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Nutrient supply in the soil (E6)
 
Soils highly loaded with nitrogen cause plant diversity to decline. Species able to benefit from the overly rich nutrient supply will grow rapidly, displacing competitors that prefer nutrient-poor soils with a low nitrogen content.

The E6 indicator registers the nutrient supply in Switzerland’s soils. From a biodiversity point of view, low nutrient values are considered to be a good sign.
 
 
Development in Switzerland
 

The so-called nutrient value reflects plant preference for high or low nutrient supply in the soil. On a scale from 1 to 5, high values signify soils rich in nutrients, while low values stand for soils poor in nutrients:

1) extremely poor
2) poor
3) neither very nutrient-poor nor heavily fertilized
4) nutrient-rich
5) overfertilized.

The following table lists mean nutrient values of various Swiss soil types subject to different forms of land use (arithmetic mean including a 95% confidence interval, samples taken on sampling areas of 10 square meters each). “Mountains” include areas not used for alpine farming (such as scree plant communities, turf, and dwarf shrub heath), but exclude glaciers and inaccessible rocks.

 
Arable land
 Settlements Meadows Forests Alpine pastures Mountains
             
Mean nutrient value 3,8±0,0 3,5±0,1 3,2±0,1 2,9±0,0 2,3±0,1 2,3±0,1


Reading example
The mean nutrient value of Switzerland’s meadows lies between 3.1 and 3.3.


The map below depicts the nutrient supply distribution in Switzerland’s grassland zone (meadows, pastures or alpine pastures, sampling areas of 10 square meters each).

Comments
Nutrient supply is richest on arable land, immediately followed by settlement areas. Areas subject to less intense use, such as alpine pastures or mountain areas not cultivated at all, are characterized by lower nutrient supplies. Moreover, soils at high altitudes predominantly hold only a thin humus layer, or lack a humus layer altogether. Due to their steep inclination, erosion hampers the formation of the nutrient-rich humus layer. Soils at lower altitudes tend to be more level, favoring humus buildup and hence a higher nutrient supply.
 
 
Development in the Regions
 
Please consult the complete E6 data sheet for detailed information on comparison by altitudinal zones.
 
 
Significance for biodiversity
 
While nitrogen is vital for all plant survival, plant diversity starts to dwindle once the nitrogen content of the soil is too high. Species able to benefit from the increased nutrient supply invade the sites of weak competitors, possibly displacing them altogether. An excess supply of other important nutrients such as phosphorus and potassium has a similar effect.

Wherever the number of plant species is low, small animal and insect diversity is reduced as well. Consequently, increasing the soil’s nutrient supply is harmful from a biodiversity point of view.
 
 
Further Information
 

Responsible for E6
Béatrice Nussberger nussberger@hintermannweber.ch, +41 (0)31 312 82 72

Additional source of information
> FOEN website: air pollution, nitrogen deposition map
> Institute for Applied Plant Biology: research on the nitrogen load of forests
> Co-operative programme for monitoring and evaluation of the long-range transmissions of air pollutants in Europe
 
 
Data sheets
 
> Complete data sheet E6 (592 KB)
 
 
Status
 
The information given here is based on document 680 321.10 Produkt E6 V1_en dated 5 December 2007.

Data will be updated after the second BDM Z9 plant survey has been completed.
 
 
 
     
       
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