Humic substance
Humic substances are high molecular substances in the humus soil that have a non-uniform ( amorphous ), macromolecular structure. They can be described as the first reasonably stable, dark-colored structural product made from the matter of a dead living being.
Although the chemical structure of the macromolecules cannot be determined for the most part, the basic structure can be recognized. The humic substances consist of nuclei, bridges and reactive side groups. Benzene , indole , pyrrole , naphthalene , pyridine , quinoline or furan are often found as nuclei . Primarily oxygen , nitrogen , carbon , simple hydrocarbons or secondary carboxylic acid amides act as bridges . The side groups are essentially carboxy , carbonyl , methoxy , amino and hydroxyl groups. With regard to their chemical structure, humic substances can only be described statistically, as they form a mixture of substances that changes from place to place and from season to season.
Classification
One differentiates:
- Humins : insoluble substances;
- Fulvic acids : are readily soluble in acidic and basic ;
- Humic acids : are soluble in the base and are used, for example, to bind heavy metals .
Share in soils
Humic substances are present in different proportions depending on the soil:
- Arable soils : 1–2%
- Black earth: 2–7%
- Meadows : approx. 10%
- Bog soils : 10–20%
Ecological properties
Food source
Due to their high molecular weight, humic substances are difficult to break down. The degradation usually takes place cometabolically (see also priming effect) and under aerobic conditions. Cometabolic means that the humic substances are not used as the sole source of carbon , but can only serve to supply nutrients (primarily nitrogen , sulfur , phosphorus ). Microorganisms that break down humic substances are, for example, actinomycetes , streptomycetes , Pseudomonas and fungi, such as mushrooms or penicillium (see penicillin ).
Effect on plants
In laboratory tests, a promotion of plant growth by humic substances could often be observed. This is attributed to the following causes:
- Humic substances have a high cation exchange capacity (good availability of cations).
- Mineralization means a delivery of nutrients (nitrogen, sulfur, phosphorus).
- Humic substances have a hormone-like effect, although it is not clear whether the humic substances themselves have a hormone- like effect or whether the hormones are adsorbed on their surfaces .
- Humic substances support the absorption of micronutrients such as iron and copper .
- Local detoxification takes place due to their ability to bind metal ions (especially aluminum ).
Effect on aquatic animals
Studies on the nematode Caenorhabditis elegans have shown that humic substances exert chemical stress, which, however, can have positive effects on the organism if it is not too strong. The animals exposed to some humic substances acquire multiple stress resistances, which can even have a life-prolonging effect.
In embryos and young fish, such as those of the swordtail , the addition of the synthetic humic substance HS 1500 improved weight gain and growth in size. In addition, the populations studied developed predominantly female juveniles, so that an estrogenic potential of the humic substances can be assumed.
Web links
proof
- ↑ Scheffer / Ulrich Textbook of Agricultural Chemistry and Soil Science, III. Part, humus and humus fertilization, first volume , 2nd edition, 1960
- ↑ Kuntze / Roeschmann / Schwerdtfeger Bodenkunde , 5th edition, 1994, ISBN 3-8252-8076-4
- ↑ Steinberg / Menzel humic substances - dead material highly active. Studies on vital brown geopolymers in aquaristic trade magazine No. 205 February / March 2009 ISSN 1437-4854
- ↑ Steinberg / Menzel humic substances - dead material highly active. Studies on vital brown geopolymers in aquaristic trade magazine No. 206 April / May 2009 ISSN 1437-4854