Frequently Asked Questions
- Water potential - T8 Tensiometer - T4 Tensiometer - T5 Tensiometer How does a tensiometer deal with partially saturated soils?
A tensiometer is able to measure positive pressures along with the water potential measurements. If you use the right tensiometer, you can actually have a very good measurement near saturation.
- TEROS 21 - TEROS What does the -9990 error code or “Sensor value is temporarily out of range” mean?
Water potentials below -2,000 kPa exceed the detection limits of the TEROS 21. When water potential is below -2,000 kPa, the TEROS 21 will report an error code (-9990), and an error message will appear (Sensor value is temporarily out of range).
- TEROS 21 - TEROS Why does the TEROS 21 now only read down to -2000 kPa?
To increase TEROS 21 dry end accuracy and reduce temperature sensitivity in the plant available range, the ceramic formula and sensor calibration have been improved, limiting the dry end measurement to -2000 kPa. This change is also to optimize the sensor’s performance in the plant available water potential range. Sensors manufactured after 8/1/2019 with serial numbers T21-00010000 and up will have this new measurement range.
- TEROS 21 - Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - T8 Tensiometer - T4 Tensiometer - T5 Tensiometer - LABROS How can you measure capillary water potential?
Capillary water potential is tied to matric potential. So if you are measuring matric potential with a tensiometer or a TEROS 21, you are essentially measuring the effect of the capillaries or those different pore sizes. You can also use the HYPROP. The WP4C will also work assuming the soil has a negligible osmotic potential.
- TEROS 21 - Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - T8 Tensiometer - T4 Tensiometer - TEROS - T5 Tensiometer Do matric potential sensor readings include osmotic potential?
This depends on what type of instrument you are using to measure the potential. For example, tensiometers, granular matric sensors, and the TEROS 21 ONLY measure matric potential. So these sensors are blind to osmotic potential. Laboratory instruments like the WP4C measure both osmotic and matric potential. But in terms of field sensors, there aren’t any that give both components.
- TEROS 21 - Water potential - Soil Moisture Sensor - GENERAL - T8 Tensiometer - T4 Tensiometer - T5 Tensiometer How can you measure kPa or MPa? And what tools can you use for container production?
kPa and MPa are really just a preference. You convert between the two by moving the decimal point. In containers, you can use tensiometers which are highly accurate in the wet range but not in the dry range. Matric potential sensors such as the TEROS 21 also work well. They aren’t as accurate as a tensiometer in the wet end, but they give you a better range and require less maintenance.
- Soil Moisture Sensor - TEROS 11 - Volumetric Water Content - TEROS 12 - GENERAL - TEROS What tools can I use to measure soil moisture along a soil profile of 40cm depth?
- Soil Moisture Sensor - ECH2O 5TE - Volumetric Water Content - TEROS 12 - GENERAL - GS3 What will measuring electrical conductivity give you a metric of versus VWC?
EC can give you the solute concentration of the soil, but is trickier to interpret than VWC since the VWC can be a confounding variable.
- TEROS 21 - Water potential - Soil Moisture Sensor - TEROS 11 - Volumetric Water Content - TEROS 12 - GENERAL - GS3 - TEROS What are important considerations when thinking about measuring water content and water potential in peatlands (with organic soils)?
Variability of your substrate is a big one. There is a lot of variability in soils as well, but we have better mechanisms to capture and account for variability in mineral soils. Good substrate-to-sensor contact is critical and trickier to accomplish (good installation), but it is achievable. You will most likely require a custom calibration for water content.
- Soil Moisture Sensor - ECH2O 5TE - TEROS 11 - ECH2O 5TM - Volumetric Water Content - TEROS 12 - GENERAL - ECH2O EC-5 - TEROS What is the difference between the FDR method and the capacitance method of VWC measurement? Are they the same?
They are technically not the same. For the strictest technical accuracy, FDR makes a frequency scan and capacitance measures the charge time of a capacitor. From a practical standpoint there is little difference in the performance.
- TEROS 21 - Water potential - Soil Moisture Sensor - TEROS 11 - Volumetric Water Content - TEROS 12 - GENERAL - TEROS Would you agree that with the impact of soil moisture on the atmosphere, measuring water content alone is not enough?
It depends on your specific goals. If you are studying the impact of soil water on atmospheric impact then you would need water potential. There are plenty of cases where water content alone is sufficient if you also have information about your soil.
- TEROS 21 - Soil Moisture Sensor - GENERAL - TEROS If I use the TEROS 21 to measure soil water potential when planning irrigation, do I need to know the soil type?
No. With the TEROS 21 you just need to know the matric potential limits of your plants, and you do not need to worry about soil type.
- TEROS 21 - Water potential - Soil Moisture Sensor - WP4C - HYPROP - GENERAL What is matric potential?
Matric potential is the force that would need to be exerted to move a water molecule from the surface of a soil particle. For example, a matric potential of -100 kPa would require a force of -101 kPa to pull that water molecule off of the soil particle. It is one component of the total water potential. Learn more about the different components of water potential here.
- TEROS 12 When installing near a rock, would the soil “look” drier than the rest of the soil if the rock is more of an erratic?
It won’t just look drier, it probably is drier on a volumetric basis. The rock does not have the pore space of soils for water to displace, and therefore the soil area with the rock in it can contain less water. The rock is probably more dense than soil because it has fewer pores, but there needs to be a pretty large change in density to have a significant effect on the sensors.
- TEROS 12 What would data look like if you installed next to a rock, given that rock dielectric is different?
The dielectric of rock isn’t necessarily different than that of the soil. The dielectric of the soil is probably strikingly similar to that of the parent material in soils that are derived from the parent material of their locale. And even loess is probably pretty close. Rocks (or anything) with a high iron content may be problematic and require a custom calibration.
- TEROS 12 METER offers a custom calibration for saline conditions, but as you continue to irrigate with saline water, the soil becomes more saline. Because there will be spatial variability in that salinity, do you need to re-calibrate periodically?
Our sensors are robust to changes in salinity up to a point. Beyond about 8 dS/m saturation extract EC, you will require a custom calibration. This topic is complex and deserves its own seminar, so please contact email@example.com if you have further questions.
- TEROS 12 If you install a TEROS 12 sensor with the tool and bend one of the sensor pins, is it easy to detect that by looking at the data?
This type of occurrence should be extremely rare since the application of force of the tool is so controlled. A small bend in the prongs should not affect the output of the probe. The probe will most likely break before presenting an inaccuracy.
- TEROS 12 With the TEROS Borehole Installation Tool, how moist/soft does the soil have to be so that the sensor can be driven into the soil?
So far, we have not found a soil too hard for the installation tool to install sensors. We installed TEROS 12’s in soils that were 60% – 70% clay in August 2017. There were no problems with the installation. However, as you install, be on the lookout for rocks.
- TEROS 12 What are the rental options for the Borehole Installation Tool? Does METER send it to us, and then we return it?
METER will rent the TEROS Borehole Installation Tool to you for a monthly fee if you only need it for a few weeks to install your sensors. The $500.00 fee includes shipping and a return label to send it back to us when you are done. Please contact firstname.lastname@example.org if you have any questions.Below are the options for renting the TEROS Borehole Installation Tool:Standard rental for orders <50 Sensors: $500/monthIf rental is returned within two weeks, we will refund $200 of the rental.For orders >50 sensors: $150/monthOrders >100 sensors: Free 1-month rental of tool
- GS1 - TEROS 12 - GS3 - TEROS What is the volume of influence comparison for the GS1, GS3, and TEROS 12?
See our volume of influence article for a comparison of all METER soil moisture sensors.
- TEROS 12 - TEROS Can the TEROS 12 be installed in coir slabs?
The TEROS 12 can be used in COIR slabs. We provide a soilless media calibration that is based on measurements in potting soil, COIR, and Perlite.
- TEROS 12 - TEROS Do TEROS 12 sensors communicate with third-party systems?
The TEROS 12 uses the SDI-12 communication protocol. As long as the system is capable of SDI-12 communication and supplying the necessary 4-12 V power supply, they should be compatible.
- TEROS 12 - TEROS What is the cost of a complete TEROS 12 setup, for example, sensors, data loggers, installation tool, 4″ auger, data plan, etc…?
The installation tool has both a rental and a purchase option, and the number of sensors/data loggers needed will vary for each application. Contact customer support to learn about options customized to your specific application.