Measuring water potentials is important for the optimization of the water application scheme in irrigated agriculture. Existing methods for measuring water potentials directly in both wet and dry soils are complicated, expensive, inaccurate or not suitable for use in field situations. A newly developed polymer tensiometer (POT) makes it possible to measure soil water potentials especially in dry soils and can be used in wet soils as well. With the polymer tensiometer it is possible to measure soil water potentials over a range of 0 to -2.0 MPa; corresponding 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 small chamber containing a polymer solution rather than water. The polymer is retained by a micro-porous filter on the side of the ceramic that encloses the chamber containing the liquid. A pressure transducer records the pressure of the osmotic polymer solution. A major advantage of the POT is the fact that the measured pressure is directly related to the matric potential. The range over which the POT can measure covers the range of soil water potential values over which plants are able to take up water. Direct observation of the potential of soil water at different locations in the root-system will yield knowledge about the ability of a plant to take up the water in situations with water and salinity stress. Current research focuses on the improvement of a prototype polymer tensiometer, its performance in different types of soils, and the observation of the potential of soil water at different locations in the root-system.

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)