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Berlin Environmental Atlas

01.06 Soil-Scientific Characteristic Values (Edition 2013)

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01.06.5 Organic-Matter Shares


Description

The organic fraction of soils consists of the transformed remains of dead plants and animals. The humus is formed by mulch and humin materials. The high sorption capacity of the humin materials, the high share of nutrients available to plants, and favourable qualities for the hydrologic budget characterize many soil functions. The humus content of mineral soils is determined by soil genesis and use. Such uses as horticulture with introduction of compost, or intensive pasturing favour humus enrichment, while other uses show a considerably lower organic-substance content (cf. Tab. 1).

Wet vegetation locations, e.g. flood-plain soils and mires, have high biomass production but low humus reduction. The enriched organic substance is present in the form of peats of varying degrees of decomposition. Bogs and semi-bogs have organic substance contents of 15 - 80 %, depending on their use and the degree of decomposition of the peat. The prerequisite for a high organic substance content is permanent wetness in the topsoil and near-natural utilization, such as extensive pasturing.

The organic-matter shares represent the quantity of organic substance present at a location for a defined soil lot, depending on soil type and land use. The amount of humus is primarily an indicator of the nitrogen stock and the easily mobilizable nitrogen proportion. But other important nutrients such as potassium, calcium, magnesium and phosphorus are also released and made available to plants by means of the decomposition and humification of organic substances. In addition to the availability of nutrients, the organic fraction functions as a nutrient and water reservoir, and is able to bind pollutants to a high degree. The organic content of a soil depends on the humus content and the thickness of the humus zone. This differs according to soil type and use. Thus, for example, damp boggy locations with high biomass production and low decomposition have a high humus quantity, and sandy dry soils with low vegetation coverage have a low humus quantity.

Methodology

The average organic content of mineral soils depending on soil type and use was taken from investigations by Grenzius (1987) and soil analyses performed under the Heavy-Metal Investigation Programme (1986, 1987). These data were initially evaluated by Fahrenhorst et al. (1990)and the average humus content ascertained for the characteristic soil type of the various soil associations at different uses An expansion of the database using various specific mappings was carried out in 1993 (Aey 1993). A rough orientation, purely by use, is shown in Table 1.

Table 1: Average Humus Contents by Use
Use Organic Content
[% by mass]
Residential areas 5
Mixed areas 3
Core areas 3
Commercial and industrial areas 3
Special uses, utilities 3
Weekend home areas 6
Forest 4
Grassland 12
Farmland 3
Parks, green spaces, city squares 3
Cemeteries 4
Allotment Gardens 6
Fallow areas, meadow-like vegetation 3
Fallow areas, bushes, trees 4
Camping and sports facilities 4
Tree nurseries 4
Table 1: Average Organic Contents by Use, compiled from Fahrenhorst et al. (1990)

The humus contents of peats formed at wet locations are not taken into account for mineral soils; their contents and thicknesses are listed separately in the investigation of humus quantity.

Humus quantity was ascertained from humus content of the humus layer, taking into account peat quantity [mass %] and the effective retention density and thickness of the organic zones.

Humus quantity ascertained for the various locations was broken down into five stages, according to Table 2.

Table 2: Gradation of Oganic Content
Organic Content [kg/m²] Stage Designation
0 - <5 1 very low
5 - <10 2 low
10 - <20 3 medium
20 - <100 4 high
100 - <2000 5 very high
Table 2: Gradation of Oganic Content, according to Results from Berlin Soils
(Gerstenberg, 2013)

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