Water Potential Data: Best Practices for Lab & Field Measurements
How to get the most out of your water potential data—Best practices for field and lab. Are you leaving critical insights buried in your soil data? Soil moisture content tells you how much water is present. But soil water potential—also called soil suction—predicts how that water will move and how available it is to plants. Water potential is the key to understanding drought stress, infiltration, water availability, and crop response. And yet, it’s one of the most underused and misunderstood measurements in agriculture and environmental science, partly because traditionally, it has been a difficult measurement to collect and interpret. Choosing the wrong sensor, improper installation, and an incomplete measurement range can all compromise the accuracy of your data, leading to incorrect inferences and decisions. In this 30-minute webinar, METER Research Scientist Leo Rivera will break down the complexities and show you how to get the most accurate, useful water potential data—in both field and lab settings. You’ll learn how to: - Choose the right sensor for your specific research or operational goals - Avoid common pitfalls in field installation that compromise accuracy - Capture the full soil moisture release curve using multiple lab instruments - Integrate data from lab and field for better modeling and deeper insight - Pair water content with water potential to reveal what your plants actually experience - And more Whether you’re managing irrigation or modeling the vadose zone, this session will help you capture cleaner data, make stronger decisions, and avoid costly misinterpretations.
Water Potential Data: Best Practices for Lab & Field Measurements
- 2. HOW TO GET THE MOST OUT OF YOUR WATER POTENTIAL DATA Best practices for field and lab measurements Leo Rivera METER Group, Inc
- 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 VS. INTENSIVE Properties Extensive • Volume • Water Content • Heat Content Intensive • Density • Water Potential • Temperature
- 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. ψT = ψm + ψg + ψo + ψp • ψT – Total water potential • ψm – matric potential - adsorption to surfaces • ψg – gravitational potential - position • ψo – osmotic potential - solutes • ψp – pressure potential - hydrostatic or pneumatic TOTAL WATER POTENTIAL Sum of components
- 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 this improve our understanding of hydraulic properties? APPLICATIONS OF WATER POTENTIAL DATA How can we best utilize this measurement?
- 7. MEASUREMENT METHODS Field & Lab
- 8. Field sensors measure matric potential Indirect measurements • Heat dissipation • Capacitance Direct measurements • Tensiometers • High capacity tensiometers MEASURING WATER POTENTIAL Field measurements Indirect Methods Direct Methods
- 10. • Standard matrix equilibrates with soil • Water content of matrix is measured through capacitance of heat dissipation technique • Sensors calibrated to output water potential based on ceramic characteristics FIELD SENSORS Capacitance & Heat dissipation
- 11. FIELD SENSORS Solid matrix sensor pros & cons Advantages • No maintenance required • Large sensing range • Covers plant available range • Good accuracy for calibrated sensors Disadvantages • Accuracy dependent on calibration • Limited wet end performance (0 to -10 kPa) • Temp sensitivity on very dry end
- 12. • Equilibrates water under tension with soil water through a porous cup • Pressure sensor directly measures suction of water FIELD SENSORS Tensiometers
- 13. Advances in sensor capabilities • Digital pressure transducers • Minimize water column • External refilling • Measures + and - pore pressures • Extended measuring range* FIELD SENSORS Tensiometers Ceramic Cup Digital Pressure Transducer External Refilling Tubes
- 14. FIELD SENSORS Liquid equilibration pros & cons Advantages • Highest accuracy of any sensor in wet range • Positive pore pressure measurements Disadvantages • Limited to water potential from 0 to -90 kPa • Significant maintenance requirements
- 15. Laboratory instruments used for generating Soil Moisture Release Curves Can also be used for single point measurements Typical Measurement Techniques • Evaporation method • Pressure plates • Chilled-mirror dewpoint MEASURING WATER POTENTIAL Laboratory measurements
- 16. • Starts with a saturated soil core • Tensiometers measure water potential and gradient during evaporation • Gives both moisture release curve and unsaturated hydraulic conductivity function EVAPORATION METHOD HYPROP
- 17. • Sealed chamber with sample reaches vapor and temperature equilibrium • Measures sample and mirror temperature • Optical sensor detects the presence of dew formation on a mirror that is chilled with a Peltier cooler • Very wide range: 1 to 3000 bars (0.1 to 300 MPa) CHILLED-MIRROR DEWPOINT TECHNIQUE WP4C
- 19. MEASUREMENT BEST PRACTICES Field deployment & installation
- 20. Proper sensor installation is critical! • Install into undisturbed soil • Good sensor-to-soil contact • Minimize site disturbance Common installation methods • Trench wall • 10 cm diameter auger hole: side wall installation • Augered holes for direct insertion SENSOR INSTALLATION Keys for good measurements
- 21. SENSOR INSTALLATION Advances:TEROS Borehole Installation Tool
- 22. Borehole installation method • 10 cm auger hole (minimal disturbance) • Perfectly linear insertion • Extendable to >10 m depths SENSOR INSTALLATION Advances
- 23. Augered installation method • 16 mm (5/8 in) augered hole • Installation at different angles • Sensor can be removed SENSOR INSTALLATION Advances
- 24. MEASUREMENT BEST PRACTICES Getting the most out of laboratory measurements
- 25. SOIL MOISTURE RELEASE CURVES Measuring the full range HYPROP WP4C
- 26. BEST PRACTICES Full characterization Accounting for hysteresis • Wetting vs drying curves Evaporation method (drying curve) Vapor pressure methods (wetting & drying) Sampling from HYPROP sample
- 27. BEST PRACTICES Subsampling from HYPROP Subsample from both ends of core Sample from inner sections of sample
- 28. BEST PRACTICES Full characterization Matric (ψm) vs. Osmotic potential (ψo) • Tensiometer methods measure ψm • Vapor pressure methods measure ψm+ ψo Correct of ψo with saturated extract EC
- 29. MEASUREMENT BEST PRACTICES Laboratory vs field measurements
- 30. BEST PRACTICES Understanding limitations Field measurements: Complete soil interaction Lab measurements: Single-point assessment
- 31. Sensors:Water potential/water content (2 depths: 7 & 15 cm) SOIL MOISTURE RELEASE CURVES Field measurements
- 32. SOIL MOISTURE RELEASE CURVES Field measurements
- 33. 7 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 (15 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) SOIL MOISTURE RELEASE CURVES
- 34. Key to availability of water to plants & optimizing crop yields Water potential is one of the primary drivers of water and solute movement in soils CONCLUSIONS Water potential is the key
- 35. QUESTIONS Leo Rivera, MS Director of Scientific Outreach METER Group,Inc. 2365 NE Hopkins Ct, Pullman, WA USA 99163 T: +1 509 332 2756 E: leo.rivera@metergroup.com W: www.metergroup.com