Salinity in Soil
Measuring the conductivity of water samples to determine if water "runoff" from soil is more or less likely to conduct electricity.
PASPORT Conductivity Sensor (PS-2116)
Lab Summary
Students will measure the conductivity of water samples, both before and after being mixed with soil samples, to determine if water "runoff" from soil is more or less likely to conduct electricity.
Conductivity is a measure of the ability of a substance to conduct an electrical current. A solution’s conductivity is affected by the presence of inorganic dissolved salts such as chloride, nitrate, sulfate, and phosphate anions (negatively-charged ions) or sodium, magnesium, calcium, iron, and aluminum cations (positively-charged ions). Organic compounds like oil, phenol, alcohol, and sugar do not conduct electrical current very well and therefore have a low conductivity when in aqueous solution. Because conductivity is dependent upon solute concentration, conductivity measurements are a good indication of the concentration of dissolved solids in aqueous solution. Conductivity is also affected by temperature: the warmer the solution, the higher the conductivity.
In natural settings, salt content may be high in both soil and water. River waters, for example, show a wide range of salinities due to different soil types, geological structures, and the extent to which they are influenced by inflows of saline groundwater. Problems arise when the natural balance of salinity in the landscape changes. Salinity is a major threat to surface and groundwater resources. Depending on the level of salt content in soil, plant growth may be impacted. High levels of salinity in rivers may limit water use for irrigation, agriculture, stock watering and domestic water supplies. Salinity can also affect freshwater aquatic flora, fauna and riparian vegetation. In urban areas, salinity reduces the lifespan of domestic and industrial equipment, leading to higher maintenance costs and greater use of cleaning products.
For aqueous solutions, the most commonly used units of measurement for conductivity are microsiemens/centimeter (µS/cm) and millisiemens/centimeter (mS/cm). See "Teacher’s Hints" for more information about these standard units.
Published: February 2002
Downloads
- Salinity in Soil - PASPORT (56 KB, .zip)
Includes setup, procedures and Datastudio file
- Salinity in Soil - ScienceWorkshop (56 KB, .zip)
Includes setup, procedures and Datastudio file
Here's What You Need
U.S. Educator prices shown.
probeware (PASPORT System)
PASPORT Conductivity Sensor (PS-2116A) - $110
Utilizes platinum probes for greater range and improved accuracy in high & low concentrations.
Xplorer GLX (PS-2002) - $349
The Xplorer GLX is a data collection, graphing, and analysis tool designed for science students and educators.
Probeware (ScienceWorkshop System)
10x Conductivity Sensor (CI-6739A) - $145
Used to explore the effect of temperature and concentration on the electrical transport properties of aqueous solutions.
750 Interface, USB (CI-7650) - $679
The 750 Interface allows students to measure force, temperature, pressure, angular velocity, acceleration, current, and magnetic field with a built-in function generator and oscilloscope mode.
Other Materials
- Soaker bottle for Conductivity Sensor
- Distilled water (or tap water if distilled water not available)
- Sample of dirt from school yard
- Sample of potting soil from local nursery or retail store
- Five 500-mL beakers, and a stirring rod
- Two coffee pot filters
- Wash bottle for rinsing sensor
