Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 285

in soils causes plants to prematurely suffer drought stress even though substantial
water may be present in the soil. Osmotic potential is a direct result of the combined
concentrations of dissolved Na, Ca, K, and Mg cations, and Cl -1 ,SO 4 -2 ,HCO 3 -1 ,
and CO 3 -2 anions which are common constituents in salty water.

8.3.2.8 Unit of EC

The SI unit of conductivity is “Siemens” (symbol “S”) per meter. The equivalent
non-SI unit is “mho” and, 1 mho = 1 Siemens. Thus,

=

1 mmho/cm 1 dS/m

(one milli-mho per centimeter

=

One deci-Siemen per meter)

8.3.2.9 Unit Conversion

Conductivity to mmol per liter :
mmol/l EC (EC in dS/m), for irrigation water and soil extracts in the

range 0.1-5 dS/m.
Conductivity to osmotic pressure in bars :
OP

= 10 ×

EC (EC in dS/m), for soil extracts in the range of 3-30 dS/m.
Conductivity to mg/l :
mg/l

= 0.36 ×

= 0.64 × EC (in μ mhos/cm)

= 640 × EC (in dS/m), for waters and soil extracts having conductivity up to 5

dS/m
mg/l = 800 × EC (in dS/m), for waters and soil extracts having conductivity

>5 dS/m
mmol/l (chemical analysis) to mg/l :
Multiply mmol/l for each ion by its molar weight and obtain the sum.
Ions to EC:
Total sum of cations and anions (meq/l)

= 10 × EC (dS/m), 0.1 < EC <

5.0 dS/m.

8.3.3 Diagnosis of Salinity and Sodicity

Proper diagnosis is critical to any successful problem correction. The first step
toward management of any salt-affected soil is an assessment of the soil includ-
ing the soil profile. Effective management of salinity or sodicity problem requires
correct diagnosis of the problem. A salt-alkali soil test should be established to see
whether the soil is saline, sodic, saline-sodic, or not affected by salts. An examina-
tion of the soil profile along with soil survey information will help determine soil
permeability characteristics, which are important in leaching salts. In some cases,
it may be necessary to facilitate drainage using tile drains or open ditches to allow
successful reclamation.