Geoscience Reference
In-Depth Information
Upland
sites
Climate increasingly
cool and wet
Lowland
sites
1 Permafrost soil processes (cryopedology)
2Leaching.
3 Clay translocation.
4 Podzolization.
5 Decalcification.
6 Calcification.
7 Gleying.
8Rubefaction.
9 Salinization.
10 Alkalization.
11 Solodization.
12 Laterization.
atmospheric pollution by sulphur dioxide (SO
2
) and
nitrogen oxides produces an even more acid leachate,
'acid rain'. Also, as it passes through the surface organic
horizon, it dissolves organic acids from decomposing
plant residues. It is thus able to dissolve and decompose
minerals and carry away cations and anions dissolved in
the soil solution. The basic cations (bases) held on the soil
colloids (calcium, magnesium, potassium, sodium) are
released from the colloid surface and replaced by hydrogen
or aluminium ions. This leads to a lower pH and
percentage base saturation as leaching progresses. Thus
soil pH is a good general indicator of the intensity of
leaching, which is related to the amount of annual rainfall
and the chemistry and texture of the soil parent material.
The leaching of bases is an important process
ecologically and agriculturally, as the ions are moved
downwards out of the rooting zone of plants. In natural
vegetation it is important that deeply rooting species (e.g.
grasses, deciduous trees in the temperate zone) are able
to recycle nutrients from deep in the subsoil and thus act
Soil-forming processes of leaching,
decalcification and calcification
The process of leaching is caused by the continual washing
of the soil with rainwater. Rainwater has a natural pH of
about 5ยท5, owing to dissolved carbon dioxide, making it
a weak hydrocarbonic acid (H
2
CO
3
). In some regions
