Conductivity and conductance of soil

1. SHREE MALLIKARJUN COLLEGE CLASS: SYBSC
Safety: Refer to MSDS of KCl. Dr. Mithil Fal Desai
Aim: Determination of conductivity of soil sample.
Chemical/Apparatus: Potassium chloride/Beakers, funnel, flask and glass rod.
Instrument: Conductivity cell
Theory: Soil electrical conductivity (EC) is a measure of the ability of soil to carry electrical
current. Generally, the conductivity of soil ranges from 110-570 milliSiemens per meter (mS/m).
Lower conductivity values indicate insufficiency in nutrients and very high levels reflect an excess
of the nutrients. It is one of the important parameters for determining the quality of the soil. The
conductivity measurement of soil samples can help assess the contamination of surface and
groundwater.
The higher conductivity reveals the presence of negatively charged ions like chlorides (Cl-
),
sulphate(SO4
2-
), nitrites (NO2
-
), nitrates, (NO3
-
) and positively charged ions like sodium (Na+
),
ammonium (NH4
+
), potassium (K+
), calcium (Ca2+
), magnesium (Mg2+
), hydrogen (H+
), iron (Fe2+
/Fe2+
), copper (Cu2+
), zinc (Zn2+
) and manganese (Mn2+
) which are beneficial to plants.
Procedure:
i) Calibrate the conductivity cell
Refer to the instrument manual.
ii) Determine the cell constant.
Rinse and dip the conductivity cell 0.1N KCl and record the conductance observed. Note down
the temperature. Wash the conductivity cell with distilled water and measure the conductance for
0.01 N KCl.
iii) Measure the conductivity
a) Measure the conductance of distilled water by dipping the conductivity cell in distilled water.
b) Take 1 g of soil sample in a 100 mL beaker and add 100 mL of water. Stir the suspension for
30 min and filter. Rise and dip the conductivity cell in the filtered solution. Record the conductance
observed. Note down the temperature. Clean the conductivity cell after use.
Observations:
1. Room temperature =____ ◦C.
2. Cell constant =_____ per m
3. Conductance of distilled water =______ S.
4. Conductance of soil filtrate =______ S.
Result: Conductivity of soil sample is =______S/m.
Further Reading
Experiments in Applied Chemistry, S. Rattan, S. K Kataria and Sons.