Soil Moisture Measurement Techniques and Equipment from Van Walt Ltd
For over 25 years Van Walt has been providing soil and groundwater monitoring equipment to the environmental, educational and agricultural research communities. Our wide range of equipment includes: hand augers, manual augers, window samplers, penetrometers, soil sampling equipment; sampling pumps, peristaltic pumps, bailers, tubing, filters, multimeters, water level meters and more.
Soil Moisture Measurement
There are many ways to measure soil moisture. The most accurate is to take a volume of soil, weigh it, (air) dry it and then weigh it again. The impracticality of this method has led to the development of other techniques.
The best known was the neutron probe which used a radio active source lowered into the soil by means of an aluminium access tube. Pulse bounces were counted by the device to record soil moisture very accurately. With its demise, on safety issues and the fact that it was incapable of measuring top layers, TDR (Time Domain Reflectrometry) became a safe replacement and, although accuracy was not quite as high, it is a very credible alternative which almost matches the accuracy and repeatability of the neutron probe.
TDR measures the 'dielectric constant' of a material to determine the moisture. The dielectric constant is a complex quantity with a real number that characterises the moisture and with an imaginary component as a measure for energy loss and electrical conductivity. Both parts depend mainly on frequency so that the measuring frequency of an electromagnetic technique is a decisive criterion.
TDR is the favoured tool for researchers and very recent technology has allowed TDR moisture sensors to be manufactured which are priced to almost match the less accurate capacitance, frequency domain based alternatives.
At Van Walt we distribute the award winning TRIME TDR range of systems including the new PICO-BT Bluetooth Module.
Find out more about soil moisture measurement equipment