Use these instruments to measure the conductivity of your soil. Soil conductivity is related to the concentration of dissolved salts and nutrients, so measuring conductivity helps in the analysis of your soil.
"Electrical conductivity determines the electrical current between two points (electrodes) of different voltage potentials in a liquid. The conductivity increases as the amount of salt, acid or base contained in a solution increases. Conductivity is measured in units of mS/cm. The scale for water-based solutions starts with pure water (conductivity equals 0.05 µS/cm at 25 °C) and ends with a basic solution of 1.0 mS/cm (e.g., potassium solutions). Potable or surface water has a conductivity value in a range from 0.1 to 1.0 mS/cm.
Conductivity is measured using a measuring cell which consists (in the simplest case) of two similar electrodes. An AC voltage is applied to an electrode and this causes the ions in the solution to move in relation to the electrode. More current flows between the electrodes when more ions are contained in the solution. Using this measured current, the meter calculates the conductance of the solution and then, based on the cell specification, the actual conductivity value."