PODZOLISATION

PODZOLISATION (CHELUVIATION) It is a process widespread in acidic soils. In these cases, because of the different solubility of the various minerals, a situation develops in which the upper layers of the soil become rich in silica, tending towards pure quartz, and take on a cha:-1.cteristic ash-grey appearance. The lower alluvial ho­rizon is rich in sesquioxides of iron. The basic cause of these'
translocations lies in the leaching action of certain organic compounds known as chelating agents. Podzol profiles are usually associated with coniferous and heathland vegeta­tion. Podzol soils extend in a broad belt across Russia and North America.

GLEYING The process occurs in wet or waterlogged soils. The anaerobic (oxygen-deficient) conditions lead to the process of red.uction in which ferric oxide is reduced to ferrous oxide. This gives the soil a blue-grey colour. This horizon is called gley, a compact layer of sticky structureless day. The gley horizon usually occurs within the zone of permanent groundwater situation. Where the soil periodi­cally dries out, the ferrous solutes may oxidise back into the ferric state. Since this process is not uniform, it gives the soil a mottled or blotchy look, typified by patchy red colours.