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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 |
