HR: 1340h
AN: H53G-1508    [Abstracts]
TI: Measurement of soil water potential over an extended range by polymer tensiometers: comparison with other instruments
AU: * van der Ploeg, M J
EM: martine.vanderploeg@wur.nl
AF: Wageningen University, Environmental Sciences, PO Box 47, Wageningen, 6700 AA, Netherlands
AU: Gooren, H P
AF: Wageningen University, Environmental Sciences, PO Box 47, Wageningen, 6700 AA, Netherlands
AU: Hoogendam, R C
AF: Wageningen University, Laboratory for Physical Chemistry and Colloid Sciences, PO Box 8038, Wageningen, 6700 EK, Netherlands
AU: Bakker, G
AF: Alterra, PO Box 47, Wageningen, 6700 AA, Netherlands
AU: Huiskes, C
AF: 4University of Twente, Faculty of Science and Technology, Inorganic Materials Science, PO Box 217, Enschede, 7500 AE, Netherlands
AU: Koopal, L K
AF: Wageningen University, Laboratory for Physical Chemistry and Colloid Sciences, PO Box 8038, Wageningen, 6700 EK, Netherlands
AU: Kruidhof, H
AF: 4University of Twente, Faculty of Science and Technology, Inorganic Materials Science, PO Box 217, Enschede, 7500 AE, Netherlands
AU: de Rooij, G H
AF: Wageningen University, Environmental Sciences, PO Box 47, Wageningen, 6700 AA, Netherlands
AB: In water scarce areas, plant growth and productivity can be severely hampered by irregular precipitation and overall water shortage. Root water uptake is mainly driven by matric potential gradients, but measurement of soil water matric potential is limited by the measurement range of water-filled tensiometers (-0.085 MPa). Other measurement techniques indirectly measure soil water potential by converting soil water content with the use of the water retention curve. In dry soils, the water content measurements may become insensitive to small variations, and consequently this conversion may lead to large errors. We developed a polymer tensiometer (POT) that is able to measure matric potentials down to -2.0 MPa. The POT consists of a solid ceramic, a stainless steel cup and a pressure transducer. The ceramic consist of a support layer and a membrane with 2 nm pore-size to prevent polymer leakage. Between the ceramic membrane and the pressure transducer a tiny chamber is located, which contains the polymer solution. The polymer's osmotic potential strongly reduces the total water potential inside the polymer tensiometer, which causes build-up of osmotic pressure. Hence, the water in the polymer tensiometer will cavitate at a much lower matric potential than the nearly pure water in a conventional tensiometer. 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 under conditions of water shortage or salinity stress. With this knowledge it will be possible to adjust existing unsaturated flow models accounting for root water uptake. We tested 8 POTs in an experimental setup, where we compared matric potential measurements to TDR water content measurements, matric potentials derived from measured water contents, and matric potentials measured by water-filled tensiometers. The experimental setup consisted of two evaporation boxes, one filled with sand (97.6% sand, 1.6% silt, 0.8% clay), and the other with loam (42.8% sand, 38.8% silt, 18.4% clay). The uniformly repacked soils were saturated at the beginning of the experiment, then drained, and left to dry out. Results show that polymer tensiometer data are comparable to the other instruments in their measurement ranges, and highlight the risks of converting water contents to matric potentials. 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).
DE: 1866 Soil moisture
DE: 1875 Vadose zone
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting