Measuring water in soil - capacitance
- Fact sheet
- August 2015
What is capacitance?
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.
Permanent systems
The distinguishing feature of these systems is that they are able continuously log readings at close time intervals. Different products are available for:
- permanent plantings such as tree crops and vines
- fast growing, shallow root-zone crops.
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.
Advantages
- components are modulated enabling a custom-designed system
- minimal soil disturbance during installation
- multiple and customised sensor depths (0.5 – 5.0m)
- software available
- no labour input for readings
- minimal maintenance required
- remote telemetry available
- integration with other products.
Disadvantages
- more expensive than many other systems
- small sphere of influence of around 10cm radius
- installation in rocky/sandy/shallow soil can be difficult
- access tubes need to be installed by qualified technicians.
Portable systems
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.
Advantages
- minimal soil disturbance during installation
- software available
- minimal maintenance required
- can service a large number of sites
- readings taken quickly with one swipe.
Disadvantages
- requires frequent labour for readings
- manual downloading of readings is required
- small sphere of influence – around 10cm radius
- installation into rocky/sandy/shallow soil can be difficult
- access tubes need to be installed by qualified technicians.
More information
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.
Related links
- Approvals for irrigation development in the River Murray high salinity impact zone (fact sheet)
- Cover crops to prevent wind erosion (land under centre pivot irrigation) (fact sheet)
- Cover cropping for land under centre pivot irrigation (fact sheet)
- Gypsum blocks for irrigation management (fact sheet)
- Neutron probes and soil moisture (fact sheet)
- On-Farm Irrigation Efficiency Program wrap up (fact sheet)
- Wind erosion (land under centre pivot irrigation) (fact sheet)