• HYPROP soil moisture release curves from METER Group (formally UMS)

• Unsaturated soil hydraulic conductivity on undistrubed soil samples

• High resolution and accuracy in the 0 to -100 kPa range

• Rapid determination of soil hydraulic properties

automated soil moisture release curves

Soil moisture release curves, or soil water characteristic curves (SWCC), are critical measurements for soil scientists and engineers. Traditional methods are labourious, often taking weeks to months to complete a full curve. The HYPROP 2 advances measurements of SWCC as it is automated and relatively rapid (one to two days). As a bonus, the HYPROP 2 can also measure soil hydraulic conductivity on undisturbed soil samples.

The HYPROP 2 is ideal for measurements in the wet range of soils (0 to -100 kPa range). When used in combination with the WP4C Dewpoint Poteniameter, a complete SWCC from fully wet to air dry soils (-300 MPa) can be completed.

further details

HYPROP 2 is a fully automated measuring and evaluation system based on Schindlers evaporation method (1980) to determine the hydraulic properties of soil samples.

With tensiometers in two depths the device measures the soil water tension as well as the unsaturated hydraulic conductivity. Additional the volumetric water content is calculated through a continuous recording of weight loss. With these information the water retention curve can be illustrated.

HYPROP (HYdraulic PROPerty analyser) is a device to measure hydraulic key functions of soil samples in a comfortable and reliable way by using an evaporation experiment.

Wind (1966) developed the evaporation method in the mid-sixties. For this 5 tensiometers were put in a soil sample. The sample was set on a balance and over the evaporation process the tensions and the mass change of the sample were measured in time intervals. Based on these data the water retention function and the unsaturated hydraulic conductivity in the range between saturation and maximum 500 hPa (50 kPa) were calculated by means of an
iteration process.

Schindler (1980) simplified this method. He used only 2 tensiometers and simplified the evaluation procedure. HYPROP is working based on this method. The method was tested several times and its fitness for use was proven by scientific analysis (Wendroth et al., 1993, Peters and Durner, 2008; Peters et al., 2015). New research results yielded a further simplified measuring procedure (Schindler and Mueller, 2006) and an extended measuring range (Schindler et al., 2010a and Schindler et al., 2010b). Using the HYPROP one can today measure simultaneously the water retention curve and the unsaturated hydraulic conductivity function in the range between water saturation and close to the permanent wilting point. The measuring time amounts – depending on the soil – from 2 days (clay samples) to maximum 10 days (peat and sand samples). Additionally the dry bulk density of the sample is determined.

multi-mode measurements

The measurement and evaluation can be run in two modes. In the multi balance mode (one balance per sample) the lab employees’ work effort is limited to set up and take away the samples. In the single balance mode (one balance for more samples) up to 20 samples can be measured in parallel. In this mode it is necessary to put the probes manually on the balance twice a day. This takes about 15 s per sample and weighing. The measurement of the tension runs automatically. The software HYPROP-VIEW enables a comfortable data logging and storage. The software HYPROP-FIT provides the same comfort for data evaluation, fitting and export of the hydraulic key functions.

The hysteresis of the saturation and dewatering characteristics of the hydraulic key functions is described in Schindler et al. (2015).

Measurements considering the shrinkage characteristics of the soil sample are described in Schindler et al., 2015. Comparing the measuring results of HYPROP and classical methods (sand box, kaolin box, pressure pot) demonstrated good congruence (Schelle et al., 2010, 2011, 2013a, b; Schindler et al., 2012). Systematical differences could not be found.

For more details on measurement theory, please consult the HYPROP 2 manual.