Water potential describes the force that drives water movement. It is the most fundamental and essential measurement in soil physics.
Unfortunately, it's also a tricky thing to measure. The chart on the right (click on it to view the full image) shows range and accuracy for available instruments and sensors. You can find more information about each instrument's advantages and limitations on the individual product pages. For more information on water potential theory, see the resources list on the right.

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Generate detailed moisture release curves on undisturbed soil samples in a standard 250 ml sample ring, typically within a few days. Range: 0 to -85 kPa. Hyprop also determines unsaturated hydraulic conductivity values for the soil sample. » Learn more
The Vapor Sorption Analyzer (VSA) brings click and read efficiency to soil moisture release characteristic curves. In 24 to 48 hours, the VSA generates up to 200 data points (water potential vs. water content) for both adsorption and desorption. The VSA works in the dry (-10 to -475 MPa) range. You can create automated soil-water characteristic curves and generate all the correlations with clay activity, surface area, and swelling potential. With the new static feature, you can hold humidity constant and look at the way soil takes up water into its crystal structure (2:1 clays) and monitor water content change over time. » Learn more
Fast, Accurate Water Potential Measurements Use the WP4C to measure water potential in 5 to 10 minutes. Range: -0.1 to -300 MPa* wp4C video Versatile The WP4C can be used to measure the water potential of any porous material. It's typically used to analyze soil, soilless substrate, plant… » Learn more