EQUIPMENT

  1. YSI model 34 Conductance-Resistance Meter
  2. Conductivity cell

REAGENTS:

  1. 0.01 M KCl: weigh .7456 g KCl into a 1 liter volumetric flask.
    Dissolve and dilute to volume with deionized water and mix well.

EXTRACTION PROCEDURE:

  1. Weigh 50 g of soil into a 250 mL beaker.
  2. Add 100 mL deionized water.
  3. Stir well and let stand for 1 hour.
  4. Filter using Whatman #42 paper. The filtrate may be turbid.
  5. Transfer the filtrate into a test tube which can accommodate the conductivity cell.
  6. Prepare one duplicate sample and one quality control sample with each set of samples analyzed.

DETERMINATION OF THE CELL CONSTANT

  1. Depress the conductance push button.
  2. Depress the range switch 0-2 m mhos.
  3. Rinse the conductivity cell 3 times with 0.01M KCl solution.
  4. Place the cell into a 0.01M KCl solution taking care to be sure that no air bubbles remain inside the cell.
  5. Record the m mho reading
  6. Calculate the cell constant using the following formula:
1.413 ÷ m mhos reading = cell constant

INSTRUMENT OPERATION

  1. Depress the conductance push button.
  2. The instrument has 7 push button range switches.
    1. 0-2 mhos
    2. 0-20 mhos
    3. 0-200 mhos
    4. 0-2 m mhos
    5. 0-20 m mhos
    6. 0-200 m mhos
    7. 0-2 mhos
  3. Depress the 0-2 mho push button.
  4. Place the conductivity cell into a soil filtrate, taking care to make sure that no air bubbles remain on the inside of the cell. If a 1 appears in the left portion of them, meter display and the other digits are blank, the conductance of the filtrate is greater than 2 mhos. Select the next higher range switch. Continue in this fashion until numbers appear in the meter display.
  5. Record the meter reading.
  6. Rinse the conductivity cell with deionized between each soil sample analysis.

CALCULATION

  1. Meter Reading × Cell Constant = conductivity
  2. Record values as mhos/cm.
  3. If the range switch is in the mho range, use the equation in 1 above.
  4. If the range switch is in the m mho range, multiply the value obtained in 1 above times 1000.
  5. If the range switch is in the mho range, multiply the value obtained in 1 above times 1,000,000.

QUALITY CONTROL

  1. Values on the duplicate samples must agree within 20% of the average of the two values.
  2. Values on the quality control sample must lie within the established limits for this sample.

REFERENCES

  1. Bower, C. A. and L. V. Wilcox. 1965. Soluble Salts. In C. A. Black (ed). Methods of Soil Analysis. Soil Sci. Soc. Amer. pp 933-951.
  2. Jackson, M. L. 1958. Soil Chemical Analysis. pp 227-255.