METER TEROS 21 - Measuring in High Salinity; Temperature Sensitivity

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SYSTEM
estimated by measuring the soil temperature accurately (Koopmans and Miller, 1966). For
each 1 °C decrease in temperature below 0 °C, the water potential in the soil decreases by
~1,200 kPa. Spaans and Baker (1996) showed that this relationship is valid in field soils for
water potentials below about −50 kPa.
Rigorous testing indicates that repeated freeze–thaw cycles do not affect the ceramic discs.
Several sensors were equilibrated in saturated soil and then subjected to numerous freeze–
thaw cycles in a temperature-controlled chamber. The freezing rate of the soil containers
was at least an order of magnitude faster than could be achieved in field soils under natural
conditions. At several points during the test, and at the end of the test, the ceramic discs
were evaluated for damage due to repeated rapid freezing of pore spaces full of water. None
of the ceramic discs showed any signs of physical damage, and none of the sensors showed
any significant change in output due to the freeze–thaw tests.
3.4.2 MEASURING IN HIGH SALINITY
A saturation extract electrical conductivity (EC) greater than 10 dS/m will confound the
capacitance measurement taken by the sensor resulting in erroneous matric potential
readings. It is recommend that the TEROS 21 only be used in environments where the
saturation extract EC does not exceed 10 dS/m.
3.4.3 TEMPERATURE SENSITIVITY
Fluctuations in temperature can affect the capacitance readings at matric potential less
than about −500 kPa (Figure7). Although temperature can affect the output of the reading,
the nature of the moisture retention curve of the ceramic results in an extremely small effect
on matric potential until the substrate dries out to about −500 kPa. A small change in water
content can result in a relatively large change in matric potential beyond −500 kPa.
−1,800.0
−1,600.0
−1,400.0
−1,200.0
−1,000.0
−800.0
−600.0
−400.0
−200.0
0.0
010203040506070
WATER POTENTIAL (kPa)
Sensor 1 (5-cm depth)
Sensor 2 (15-cm depth)
TIME (DAYS)
 Temperature sensitivity data for TEROS 21 sensors