Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 280

8.3.1.1 Saline Soil

Salinity refers to the amount of salts in soils. Saline soils are high in soluble salts but
low in sodium. When a solution extracted from saturated soil is 2.0 dS/m or greater,
the soil is saline. This soil is commonly referred to as white-alkali soil due to the
formation of white crust on soil surface.

Characteristics:
•

Electrical conductivity (EC) is greater than 2 dS/m, showing higher soluble salt
concentration

• Exchangeable sodium percentage (ESP) is less than 15 (or, sodium absorption

ratio, SAR value is less than 13), indicating low level of exchangeable sodium

The principal cations are Ca ++ and Mg ++ with smaller amounts of Na +

• and

K + ions

The Cl - and SO 4 - are the dominant anions with lesser amounts of HCO 3 -

•

• The pH value of this soil is generally less than 8.5.

Saline soils are formed from the accumulation of salts. There are many differ-
ent types of salt and they vary in ability to create saline soils. Basically, the more
soluble a salt is, the more it can contribute in forming saline soil. Some common
salts are listed in Table 8.3 along with their corresponding solubility. Gypsum and
lime are present in some saline soils but their low solubility indicates they are not
as damaging as other salts such as Glaubers's and Epsom salts.

Table 8.3 Some common salts and their solubility in water

Salt Chemical formula Solubility (g/l)

Calcium carbonate (lime) CaCO 3 0.01

Calcium sulfate (gypsum) CaSO 4 2

Magnesium sulfate (epsom salt) MgSO 4 300

Sodium sulfate (Glauber's salt) Na 2 SO 4 160

Saline soils often are in normal physical condition with good structure and per-
meability. They are characterized by irregular plant growth and salty white crusts
on the soil surface. These salts are mostly sulfates and/or chlorides of calcium and
magnesium. In many cases, it is possible to see the salts in the soil when they precip-
itate out of solution. Salts are not always visible. For example, lime is quite difficult
to see in the soil. Soil can easily be tested for lime by applying a dilute acid such as
HCl to the soil; fizzing and bubbling indicates its presence. Soil salinity is a limita-
tion where plant growth is reduced due to the presence of soluble salts in soil which
holds water more tightly than the ability of plants to extract water from the soil. As a
result, many plants exhibit symptoms of doughtiness, but the soil is often relatively
moist.