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Berlin Environmental Atlas

01.06 Soil-Scientific Characteristic Values (Edition 2013)

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01.06.8 Sum of Exchangeable Alkaline Cations in the Topsoil (S-Value)


Description

The exchangable cations in the soil are usually distinguished as acidic and alkaline cations, respectively. The former include primarily hydrogen ions (H-ions), and also those, especally Al ions, which trigger hydrolysis when released into the soil solution, and thus release H-ions; their sum is known as the H-value. The alkaline cations are primarily Ca2+, K+ Mg2+ and Na+, and, in agricultural soil (after fertilizing), also NH4+, with Ca2+ usually dominant, with more than 80 %. Their sum is known as the S-value. Its concentration can be given in cmolc/kg, and its quantity in molc/m². The percentage share of the S-Value in exchangable cations is known as alkaline saturation.

The S-value thus describes the quantity of the cations provided by the soil which is relevant for plant nutrition, and is hence an important indicator of soil fertility

Methodology

The quantity of exchangable alkaline ions (S-Value) for topsoil (here, 0-3 dm) can be calculated by multiplying the effective cation interchagable capacity (CECeff) by alkaline saturation, considering packing density and coarse fractioin.

The calculation of effective cation exchangable capacity is shown in map 01.06.09. The alkaline saturation can thus be calculated from the pH value (CaCl2).

Ascertainment is accomplished using the pH value typical of the location of the topsoil, (cf Map 01.06.07); the alkaline saturation is derived according to Table 1. Then, a linear interpolation between these pH stages of this table is carried out.

Table 1: Relationship between Alkaline Saturation in % and the pH (CaCl2) of Mineral Soil Zones in Berlin
pH
(CaCl2)
BS
[%]
3 2
3.1 3
3.2 4
3.3 5
3.4 6
3.5 7
3.6 9
3.7 11
3.8 13
3.9 15
 
pH
(CaCl2)
BS
[%]
4 18
4.1 20
4.2 23
4.3 25
4.4 28
4.5 31
4.6 34
4.7 38
4.8 41
4.9 44
 
pH
(CaCl2)
BS
[%]
5 47
5.1 50
5.2 53
5.3 56
5.4 60
5.5 63
5.6 66
5.7 69
5.8 72
5.9 75
 
pH
(CaCl2)
BS
[%]
6 77
6.1 80
6.2 82
6.3 85
6.4 87
6.5 89
6.6 91
6.7 93
6.8 95
6.9 96
 
pH
(CaCl2)
BS
[%]
7 97
7.1 98
7.2 98
7.3 98
7.4 99
7.5 99
7.6 99
7.7 100
7.8 100
7.9 100
Table 1: Relationship between Alkaline Saturation in % and the pH (CaCl2) of Mineral Soil Zones in Berlin (Grenzius 1987)

Table 2 shows the S-values, classified into 1-10 categories (extremely low – very high).

Table 2: Gradation of S-Value
Alkaline Saturation
[molc/m²]
Level Designation
<1 1 extremly low
1 - <2 2 very low
2 - <3,5 3 moderate to very low
3,5 - <5 4 moderate low
5 - <10 5 low
10 - <25 6 moderate
25 - <50 7 medium
50 - <100 8 moderate high
100 - <200 9 high
>200 10 very high

The categorization of low level values is carried out in very small stages, in order to show the precise gradation necessary for an evaluation of the function "habitats for near-natural and rare plant communities" in low-nutrient soil.

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