Umwelt-Geräte-Technik GmbH
| Eberswalder Str. 58 | D-15374 Müncheberg | phone: +49 (0) 33 43 2 - 89 575 |
2.2.
What are Tensiometers used for?
The tension corresponds to the force which a plant has to apply via the roots to extract water from the
soil pores. Among other applications, tensiometers can be used for irrigation. The difference between
the tensions at two points within the soil acts as the driving force for soil water transport. Determining
this gradient by using tensiometers enables the evaluation of water movement in the soil regarding flow
direction and velocity. Tensiometer measurements are essential for the comprehensive analysis of the
water balance of a region or an ecosystem.
2.3.
How Does a Tensiometer Work?
The operating principle of the Full Range Tensiometer differs slightly from water filled tensiometers.
Both kinds of tensiometers consist of an air-tight sealed, medium-filled measurement chamber, a unit
where the pressure transducer is located, and a porous cup, usually made out of ceramic. The pores of
the ceramic cup are filled with water and connect the liquid of the measurement chamber inside the
tensiometer with the water in the soil outside the tensiometer. By connecting the two liquid bodies the
pressure conditions inside the tensiometer are always adjusted to the pressure conditions of the water
in the surrounding soil. If the soil dries, water will flow through the pores of the porous tensiometer cup
from the measurement chamber into the soil. In case of water filled tensiometers the measurement
volume is filled with water. Water that leaves the measurement volume via the pores of the ceramic
creates a negative pressure inside the tensiometer. If the surrounding soil is wetted again, for example
by a precipitation event or irrigation, the negative pressure decreases in the surrounding soil and water
flows from the soil into the measurement volume, whereby the negative pressure in the measurement
volume is reduced again.
In case of the Full Range Tensiometer the measurement volume is filled with water that is bonded to a
polymer.
figure 3 Schematic representation of the functional principle of a Full Range Tensiometer
