Are there water potential case studies for plants and turf available?
There are a lot of case studies about different types of plants, specifically about optimal water potential ranges. There was a paper done by Dr. Sterling Taylor on this topic, and there are also some studies being done by BYU scientists with in situ water release curves in turfgrass. One of our scientists wrote an article (find it here) and gave a webinar (find it here) about some of the turfgrass work being done at BYU.
What sensor might be appropriate in more arid environments when the soil water potential might be very low much of the year?
One of the better sensors for measuring in really dry conditions is a thermocouple psychrometer. The problem is they are not as commercially available and difficult to find. But if you can find one, they are a really useful tool for arid environments.
Can the relationship between soil moisture and water potential in the sensor range of accuracy be used to infer water potential from soil moisture readings in drier conditions?
This is actually a common approach taken by many people. You can try and develop that relationship in situ and infer what the drier condition water potentials are. There are functions available such as different van Genuchten functions to try and fit those data.
How is the sensitivity of capacitance sensors to the resistivity of pore water (chemical composition)?
Capacitance sensors will be affected by salt concentrations in soils when they become higher. Typically, we start seeing issues when the saturated extract EC is higher than 3 dS/m. This can be hard to correct for since the sensors don’t measure EC. If you had another sensor nearby measuring the bulk EC of the soil, you could potentially make a correction for this.
How is the temperature sensitivity of the capacitance method in the wet side (between 20 to 50 C)? Are there any compensation equations for your sensors?
The temperature sensitivity in the wet range for the TEROS 21 is low. Because there is more water in the ceramic, the temperatures swings don’t have much of an impact on the measurement. I would expect the readings between -10 and -300 kPa to have low sensitivity to that temperature range. Having said that, there is a great paper on temperature compensation for the TEROS 21 that works well. Here is the reference: L. Walthert and P. Schleppi (2018). Equations to compensate for the temperature effect on readings from dielectric Decagon MPS-2 and MPS-6 water potential sensors in soils. J. Plant Nutr. Soil Sci. 2018, 000, 1–11 (article link).
Are water potential sensors available that measure at 2" and 5" at the same time?
Currently, there is not a profile-type water potential sensor. The only way would be to place individual sensors at the desired measurement depths. A profile probe could be a powerful tool for this measurement and is something we may approach in the future.
Is there a paper you can refer me to concerning the effects of digging a trench on the soil at a site?
I don’t have a specific paper to refer to on this topic. The concern with large trenches is the way it affects water movement through the soil near the sensor. Depending on how the trench is repacked you can wind up with preferential flow paths which will result in faster water migration through the soil profile. For more information on this topic, see our article: "5 Ways Site Disturbance Impacts Your Data."
Which is the best sensor for measuring water potential lower than -1 atmosphere for research purposes?
For water potential below -1 atm (-100 kPa), a solid matrix sensor like the TEROS 21 is going to be more appropriate.
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).
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.
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.
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.
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.
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.
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.
If I use the TEROS 21 to measure soil water potential when planning irrigation, do I need to know the soil types?
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.
What is the 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.


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