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Pakistan – Qureshi and Barrett-Lennard 1998 ) or in situations where perennial veg-
etation is substituted by annual vegetation, which also causes groundwater rise (e.g.
Australia – Peck 1978 ; Peck and Hatton 2003 ).
Soils can be considered salt affected if the presence of water-soluble salts affects
normal plant growth (especially agricultural production), environmental values or
economic welfare (Rengasamy 2006 ; FAO 2015 ). While the total affected area at
any one site may be relatively small, the patchy nature of salt expressions at the land
surface often disturbs the ability to farm surrounding areas making it a large overall
problem. Increased salt load to rivers can also lead to downstream impacts.
Drivers for secondary salinity are a result of human-induced changes to the
hydrological balance of a landscape, including large increases in recharge (e.g. irri-
gation water), or through removal of deep-rooted vegetation that used to intercept
and/or transpire a higher proportion of incoming rain than the dryland agriculture
system (dryland salinity).
A change in land use allows opportunity for increased recharge to underlying
aquifers or can increase the sodicity of the soil as salts build up in the near-surface
soil profile to the detriment of plants and microorganisms that form beneficial sym-
biotic associations with the plants. This imbalance can be caused by shallow-rooted
annual crops and pastures replacing deep-rooted trees or perennial native grasses.
Not all dryland salinity is caused by groundwater. The salinity of the soil solution
needs to be excessive for the plants that needs to grow, usually agricultural but
native plant species can also be impacted by dryland salinity (George et al. 1995 ).
The salinity of soil solutions increases as plants take up fresh water and this can
result in it becoming too saline for plants, especially as soils dry out seasonally
(termed ‘transient salinity’ by Rengasamy ( 2006 )).
This chapter provides an overview of dryland salinity – its causes, forms and
management options. It also examines how climate change may affect both its
future extent and the viability of management and recovery options. Examples are
drawn mainly from Australia, a continent with major dryland salinity problems,
which has resulted in a body of research that may be useful for other parts of the
world experiencing dryland salinity. However, there are types of dryland salinity
that do not occur in Australia and so we have used other examples where
available.
2 Worldwide Extent of Dryland Salinity
Saline soils have been identified in over 100 countries, in most continents and have
been estimated to affect over 954.8 M hectares of land (Szabolcs 1989 ). The FAO
( 2015 ) have estimated the global extent of saline and sodic soils to be as shown in
Table 1. About 19.5 % of irrigated land (45 M ha) was considered salt-affected but
only 2.1 % of dryland agricultural soils was salt affected (32 M ha). By this estimate,
Asia, the Pacific and Australia have almost half of the world’s salt-affected soils and
about two-thirds of the world’s sodic soils. Up to a third of Australian soils are sodic,
D.J. McFarlane et al.