/S1146-609X(02)01155-4. Retrieved 12 September 2025.
  31. ^ Kõlli, Raimo (February 2018). "Dynamics of annual falling debris decomposition and forest floor accumulation". Applied Soil Ecology. 123: 447–50. Bibcode:2018AppSE.123..447K. doi:10.1016/j.apsoil.2017.06.039. Retrieved 12 September 2025.
  32. ^ Joly, François-Xavier; Coulis, Mathieu; Gérard, Aurélien; Fromin, Nathalie; Hättenschwiler, Stephan (July 2015). "Litter-type specific microbial responses to the transformation of leaf litter into millipede feces". Soil Biology and Biochemistry. 86: 17–23. Bibcode:2015SBiBi..86...17J. doi:10.1016/j.soilbio.2015.03.014. Retrieved 12 September 2025.
  33. ^ Hågvar, Sigmund (July 1998). "Mites (Acari) developing inside decomposing spruce needles: Biology and effect on decomposition rate". Pedobiologia. 42 (4): 358–77. Bibcode:1998Pedob..42..358H. doi:10.1016/S0031-4056(24)00404-9. Retrieved 12 September 2025.
  34. ^ Ponge, Jean-François (November 1990). "Ecological study of a forest humus by observing a small volume. I. Penetration of pine litter by mycorrhizal fungi". European Journal of Forest Pathology. 20 (5): 290–303. Bibcode:1990FoPat..20..290P. doi:10.1111/j.1439-0329.1990.tb01141.x. Retrieved 12 September 2025.
  35. ^ Springett, Josephine A.; Brittain, John Edward; Springett, Brian Peter (1970). "Vertical movement of Enchytraeidae (Oligochaeta) in moorland soils". Oikos. 21 (1): 16–21. Bibcode:1970Oikos..21...16S. doi:10.2307/3543833. JSTOR 3543833. Retrieved 15 September 2025.
  36. ^ Galvan, Paola; Ponge, Jean-François; Chersich, Silvia; Zanella, Augusto (March 2008). "Humus components and soil biogenic structures in Norway spruce ecosystems". Soil Science Society of America Journal. 72 (2): 548–57. Bibcode:2008SSASJ..72..548G. doi:10.2136/sssaj2006.0317. hdl:11577/2270530. Retrieved 15 September 2025.
  37. ^ Frak, Elzbieta; Ponge, Jean-François (February 2002). "The influence of altitude on the distribution of subterranean organs and humus components in Vaccinium myrtillus carpets". Journal of Vegetation Science. 13 (1): 17–26. Bibcode:2002JVegS..13...17F. doi:10.1111/j.1654-1103.2002.tb02019.x. Retrieved 15 September 2025.
  38. ^ Kerley, Simon J.; Read, David J. (June 1998). "The biology of mycorrhiza in the Ericaceae. XX. Plant and mycorrhizal necromass as nitrogenous substrates for the ericoid mycorrhizal fungus Hymenoscyphus ericae and its host". New Phytologist. 139 (2): 353–60. Bibcode:1998NewPh.139..353K. doi:10.1046/j.1469-8137.1998.00189.x.
  39. ^ Lee, Kenneth Ernest; Foster, Ralph C. (1991). "Soil fauna and soil structure". Australian Journal of Soil Research. 29 (6): 745–75. Bibcode:1991SoilR..29..745L. doi:10.1071/SR9910745. Retrieved 15 September 2025.
  40. ^ Ahmad, N. (1983). "Vertisols". In Wilding, Larry Paul; Smeck, Neil E.; Hall, G. F. (eds.). Pedogenesis and soil taxonomy. II. The soil orders. Developments in soil science. Vol. 11. Amsterdam, The Netherlands: Elsevier. pp. 91–123. doi:10.1016/S0166-2481(08)70614-7. ISBN 978-0-444-42137-1. ISSN 0166-2481. Retrieved 15 September 2025.
  41. ^ Zanella, Augusto; Ponge, Jean-François; Briones, Maria J. I. (January 2018). "Humusica 1, article 8: Terrestrial humus systems and forms – Biological activity and soil aggregates, space-time dynamics". Applied Soil Ecology. 122 (Part 1): 103–37. Bibcode:2018AppSE.122..103Z. doi:10.1016/j.apsoil.2017.07.020. Retrieved 16 September 2025.
  42. ^ Tang, Jia; Mo, Yanhua; Zhang, Jiaying; Zhang, Renduo (March 2011). "Influence of biological aggregating agents associated with microbial population on soil aggregate stability". Applied Soil Ecology. 47 (3): 153–9. Bibcode:2011AppSE..47..153T. doi:10.1016/j.apsoil.2011.01.001. Retrieved 16 September 2025.
  43. ^ Morel, Jean-Louis; Habib, Leila; Plantureux, Sylvain; Guckert, Armand (September 1991). "Influence of maize root mucilage on soil aggregate stability". Plant and Soil. 136 (1): 111–9. Bibcode:1991PlSoi.136..111M. doi:10.1007/BF02465226. Retrieved 16 September 2025.
  44. ^ Rantoa, Nthatuoa Ruth; Van Huyssteen, Cornie W.; Du Preez, Chante C. (March 2015). "Organic carbon content in the soil master horizons of South Africa". Vadose Zone Journal. 14 (3): 1–12. Bibcode:2015VZJ....14..143R. doi:10.2136/vzj2014.10.0143. Retrieved 16 September 2025.
  45. ^ Andreetta, Anna; Macci, Cristina; Ceccherini, Maria Teresa; Cecchini, Guia; Masciandaro, Graziana; Pietramellara, Giacomo; Carnicelli, Stefano (30 September 2011). "Microbial dynamics in Mediterranean moder humus". Biology and Fertility of Soils. 48 (3): 259–70. doi:10.1007/s00374-011-0622-9. hdl:2158/591297. Retrieved 16 September 2025.
  46. ^ Piirainen, Sirpa; Finér, Leena; Mannerkoski, Hannu; Starr, Michael (15 May 2007). "Carbon, nitrogen and phosphorus leaching after site preparation at a boreal forest clear-cut area". Forest Ecology and Management. 243 (1): 10–8. Bibcode:2007ForEM.243...10P. doi:10.1016/j.foreco.2007.01.053. Retrieved 16 September 2025.
  47. ^ Van Breemen, Nico; Finlay, Roger; Lundström, Ulla; Jongmans, Antoine G.; Giesler, Reiner; Olsson, Mats (April 2000). "Mycorrhizal weathering: a true case of mineral plant nutrition?". Biogeochemistry. 49 (1): 53–67. Bibcode:2000Biogc..49...53V. doi:10.1023/A:1006256231670. Retrieved 16 September 2025.
  48. ^ Lång, Lars-Ove (1 May 2000). "Heavy mineral weathering under acidic soil conditions". Applied Geochemistry. 15 (4): 415–23. Bibcode:2000ApGC...15..415L. doi:10.1016/S0883-2927(99)00064-5. Retrieved 16 September 2025.
  49. ^ Kelly, Eugene F.; Chadwick, Oliver A.; Hilinski, Thomas E. (August 1998). "The effect of plants on mineral weathering". Biogeochemistry. 42 (1): 21–53. Bibcode:1998Biogc..42...21K. doi:10.1023/A:1005919306687. Retrieved 16 September 2025.
  50. ^ Zanella, Augusto; Ponge, Jean-François; Jabiol, Bernard; Van Delft, Bas; De Waal, Rein; Katzensteiner, Klaus; Kolb, Eckart; Bernier, Nicolas; Mei, Giacomo; Blouin, Manuel; Juilleret, Jérôme; Pousse, Noémie; Stanchi, Silvia; Cesario, Fernando; Le Bayon, Renée-Claire; Tatti, Dylan; Chersich, Silvia; Carollo, Luca; Englisch, Michael; Schrötter, Anna; Schaufler, Judith; Bonifacio, Eleonora; Fritz, Ines; Sofo, Adriano; Bazot, Stéphane; Lata, Jean-Christophe; Iffly, Jean-François; Wetzel, Carlos E.; Hissler, Christophe; Fabiani, Ginevra; Aubert, Michaël; Vacca, Andrea; Serra, Gianluca; Menta, Cristina; Visentin, Francesca; Cools, Nathalie; Bolzonella, Cristian; Frizzera, Lorenzo; Zampedri, Roberto; Tomasi, Mauro; Galvan, Paola; Charzyński, Przemyslaw; Zakharchenko, Elina; Waez-Mousavi, Seyed Mohammad; Brun, Jean-Jacques; Menardi, Roberto; Fontanella, Fausto; Zaminato, Nicola; Carollo, Silvio; Brandolese, Alessio; Bertelle, Michele; Zanella, Gaétan; Bronner, Thomas; Graefe, Ulfert; Hager, Herbert (5 July 2022). "A standardized morpho-functional classification of the Planet's humipedons". Soil Systems. 6 (3) 59. Bibcode:2022SoiSy...6...59Z. doi:10.3390/soilsystems6030059.
  51. ^ Thorp, James (March 1949). "Effects of certain animals that live in soils". The Scientific Monthly. 68 (3): 180–91. Bibcode:1949SciMo..68..180T. Retrieved 17 September 2025.
  52. ^ Ponge, Jean-François (February 2013). "Plant-soil feedbacks mediated by humus forms: a review". Soil Biology and Biochemistry. 57: 1048–60. Bibcode:2013SBiBi..57.1048P. doi:10.1016/j.soilbio.2012.07.019. Retrieved 17 September 2025.
  53. ^ Zanella, Augusto; et al. (January 2018). "Humusica 1, article 5: Terrestrial humus systems and forms – Keys of classification of humus systems and forms". Applied Soil Ecology. 122 (Part 1): 75–86. doi:10.1016/j.apsoil.2017.06.012. hdl:11577/3252690.
  54. ^ a b c Klinka, K.; Green, R.N.; Trowbridge, R.l; Lowe, L.E. (1981). "Taxonomic classification of humus forms in ecosystems of British Columbia. First approximation" (PDF). Land Management Report Ministry of Forests British Columbia (Canada). 8. ISBN 0-7719-8659-9.
  55. ^ "Humus". Encyclopedia Britannica.
  56. ^ "Humus". National Geographic.
  57. ^ "Soil Organic Matter and Humus Classification". gaia.flemingc.on.ca. Retrieved 2022-04-21.
  58. ^ Klinka, K.; Green, R.N.; Trowbridge, R.l; Lowe, L.E. (1981). "Taxonomic classification of humus forms in ecosystems of British Columbia. First approximation" (PDF). Land Management Report Ministry of Forests British Columbia (Canada). 8. ISBN 0-7719-8659-9.
  59. ^ Bernier, B (1968). "Descriptive outline of forest humus form classification". Proceedings 7th Meeting of the National Soil Survey Committee of Canada. 39: 154.
  60. ^ Wiesmeier, Martin; Hübner, Rico; Kögel-Knabner, Ingrid (2015). "Stagnating crop yields: An overlooked risk for the carbon balance of agricultural soils?". Science of the Total Environment. 536: 1045–1051. Bibcode:2015ScTEn.536.1045W. doi:10.1016/j.scitotenv.2015.07.064. PMID 26235605. Early signs of a reduction in humus stocks due to the stagnating harvest yields can already be observed. Initial indications of humus depletion in arable soil have been observed in almost all EU countries in recent years.
  61. ^ Garcia-Franco, Noelia; Wiesmeier, Martin; Buness, Vincent; Berauer, Bernd J.; Schuchardt, Max A.; Jentsch, Anke; Schlingmann, Marcus; Andrade-Linares, Diana; Wolf, Benjamin; Kiese, Ralf; Dannenmann, Michael; Kögel-Knabner, Ingrid (2024). "Rapid loss of organic carbon and soil structure in mountainous grassland topsoils induced by simulated climate change". Geoderma. 442 116807. Bibcode:2024Geode.44216807G. doi:10.1016/j.geoderma.2024.116807. The [reduced] size of the soil clods could be an early warning signal for the impending loss of humus and soil structure
  62. ^ Zanella, Augusto; Ponge, Jean-François; Hager, Herbert; Pignatti, Sandro; Galbraith, John; Chertov, Oleg; Andreetta, Anna; Nobili, Maria (2018). "Humusica 2, article 18: Techno humus systems and global change – Greenhouse effect, soil and agriculture". Applied Soil Ecology. 122: 254–270. Bibcode:2018AppSE.122..254Z. doi:10.1016/j.apsoil.2017.10.024. (WPeditor Note)The article is structured in six sections. A first portion is dedicated to the state of the art concerning climate change and agriculture. Internet-available IPCC maps and cartographic documents created by scientific research centers were used to illustrate forecasted climatic changes. In Sections 2 and 3, bibliographic evidence was collected to support a vegetation-soil co-evolution theory. Humus, soil, and vegetation systems are presented at the planet level in many synthetic maps. Sections 4, 5, and 6 cover human influence on soil evolution during the Anthropocene. Humans have detected and utilized Mull humus landscapes across the planet for crop production and pasture. Human pressure impoverished these humus systems, which tend to evolve toward Amphi or Moder systems, losing their natural biostructure and carbon content.