Capacitance is a method of measuring the amount of water in soil through its capacity to transmit electromagnetic waves or pulses.
In effect, the soil is placed between two electrical plates and when voltage is applied to these plates a frequency is measured. This is then converted using a calibration equation into mm of soil moisture per metre.
There are several types of capacitance system available.
The distinguishing feature of these systems is that they are able continuously log readings at close time intervals. Different products are available for:
The readings can either be downloaded to a computer via automated transmission systems, by phone, or by visiting each site to download them manually.
Different systems support a different number of sites and depth intervals. Check with the distributor to ensure the system meets your requirements.
Portable capacitance probes measure soil in much the same way as previously described. The main difference between this and a permanent system is that readings must be taken manually, using the probe which has just one sensor on the end.
The probe is swiped down the profile (via an access tube) and takes readings at 10cm intervals. The information collected can be displayed as chart giving a graphic display of the soil moisture content at different depths down the profile.
Depending on the system you choose, the data can either be viewed in the field, on the display unit, or downloaded to a computer.
Speak to an irrigation consultant or your product distributor to find out how best to meet your requirements. We have developed a range of factsheets to assist you with irrigation management. See the links related below.