Determination of Soil Electrical Conductivity
   
  S. D. Carroll, C. G. Herron, D. C. Lafex  
  University of Arkansas Soil Testing and Research Laboratory  
  P. O. Drawer 767  
  Marianna, AR 72360  
  Phone 870-295-2851 email soiltest@uark.edu  
 
   
  Contents
 

Purpose and Background
 
Procedure
 
Quality Control Assessment
 
References
 

Purpose and Background
  The purpose of the electrical conductivity analysis is to determine the concentrations of soluble salts. All soil has some water soluble salts which include essential nutrients for plants to grow. If the water soluble salts exceed an certain level then harmful effects on plant growth occur. The common unit of measurement for electrical conductivity is microsiemens/centimeter formerly micromhos/cm.
   
 

Procedure
 

1. Scoop 20 g of soil sample into a 3 1/2 oz solo cup in the Styrofoam sample rack, leaving the first row of cups empty. These will be filled with Reverse Osmosis(RO) water and used as a rinse station.

2. Using the dispenser, add 40 ml of RO water to each sample cup.

3. Vigorously stir each sample with a glass, stirring rod.

4. Allow sample to stand for 15 minutes.

5. Insert racks into place on XYZ Table "Robbie #3"

6. Make sure the cell constant for the Orion meter is set to 0.475. Also make sure you run the Electrical Conductivity before running pH.

7. Analyze the samples using the "Robot Table Data Acquisition Program"
   
 

Quality Control Assessment
 

This laboratory participates in the North American Proficiency Testing Program(NAPTP) operated by the Soil Science Society of America for all soil analyses including EC.

Every 12th sample in an analysis batch is one of the following:

Low QC (RO water)- EC must read below 4

High QC (1.3(10-3)M KCl)-EC must read between 90-100.

Check Soil- EC must read within the limits shown on the Quality Control sheet for that batch of check soil.
 
 
Modifications: We modified the equilibration time from 30 minutes to 15 minutes.
 
 

References
  Donahue, S. J. 1983. Determination of specific conductance in supernatant 1:2 soil: water solution. p. 8-14. Reference Soil Test Methods for the Southern Region of the United States. Southern Cooperative Series Bulletin 289. University of Georgia College of Agriculture Experiment Station. Athens, GA.
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