Soil physical experimental research is hampered by the very limited measurement range of water-filled tensiometers. With a newly developed polymer tensiometer (POT) it is possible to measure matric potentials over a range of 0 to -2.0 MPa; this corresponds to a matric head of 0 to -200 m. The POT consists of a solid porous ceramic in contact with the soil, which encloses a chamber containing a polymer solution rather than water. The objective of our study was to investigate the performance of POTs in laboratory settings for both wet and dry soil. Polymer tensiometers, conventional tensiometers and TDRs were placed in the evaporation container that was filled with repacked sand (1% clay, 2% silt and 97% sand). Initially the soil was wetted uniformly, then left to dry out, and when soil matric potentials dropped below -2.0 MPa the soil was wetted uniformly again. Soil samples were taken to calibrate TDR measurements and relate TDR data to the pF-curve. Results show the polymer tensiometers are able to measure soil water potentials in both wet and dry soils, have fast response times to changing water potentials, and need calibration for temperature variations.

This research is funded by the Dutch Technology Foundation (STW). Contributing companies are: ECO Ceramics BV (www.ecoceramics.nl), ENRIN (www.enrin.nl) and KELLER Meettechniek BV (www.keller-holland.nl)