The publication of this Handbook was supported by the Russian Federation

Main types and sources of  salts
There are 2 main types of  soil salinity:
•  primary salinity due to natural causes
•  secondary salinity due to irrational land use and inappropriate agricultural practices
Primary salinity occurs naturally in soils and waters. Natural salt accumulation processes are 
associated with certain types of  relief, geomorphological and hydrogeological conditions. The 
latter imply a high groundwater table, impeded drainage or even an absence of  drainage with only 
evaporation and transpiration processes to control the groundwater table. In arid climates, relic salt 
accumulations tend to be preserved and modern salt accumulation processes are in progress occur 
within the accumulative types of  landscapes under hydromorphic condition.
Secondary salinity occurs as a consequence of  excessive water 
inputs via irrigation and leaching of  soils in the absence of  
appropriate drainage systems, which causes a rapid raising of  
the groundwater table. At the present time, the development 
of  secondary salinization represents an important problem in 
sustaining the health of  arid ecosystems (FAO SPUSH, 2001) 
[21] .
The main sources of  soil salinity are salts originally present 
within parent materials, mineralized ground and surface waters as well as wind-blown deposits.
An assessment of  the causes of  salinity within a specific area requires consideration of  the following 
factors:
•  The presence of  salt-containing deposits or saline parent materials. Modern soil salinity is 
often caused by the influence of  strongly saline sediments and, especially, deposits of  rock salt 
and salt domes.
•  Aeolian transport of  salts from the sea surface (salt spray) and also from the surface of  
Solonchaks. This process is extensively developed in both coastal areas and inland, e.g., 
Western Siberia and the areas of  the Aral Sea and Lake Balkhash.
•  Hydrogenic salt accumulation is an important source of  salts in soils within the areas of  
groundwater springs and shallow groundwater tables.

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9
Chapter 1.Salt-affected soils of the Eurasian Region: diagnostics, criteria and distribution 
•  Biogenic salt accumulation associated with the ability of  plants to accumulate certain salts 
and later return these to soils as plant litter undergoes decomposition.
•  Use of  highly mineralized irrigation water can cause strong soil salinization within irrigated 
fields.
Research into genesis and sources of  salinity should involve another important consideration. 
Salts  that  enter  a  soil  can  undergo  significant  changes.  They  can  be  present  in  soil  solution, 
undergo precipitation or exchange reactions, which implies the development of  processes of  salt 
transformation, vertical re-distribution and interaction with the solid and liquid phases of  soils, i.e., 
salts take part in soil formation.