The potential for error when measuring water potential
Measuring soil water potential is never easy. Traditional methods such as pressure plates or filter paper have always been problematic. Not only are they extremely time consuming, but both methods have issues with accuracy. That’s why we developed the WP4C.
Simply accurate. Simply fast. Simple to use.
As world experts in water potential and soil suction, it wasn’t enough to engineer an instrument that delivered consistent accuracy. We also designed it to be easy to use and take only minutes to register measurements, even in dry soils. The WP4C is a complex instrument due to its versatility, but extremely easy to use with sample sizes up to 7 ml. Simply fill half of the cup with soil, leaves or seeds, and then equilibrate the sample.
Proven first-principles method based on fundamental physics
The WP4C is so accurate, it’s used to calibrate other measurement methods and has been published extensively. Why? The dew point sensor inside the WP4C is a primary measure of water potential, not some secondary parameter merely correlated with water potential. It measures the combined matric and osmotic potential using fundamental thermodynamics and a finely-tuned calibration. Here’s how it works:
The WP4C determines the relative humidity of the air above a sample in a sealed chamber (conforms to ASTM D6836). Once the sample comes into equilibrium with the vapor, relative humidity is determined using the chilled mirror method. This involves chilling a tiny mirror until dew starts to form. At the dew point, the WP4C measures both mirror and sample temperature within 0.001 °C. This allows for unparalleled accuracy in the -0.1 MPa to -300 MPa range so you can have full confidence in sample readings.
Only using partial curves? Get what you’ve been missing.
Now, generate full, high-resolution moisture release curves across the entire moisture range by combining WP4C data with HYPROP data. No other method generates a curve with this much detail, or with this little effort.
If you only need the dry end of the curve, the HYPROP FIT Software can be used to plug in water potential data collected by the WP4C for fitting different water retention models (i.e., van Genuchten, van Genuchten Bimodal, Fredlund & Xing, Brooks & Corey).
Save time and effort
The design of the WP4C is incredibly efficient in a number of ways. To start, you don’t have to spend a ton of time teaching your technicians. Plus, it allows for fast equilibration because of sophisticated temperature control. And a final feature that makes for a total time saver: it makes measurements on its own, so you’re free to attend to other things.
World-class soil water potential measurement
Unparalleled accuracy. Simplicity of use. Fast speeds. Combine the WP4C with other LABROS instruments for a complete soil analysis. Add the PARIO for soil particle size analysis, and use data from the HYPROP and the KSAT to generate a hydraulic conductivity curve.
Range: 0 to –300 MPa
Range 15-40 °C
Length 24.1 cm (9.5 in)
Powder painted aluminum
|Sample cup capacity|
15 mL (0.5 oz) full
3.2 kg (7.1 lb)
20 x 2 alphanumeric LCD with backlighting
Chilled-mirror dew point sensor
Minimum 5 °C
Standard RS-232 to USB cable (included)
Manufactured under ISO 9001:2015
California requires the following notice:
⚠️ WARNING: This product may contain chemicals including ethylene glycol, lead, nickel, styrene and cadmium, which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov
LEARN MORE WITH ARTICLES, CASE STUDIES, DEMOS, WEBINARS
- Cited publications WP4C
- The researcher’s complete guide to water potential
- Lab vs. field instruments: Why you should use both
- Soil moisture release curves: Why you need them. How to use them.
- How to create a full moisture release curve using the WP4C and HYPROP
- Webinar: Soil moisture 201: Moisture release curves—revealed
- Webinar: Water potential 201: Choosing the right instrument
- Case study: Does early planting increase risk to winter canola?
- Case study: Irrigation curves—A novel irrigation scheduling technique
- SEE ALL WP4C KNOWLEDGE BASE ARTICLES
- SEE ALL WP4C WEBINARS
Have a question or problem? Our support team can help.
We manufacture, test, calibrate, and repair every instrument in-house. Our scientists and technicians use the instruments every day in our product testing lab. No matter what your question is, we have someone who can help you answer it.
Phone Europe: +49 89 12 66 52 0