Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 289

Table 8.5 Test required for different problem identification

Tentative problem Test required

Suspect a salinity or sodicity problem Soil EC, pH, and SAR

TDS, EC, SAR, Na + ,Cl - ,B,HCO 3 - Suspect poor quality irrigation water

A salinity problem exists and want to monitor or
calculate leaching requirement

Soil EC, irrigation water EC, consider
spatial mapping of field EC

A sodicity problem exists and want to calculate
gypsum requirement

CEC, ESP and/or SAR, lime estimate

8.3.3.3 Determination of Intensity of Salinity and Sodicity Hazard

Irrigators should determine the potential salinity and sodium hazard of their water
and soil before planning crop cultivation or any successful management planning.
The salt content of a soil can be estimated by measuring the electrical conductivity
(EC) of the saturated soil extract.

Estimation of Salinity

Salinity is estimated by measuring electrical conductivity, EC. The ability of a solu-
tion to carry current is called electrical conductivity. The electrical conductivity of
a solution is proportional to its soluble salt content (In an aqueous solution, the EC
increases with the concentration of ions and hence the concentrations of total dis-
solved salts). The more salts in the sample, the greater is its electrical conductivity.
Similarly, the lower the EC reading, the lower the salinity. The severity of salin-
ity or sodicity is based on the value of EC or ESP, as described in the preceding
section.

Measuring EC

Take a sample of soil, add enough water (salt-free) to the soil sample to completely
saturate it, stir it for some time, and extract water from the saturated soil using
a vacuum pump. Then measure the electrical conductivity (EC) of the saturation
extracts using an EC meter or other type of instrument. In the absence of vacuum
pump, some recent devices (handy EC meters, under different brand/commercial
name) allow inserting and measure EC directly in the soil saturated paste.
Available hand-held devices are much quicker and easier than sending away a
soil sample to a laboratory.

Measuring/Estimating ESP, SAR

Estimation of ESP

A second important measure is the amount of exchangeable sodium, determined
by extracting the soil with 1 M ammonium acetate and measuring the amount of
sodium in the extract. The results of this extraction must be corrected for soluble