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Analytical Methods

Chemical Analyses: Electrical Conductivity

Salinity is a soil property referring to the amount of soluble salt in the soil. It is generally a problem of arid and semiarid regions. Electrical conductivity (EC) is the most common measure of soil salinity and is indicative of the ability of an aqueous solution to carry an electric current. Plants are detrimentally affected, both physically and chemically, by excess salts in some soils and by high levels of exchangeable sodium in others. Soils with an accumulation of exchangeable sodium are often characterized by poor tilth and low permeability making them unfavorable for plant growth.

By agricultural standards, soils with an EC greater than 4 dS/m are considered saline. In actuality, salt-sensitive plants may be affected by conductivities less than 4 dS/m and salt tolerant species may not be impacted by concentrations of up to twice this maximum agricultural tolerance limit. Thus, the reclamation scientist must exercise care in interpretation of salinity standards. Salinity should be defined in terms of the predisturbance land use potential, the proposed postdisturbance land use, and the plant species to be seeded on the site (Munshower, 1994).

The saturation paste extract method is the most commonly used laboratory procedure for determining conductivity. The soil sample is saturated with distilled water and mixed to a paste consistency. After standing for one hour, the salts will dissolve and the electrical conductivity of water extracted from the paste is measured using electrodes. A variant of this method involves measuring conductivity from a 1:2 soil-water mixture after 0.5 hours of shaking. The latter method takes less time but often is not as well related to the soil solution as is the saturation paste extract method. Calibration of the electrodes with a standard solution is necessary before measuring the conductivity of the sample. Once the soil sample is in a soil-water mixture, it can be measured the same way as for aqueous samples. For more info on measurement of conductivity, see the aqueous electrical conductivity section. For details on the methods used to measure conductivity, see methods 2, 3a, and 72 (Agriculture Handbook No. 60, 1969).

 

Chemical Analysis | Physical Properties

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