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New Polymer Tensiometers: Measuring Matric Pressures Down to the Wilting Point

^a ALTERRA, Wageningen Univ. and Research Centre, Droevendaalsesteeg 4, 6708 PB, Wageningen, the Netherlands
^b Dep. of Environmental Sciences, Soil Physics, Ecohydrology and Groundwater Management Group, Wageningen Univ. and Research Centre, Droevendaalsesteeg 4, 6708 PB, Wageningen, the Netherlands
^c Lab. for Physical Chemistry and Colloid Science, Wageningen Univ. and Research Centre, Dreijenplein 6, 6703 HB, Wageningen, the Netherlands
^d Faculty of Science and Technology, Twente Univ., Langezijds LA 1727, P.O. Box 217, 7500 AE, Enschede, the Netherlands

View larger version (16K): [in this window] [in a new window]   Fig. 1. Polymer tensiometer with disk-shaped ceramic containing an -Al2O3 support layer (1), a -Al2O3 membrane (2), a stainless steel cup (3), a polymer chamber (4), a pressure transducer (5), and a synthetic ring (6). Different polymer chamber volumes were obtained by adjusting the length of the stainless steel cup between the two arrows.

View larger version (17K): [in this window] [in a new window]   Fig. 2. Overview of the various experiments with six polymer tensiometers (POTs, Table 2), involving temperature effects (2, 4), drying and rewetting (5), performance in soil material (6), and long-term stability (1, 4).

View larger version (12K): [in this window] [in a new window]   Fig. 3. Initial pressure peaks and long-term pressure drops for polymer tensiometers (POTs) 1, 5, and 6 (Table 2) when placed in water.

View larger version (13K): [in this window] [in a new window]   Fig. 4. Initial pressure peaks and long-term pressure drops for polymer tensiometers (POTs) 2, 3, and 4 (Table 2) when placed in water.

View larger version (12K): [in this window] [in a new window]   Fig. 5. Pressure response of polymer tensiometer (POT) 3 (Table 2) to abrupt temperature changes using a water bath.

View larger version (7K): [in this window] [in a new window]   Fig. 6. Scaled pressure (P)–temperature (T) relationships for the polymer tensiometers (POTs, Table 2) when placed in water.

View larger version (15K): [in this window] [in a new window]   Fig. 7. Pressure response of polymer tensiometer (POT) 3 (Table 2; placed in water) to a sinus temperature wave.

View larger version (14K): [in this window] [in a new window]   Fig. 8. Self-restoring capacity of polymer tensiometer (POT) 3 (Table 2). The tensiometer was temporarily removed from the water reservoir between Days 58 and 61.

View larger version (15K): [in this window] [in a new window]   Fig. 9. Matric pressures recorded by different instruments placed in soil. Day 0 in the figure corresponds with Day 202 in Fig. 2. Table 2 lists key features of polymer tensiometer (POT) 4.