Frequently Asked Questions
- 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.
- 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.
- 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.