In agriculture and science, electrical conductivity (EC) is an excellent way to measure water, soils and fertilisers using a handheld meter or desktop device. Fundamentally, it is possible for them to do this by measuring the dissolved salts in solutions and hence the salt content of soil or water; more salt will mean a higher conductivity of the solution. Usually a high conductivity reading from your meter will mean that your plants will be suffering. In some cases a high salinity will result in the edges of leaves being 'burnt' or even wilting and death.
The limitations of a conductivity meter are however relatively important. While you will be able to find the salt content, no indication of which salts are causing the problems will be given. It may purely be down to your own deductions to find the problems although with detailed laboratory testing, rather than the handheld meter it will be possible to find the problems in your soil and water. It is usually worth taking a variety of readings with your meter of the water, soil and potting compost; this way through a process of elimination it is easy to find a solution to your plant's problems.
Conductivity is measured in deci-Siemens per metre or dS/m, as well as this measurement your meter will most likely measure micro-Siemens per centimetre and milli-Siemens per centimetre. Siemens are normally known as ohms, an electrical resistance measurement. Naturally in the agricultural world it is measured with an added distance element rather than just electrical conductivity or resistivity. Predominantly this uses two electrodes a known distance apart in the sample soil or water.
Unfortunately the readings given by your conductivity meter will be affected by temperature as ions and the way in which they react with each other are affected by temperature. It is estimated that conductivity in fact changes about two percent per degree in Celsius so a note of the temperature needs to be made at the time of taking readings. In addition, it is advisable to keep your samples to as close to twenty five degrees Celsius as possible in order for accurate conductivity results.
Salt concentration in science and agriculture is also measured in total dissolved salts (TDS) in parts per million. There are meter solutions to finding this figure but it is also possible to find this by weighing samples before and after evaporation. It differs from conductivity in the way that it gives the total mass of the salts rather than purely their ability to conduct electricity.
Fundamentally there are two types of conductivity meter on the market today. Portable models normally use a probe rather the more expensive and accurate bench top systems. The handheld conductivity meter is usually quite affordable and helpful for field measurements. There are however not as accurate as the bench top variety and are prone to breaking after extensive use. Waterproof models may cost a little more but on the whole are more worthwhile as the meter will last for a longer period of time. As with most conductivity meter systems, calibration is essential.
Calibration of your conductivity meter should occur before every use in order to achieve accurate results. This is a plainly simple task however; all you must do is to take a measurement of a solution with a known conductivity. This way, by adjusting the screw at the back it is possible to calibrate the meter and take accurate readings of solutions with unknown conductivity.
The conductivity meter is used in all manner of scientific and agricultural situations giving readings of accuracy and knowledge to advance production and efficiency. Today it is arguable that the agricultural industry would be unrecognisable without their use as they have advanced farming and crop production immensely.
science expert Thomas Pretty looks into how the conductivity meter has changed the way the agricultural industry operates.