World’s Soil Resources

6.5.2 | Causes of soil salinity
The distribution of salt-affected soils varies geographically with climate, landscape type, agricultural
activities, irrigation methods and policies related to land management.
Natural causes of salinity and sources of salt
1. Rock weathering: Significant quantities of sodium, and to a lesser extent chloride, occur widely in the
parent rocks from which soils form. Over time, rock weathering can lead to appreciable salt accumulation
in soils if leaching is restricted. Rock weathering is the primary source of salt in seawater.
2. Sea water and accession of salt in marine sediments: Saline soils can form from sediments and parent materials
that were once under the sea. Likewise, the salts can be due to tidal inundation. Typical examples include
the pseudo-delta of Senegal and the Gambia and in the Philippines where coastal tideland reclamation
has created about 0.4 million ha of agricultural salt-affected soils. In the United Arab Emirates, areas
along the coastal sabkha (salt marshes or lagoonal deposits) are highly salinized (28.8 dS m -1 ). In the
coastal region of the Abu Dhabi Emirate, salinity is more than 200 dS m -1 (Abdelfattah and Shahid, 2007)
3. Atmospheric deposition: Salt derived from the sea, either deposited via rain or dry fallout, is the primary
source of salt across large areas: for example, many millions of hectares in southern Australia. In arid
areas, salt can also be derived from dry lake beds and then blown considerable distances by wind (e.g.
Eurasia and parts of Australia).
Human-induced causes
1. The management of land and water resources is responsible for the development of human-induced
saline and sodic soils. The main causes are:
2. Poor drainage facilities which induce a rise of the groundwater table. This is a major cause of soil
salinization in India, Pakistan, China, Kenya and the Central Asian countries.
3. The use of brackish groundwater for irrigation. This is a major cause of secondary salinization in parts
of Asia, Europe and Africa.
4. The intrusion of seawater in coastal areas, for example in Bangladesh.
5. Poor on-farm water management and cultural practices in irrigated agriculture.
6. Continuous irrigation over very long periods, particularly in the Middle East.
7. Replacement of deep rooted perennial vegetation with shallower rooted annual crops and pastures
that use less water leading to the rise of saline groundwater, for example southern Australia.
6.5.4 | Trends and impacts
Soil salinity is becoming a significant problem worldwide. From the very scattered information on the
extent and characteristics of salt-affected soils, salinity and sodicity are rapidly increasing in many regions,
both in irrigated and non-irrigated areas. Increasing soil salinity problems are taking an estimated 0.3 to 1.5
million ha of farmland out of production each year and decreasing the production potential of another 20 to
46 million ha. The annual cost of salt-induced land degradation was estimated in 1990 at US$ 264 ha−1. By
2013, the inflation-adjusted cost of salt-induced land degradation was reported as US$ 441 ha–1 (Qadir et al.,
2014).
6.5.5 | Responses
There are many available responses to contain the salinity threat. These include: (1) direct leaching of salts;
(2) planting salt tolerant varieties; (3) domestication of native wild halophytes for use in agro-pastoral systems;
(4) phytoremediation (bioremediation); (5) chemical amelioration; and (6) the use of organic amendments.
Status of the World’s Soil Resources | Main Report Global soil status, processes and trends
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