SWT4 User Manual v3.1
Installation
15
3 Installation
3.1 Advance planning
3.1.1 Selecting the measuring site
The installation spot should be representative of the soil horizon!
Therefore, in heterogeneous soils, soil samples should be taken and
classified before or during installation.
On farmed sites with vegetation, root spreading and root growth during
the measuring period must be considered. Fine roots will grow around
the Tensiometer cup as this is a poor but still secure source of water.
Therefore, avoid the root zone or move the Tensiometer from time to
time depending on the root growth.
Disturbing effects like the edge of a field, slopes or hollows must be
avoided or taken into account when interpreting the data.
3.1.2 Number of Tensiometers per level
The deeper the level, the less the variation is in water potential. In
lower sandy or pebbly horizons just one Tensiometer per depth is
sufficient. Close to the surface about 3 Tensiometers per level are
recommended.
Guiding principle: More heterogeneous sites and soil structures
require a higher number of Tensiometers.
3.1.3 Extent of the site
A large number of well-spaced samples will help reduce sampling
errors in heterogeneous soils.
To obtain a differential description of the soil water situation, at least 2
Tensiometers are recommended per horizon, one in the upper and one
in the lower level.
The maximum recommended cable length for SWT4 and SWT4R is 40
meters.
Accuracy: long cables reduce the accuracy.
Lightning: cables act as antennas and should always be as short as
possible.
