Monday, November 13, 2006 - 10:55 AM

Polymer Tensiometers and Root Water Uptake under Water-Stressed Conditions.

Martine Van Der Ploeg1, Harm Gooren1, Rene Hoogendam1, Gerben Bakker1, Cindy Huiskes2, Luuk Koopal1, Henk Kruidhof2, and Ger de Rooij1. (1) Wageningen University, Nieuwe Kanaal 11, Wageningen, 6709 PA, Netherlands, (2) Twente University, Faculty of Science and Technology, Enschede, Netherlands

Root water uptake is driven by the difference between the potential of the soil water and the root water. In field situations, this cannot be measured adequately in the dry range. Conventional tensiometers (CT) are limited to -0.085 MPa or -8.5 m, while root water uptake is possible until at least -1.5 MPa or -150 m. Pressures can be measured indirectly with Time Domain Reflectometry (TDR), but TDR is not accurate in dry soils. Direct measurement will provide a tool to optimize irrigation gifts in water-scarce environments and benefits soil physical and production ecology research. We developed a polymer tensiometer (POT) that is able to measure down to -2.0 MPa or -200 m. 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 soil water pressure than the pure water in a conventional tensiometer. We investigated root water uptake strategies under water-stressed conditions. We used 3 lysimeters of l´w´h=0.70´0.50´1.50m. We installed 3 instrumental layers with TDR, POT and CT at 0.2, 0.6 and 1.1 m depth. Three irrigation intensities were applied to create no (matric head (hm) between -2.0 and -14 m), mild (minimum hm­: -45 m) and severe (minimum hm: -80m) water stress in the period with plant growth.This research is funded by the Dutch Technology Foundation (STW). Contributing companies are:
ECO Ceramics BV(, ENRIN ( and
KELLER Meettechniek BV(