Draft:Clay-humus complexes
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In soil science, clay-humus complex (CHC) refers to the aggregate formation of organic fragments such as humic substances with inorganic particles such as clay minerals through hydrogen bonds or the incorporation of metallic cations.[1] Both clay minerals and humic substances are soil colloids.[2]
Formation
[edit]Humic substances are able to bind individual soil particles together to form a crumb structure and thus stabilise the soil structure. Such aggregate structures are formed from clay colloids by the combination of calcium bridges with humic substances in humic topsoils. While the clay minerals and the humic acid residues (organic dipoles) of the humus particles are negatively charged, the Ca2+ ion or other polyvalent cations, for example Mg2+, form a neutralising bridge. The resulting organo-mineral compounds are known as clay-humus complexes (CHC) or lime-clay-humus complexes.
A particularly intensive mixing of organic and mineral substances takes place in the earthworm’s gut, where the aggregates are stabilised by mucilage. Bacteria and fungi further break down the resulting CHC into soil crumbs. This living building up only takes place when soil life is very active in humus- and nutrient-rich topsoils, in which an optimal crumb structure and the humus form ‘mull’ can form.[3][4]
Significance
[edit]The complex formed stabilises the soil against erosion and siltation, creates favourable conditions for the air and water balance in the pore volume of the soil and thus increases soil fertility. By binding the positively charged nutrient salt ions, these important substances for the plant cannot be washed out by rain into deeper soil layers. They are later released and utilised by the plant through ion exchange from the CHCs.
The elasticity of the formed crumb structure is favourable for the stability of the soil and the long-term supply of plants with water and nutrients, as it ensures better air and water permeability of the soil. Tilth (soil fermentation) is promoted more sustainably by soil life with the formation of clay-humus complexes than is possible with frost fermentation, for example. The physically induced structures of the segregate are only favourable for plant cultivation for a short time because they quickly lose their function due to cracking and further decay.
Excessive tillage, however, leads to the disintegration of any crumb structure—in horticulture, this cultivation error is referred to as ‘dead tilling’ of a soil.
References
[edit]- ^ Gisi, Ulrich, ed. (1997). Bodenökologie: 51 Tabellen. Bücher Biowissenschaften (2., neu bearb. und erw. Aufl ed.). Stuttgart: Thieme. ISBN 978-3-13-747202-5.
- ^ Kuntze, Herbert; Roeschmann, Günter; Schwerdtfeger, Georg (1994). Bodenkunde: 188 Tabellen. UTB für Wissenschaft Große Reihe Botanik, Ökologie, Agrar- und Forstwissenschaften (5., neubearbeitete und erweiterte Auflage ed.). Stuttgart: Verlag Eugen Ulmer. ISBN 978-3-8001-2651-4.
- ^ Scheffer, Fritz; Schachtschabel, Paul (1992). Lehrbuch der Bodenkunde: 102 Tabellen (13., durchges. Aufl ed.). Stuttgart: Enke. ISBN 978-3-432-84773-3.
- ^ Heistinger, Andrea; Grand, Alfred (2017). Biodünger selber machen: Regenwurmhumus, Gründüngung, Kompost (4. Auflage ed.). Innsbruck: Löwenzahn. ISBN 978-3-7066-2519-7.