The salinity condition in the plant
root zone prevents water uptake from soil by plants, because of the presence of  osmotic potential in soil
water
due to existence of salts, which finally, decreases transpiration of plants lead to decline crop yield. Once the soil is
affected by salts, soluble salts lower the osmotic potential of the soil water,
making it more difficult for roots to remove water from the soil in required
amount and rate to meet their evapotranspiration demand. This process affect
the plant water uptake even if the soil has sufficient quantity of water in
root zone ( Clark, 1990; Lamsal
et al., 1999).

Salt
concertation in soil solution reduces crop growth and yield  by reducing the ability of plant roots to
acquire water lead to nutrient deficiencies or toxicities ( Ganjegunte
et al., 2008; Kravchik & Bernstein, 2013; Deinlein et
al., 2014; Reddy et
al., 2015). This is because water in principle
flow from the high water potential (low salts in plant cells) to low potential
(high salts in soils) or it flowing from less negative potential to more
negative potential which controlled by gradients in water potential.  High soil salinity causes dehydration of
plant cells results in reduced plant growth and regularly death. Dissolved
salts cause dehydration of plant cells because the osmotic potential of soil
water is decreased. Therefore, plants cannot easily extract water from soils when
soil solutions have lower osmotic potentials than plant cells (Zhang, 2014).

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To
maintain water uptake from a dry or saline soil, plants must decrease their
internal water requirement below that of the soil water content.  The degree to which plants can adjust to dry
and saline conditions depends on their ability to balance a water need below
that of the soil and their ability to tolerate high concentrations of NaCl
present in the root zone (Nemati et al., 2011; Reddy et al., 2015). 
Salinity not only affects the final soil water content which plants can
extract to, but also the rate at which they use water (Fujimaki et al., 2008).

Therefore,
it is very important to assess salinity stress on crop yield to see the extent
of yield decrease under different salinity conditions. Generally, crops are
most sensitive to salinity during root emergence and germination, some of
plants are most sensitive, some are resist, however the sensitivity of crop
depends on their growth characteristics and root system (Zhang, 2002). Tolerance
to salinity may therefore involve variations in responses to each of these
factors (Munns & Tester, 2008).