Published by Australian Academy of Science
Glossary | Monitoring the white death – soil salinity

electrical conductivity. When a voltage is applied across a substance, an electric current will only flow if the substance conducts electricity. When salts dissolve in water, ions are formed and the solution (the electrolyte) will conduct electricity. As a general rule, the higher the concentration of ions in solution (ie, the higher the salt concentration) the better the solution conducts electricity; in other words, its electrical conductivity increases. Electrical conductivity is often expressed in units such as deciSeimens per metre (dS/m). Rain water, for example, has a conductivity of 0.02-0.05 dS/m, while sea water has a conductivity of 50-60 dS/m.

electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).

parent rock. The original rock from which a soil has come. For example, sandstones are often the parent rocks for sandy soils. Except where there is extensive weathering, the composition of the mineral fraction of the soil generally indicates the nature of the parent rock underneath. Layers of soil and subsoil lie on top of the bedrock.

soil profile. Where soil has been cut through vertically, such as along a roadside embankment, you may see that it has various layers of different textures and shades. This is called the soil profile. The top layer, called the A horizon, is the one where most roots are, where most biological activity occurs and where organic matter accumulates. Water washes clay particles down out of this horizon.

In the next layer – the B horizon – clay particles and soluble substances washed down from above tend to accumulate. Below that is the C horizon, or parent rock. The type of parent rock can affect the fertility and structure of the soil that develops above it.