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Soil Water Characteristic Curves (SWCC) / Moisture Release Curves

Characterization of soils according to their moisture holding capacities and moisture flow retention characteristics is essential for the development of an effective irrigation and plant stress management system for growing commercial food crops.
Soil scientists know that having soil water retention curves can save them thousands of dollars over the lifetime of a farm.

Analog options

Sandbox for pF-determination

The standard set for pF-determination pF 0 - 2.0 (0 - 0.1 bar) consists of the sandbox with control panel, suction levelling stand, water supply bottle with stand, filter cloth (140-150 micron), a number of containers synthetic sand, grain size approximately 73 micron and various accessories. A maximum of 40 soil sample rings can be placed on the sandbox. The samples that are measured are taken using soil sample rings. These rings usually have a contents of 100 cc. In addition to the standard set a soil sample ring kit must be available as well as cases with soil sample rings and aluminum soil sample boxes
The standard set for pF-determinations pF 2.0 - 2.7 (0.1 - 1 bar) consists of a sand/kaolin box with control panel, an electronic suction level control system (pressure range 0 - 600 hPa) with integrated control panel, pressure sensor and 10 l tank, containers with synthetic sand, a container with kaolin clay and various accessories. For the determination of the complete pF-range (0 - 2.7) the sand box and the sand/kaolin box can be applied in one single setup next to each other

The Pressure Plate Apparatus is suitable for determination of pF-curves in the range pF 2.0 - 4.2 (0.1 - 15 bar of suction). Futhermore the sets are suitable for the calibration of soil moisture blocks or soil moisture measurement equipment. This system provides the most complete range of extractors for determining water holding capacities (water retention curves) of soils and porous materials. The 1600 extractor provides pressure plate processing of low soil suction values (0-5Bars), the 1500 provide "plate" extraction methods up to 15 bars, and the 1000 provides the specialized processing required on shrink / swell clays and materials with low contact capabilities. The 0700LAB123 simply provides the most complete professional extraction system available. A system covering all aspects of soil water retention studies.

Digital Options

HYPROP

HYPROP is a modular lab instrument that generates a moisture characteristic curve and determines the unsaturated hydraulic conductivity of soil samples in standard 250 ml soil sampling rings. After setup, the system generates the moisture characteristic while running unattended.
Two precision mini-tensiometers measure water potential at different levels within the sample while the sample rests on a precision laboratory scale (2000 gram range; 0.01 gram resolution). As the sample dries, changes in water potential are correlated to changes in moisture content using the Wind/Schindler evaporation method.
Results are verified and values for dry range and saturation are calculated according to a selected model (i.e., van Genuchten/Mualem, Bimodal van Genuchten/Mualem, or Brooks and Corey.) Model parameters can be selected before, during, or after the measurement procedure. Learn more Learn more

 

WP4C

The WP4C measures water potential by determining the relative humidity of the air above a sample in a closed chamber. Once the sample comes into equilibrium with the vapor in the WP4C's sealed chamber, the instrument finds relative humidity using the chilled mirror method.
This method entails chilling a tiny mirror in the chamber until dew just starts to form on it. At the dewpoint, the WP4C measures both mirror and sample temperature with 0.001°C accuracy. This allows the WP4C to deliver water potential readings with unparalleled accuracy in the -0.1 MPa to -300 MPa range.
The WP4C can be used to measure the water potential of any porous material. It's typically used to analyze soil, soilless substrates, plant material, and seeds, but it has been used to measure a variety of unusual things, including apples, bricks, oil, and insect carapaces. Learn more

VAPOR SORPTION ANALYZER

The Vapor Sorption Analyzer (VSA) brings click-and-read efficiency to soil water characteristic curves (SWCC). In 24 to 48 hours, the VSA generates curves with 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

Guide to Water Potential Units

FC: Field Capacity – a typical value for the drained upper limit of water potential in soil

PWP: Permanent Wilting Point – a typical value for the lower limit of plant available water in soil