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Berlin Environmental Atlas

01.06 Soil-Scientific Characteristic Values (Edition 2002)

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01.06.4 Utilizable Capillary Capacity of the Effective Root Zone


Description

An assessment of the hydrologic budget via the utilizable capillary capacity in the effective root zone (nFKWe) yields a differentiated analysis of the water available to plants at any location. The different rooting depths and root zones are taken into account, in accordance with soil type and use. Thus, forests and groves have a considerably greater root zone than, e.g. garden uses. In sandy soils, the effective root zone is lower than in loamy soils. In loamy soils, precipitation water is retained longer than in sandy soils, so that it is advantageous for plant roots, in terms of the water and nutrient balance, to develop a larger root zone than in sandy substrata. In boggy soils, the effective root zone only extends down to the zones affected by groundwater, so that only the top 20-30 cm usually serve as a root zone. The reason for the shallow root zone is the lack of air in the permanently water-saturated zones. Therefore, with the exception of some specialist plants, roots are confined to the upper zones, which conduct both sufficient air and water.

The additional water supply to the plants from the capillary rise of the groundwater during the vegetation period, which decisively influences the nFKWe at low land-parcel intervals, was not taken into account in the present investigation.

Methodology

The ascertainment of the nFKWe for soil associations in dependence on actual land use was carried out by the soil science branch of the TU Berlin in the context of an expert report (Plath-Dreetz/ Wessolek/ Renger 1989).

First, the effective root zones for Berlin locations appropriate to the respective uses were taken from Table 1 Based on the depth of the effective root zones, the usable capillary capacities ascertained for each zone for the sample profiles documented by Grenzius (1987) were added up to form the nFKWe. Appropriate correction factors for organic substances were taken into account. Since different soil types appear within a soil association, a range is derived which can be described by the minimum and maximum value of the nFKWe per soil association. In addition, the typical nFKWe value for the respective soil association, which is represented in the map, is determined depending on use.

Table 1: Depths of the Effective Root Zone (in dm), by Soil Type and Use
  Farmland
Gardens
Cemeteries
Grassland Forest Parks Allotment Gardens
Sands 6 5-6 10 7 6
Loams 7 6-7 12 8 7
Boggy soils (groundwater influenced) - 2-3 4 4 4
Table 1: Depths of the Effective Root Zone (in dm), by Soil Type and Use
(Plath-Dreetz et al. 1988)

The results were compiled in five stages (Tab. 2):

Table 2: Gradation of the Utilizable Capillary Capacity of the Effective Root Zone
nFKWe [mm] Stage Designation
<60 1 very low
60 - <140 2 low
140 - <220 3 medium
220 - <300 4 high
≥300 5 very high
Table 2: Gradation of the Utilizable Capillary Capacity of the Effective Root Zone
(Soil-Scientific Mapping Directive 1994)

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