Water Potential 201: Getting the Most from Each Measurement

Knowing your soil’s optimal water potential levels and taking measurements over time is crucial to understanding the health of your plants and to predict soil water movement. But why stop there? While water potential is powerful on its own, there is even more insight to be gleaned when it's applied to other calculations.
In this 30-minute webinar, research scientist and METER’s Director of Scientific Outreach, Leo Rivera, dives deeper into soil water potential, applications of the measurement, and how to make sure you are making the most of the tools available. Within this webinar he will discuss:
- Using water potential data to infer other processes and properties in soil
- The resources available to determine the right water potential ranges for your plants
- How to choose the right water potential sensor for particular applications
- How to minimize the possibility of preferential flow
- The difference between soil water potential and plant water potential and when to measure each
- And more

2. WATER POTENTIAL 201
Getting the most from each measurement
Leo Rivera, MS
Director of Scientific Outreach

3. Two variables necessary to describe state of matter or energy in environment
•Extensive variable –describes the extent or amount of matter or energy
•Intensive variable –describes the intensity or quality of matter or energy
Extensive Intensive
Volume Density
Water Content Water Potential
Heat Content Temperature
Extensive vs. Intensive Properties

4. Energy required, per quantity of water, to transport
an infinitesimal quantity of water from the sample
to a reference pool of pure, free water
Water Potential
Definition

5. Applications of
Water Potential Data

6. Directly measuring water availability
How do I know what is the ideal range for my plant?
Generating soil moisture release curves
Lab vs field?
Water movement in soil
Can I measure hydraulic conductivity?
Applications of Water Potential Data
How can we best utilize this measurement?

7. Soil Moisture Release Curves
•Soil moisture release curves are
typically generated in the lab
•How well do these curves apply
to the field?
•Can we generate good curves
using field data?

8. Soil Moisture Release Curves
Field measurements
Sensors:Water potential/water content(2 depths – 8 cm and 15 cm)

9. Soil Moisture Release Curves
Field measurements

10. Soil Moisture Release Curves
8 cm depth 15 cm depth
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.34
0.36
0.38
0.40
-1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00
volumetric water content (m3/m3)
Matric potential
Retention curve (8 cm)
0.20 0.22 0.24 0.26 0.28
0.30
0.32
0.34
0.36
0.38
0.40
-1.50-1.00-0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00
volumetric water content (m3/m3)
Matric potential
Retention curve (15 cm)

11. Water potential is the driving factor in water movement in soil
•Water moves from high to low potentials
Can we use in-situ data to also measure hydraulic conductivity?
Water Movement in Soils
Water fluxes & unsaturated hydraulic conductivity

12. Identifying Ideal
Water Potential Ranges

13. Determining the appropriate water potential range for your plants involves understanding their specific water needs, which can vary widely
depending on the species and environmental conditions. Here’s a structured approach to figuring it out
1. **Research Plant Species**: Different plants have different water requirements. Research the specific plant species you have or are
interested in growing. Plant databases, gardening books, or university extension websites often provide detailed information on the water
needs of various plants.
2. **Consider Native Habitat**: Plants often thrive best within a certain range of environmental conditions that mimic their native habitat. If
your plant is native to a dry climate, it might prefer lower water potential levels. Conversely, plants from wetter environments might tolerate
higher water potentials.
3. **Observe Plant Behavior**: Watch your plants closely for signs of stress related to water. Wilting, leaf curling, yellowing, and stunted growth
can indicate both overwatering and underwatering. Adjust watering practices based on these observations.
4. **Soil Moisture Testing**: Use a soil moisture meter to regularly check the moisture level in the soil. This can give you a practical indication
of whether your plant is receiving too much or too little water.
5. **Consult Experts**: Local gardening clubs, nurseries, or agricultural extension services often provide advice tailored to your region’s
climate and soil conditions. They can offer insights into the specific water needs of plants commonly grown in your area.
6. **Experiment and Adjust**: Initially, it might require some trial and error to find the optimal watering routine for your plants. Start with
general guidelines based on your research and adjust based on how your plants respond.
7. **Understand Water Potential**: Water potential is a more technical measure that involves factors like soil type, salinity, and atmospheric
conditions affecting the plant's ability to take up water. While it's important for agricultural and research purposes, everyday gardeners
typically focus more on observing plant behavior and adjusting watering accordingly.
By combining these approaches, you can develop a good sense of the appropriate water potential range for your plants. Remember, consistency
and observation are key to maintaining healthy plant growth and ensuring they receive the right amount of water.
Identifying Ideal WP Ranges
Chat GPT response

14. Different plant species have different ideal
water potential ranges
•Drought tolerance
•Stress induced ideal traits/quality
Dr. Sterling Taylor, one of the founders of
Environmental Biophysics, published ideal
ranges for a wide range of crops
Sterling Taylor 1918-1967
Image:dlsciencesocieties.org
Identifying Ideal WP Ranges
How do I know the optimal range for different plants?
Taylor, Sterling A. and Gaylen L. Ashcroft. Physical Edaphology. The
Physics of Irrigated and Nonirrigatedsoils. 1972
L.J. Aronson, A.J. Gold, and R.J. Hull. 1987. Cool-Season Turfgrass
Response to Drought Stress. Crop Science. 27:1261 –1266

15. Identifying Ideal
WP Ranges

16. When it comes to choosing water potential sensors,
there are many options out there
Water Potential Sensors
How to choose the right sensor for your application

17. What is best for my research?
What is your application?
•Measuring water fluxes
•Plant stress
•Slope stability
What is your soil/media?
•Expected water potential
ranges
Maintenance needs?
•Site accessibility

18. Typical Water Potential Ranges:
-30 to -100 kPa
User needs:
Low maintenance
Sensors fully buried
Ideal sensor:
Calibrated solid matrix sensor
Applications
Turf irrigation

19. Typical Water Potential Ranges:
+100 to -80 kPa
User needs:
Positive pore pressure measurements
Accuracy near saturation
Ideal sensor:
Tensiometers typically
Solid matrix sensor in some cases
Applications
Slope stability

20. How can installation impact the
accuracy of my measurements?

21. •Most sensors measure temperature
along with other parameters
•How does our installation impact the
accuracy of those temperature
measurements?
•Experimented with 4 different cable
routings
Improving Temperature Measurements
Cable routing impacts

22. Improving Temperature Measurements

23. Water potential data has many applications
beyond knowing how available water is to plants
•Generating soil moisture release curves
•Measuring water fluxes
Resources in existing literature for identifying
ideal water potential ranges
Know the needs of your application when
identifying which water potential sensor to use
Conclusion

24. Questions
Leo Rivera, MS
Director of Scientific Outreach
METER Group, Inc.
2365 NE Hopkins Ct, Pullman, WA USA 99163
T: [phone]
E: [email protected]
W:www.metergroup.com