Campbell Scientific Sentek TriSCAN® Manual v 1.2a - Manual (Page 32)

TriSCAN Manual Version 1.2a
Copyright © 1991 – 2004 Sentek Pty Ltd All rights reserved Page 25
Micro scale zone selection
During macro zone selection you identified the irrigation management units on your property. Micro scale
zone selection targets the actual site of the access tube in relation to crop and irrigation delivery point.
Note:
Micro zone selection is equally as important as macro zone selection and has a direct effect on the
representative value of the data.
In soil-based monitoring, the measurements are taken from a small part of the root zone. Sentek sensors
record the dynamics of moisture in the part of the soil profile where the access tube has been installed. If
you miss the root system or install the access tube in abnormally dry or wet irrigation spots, the data will not
be representative of the irrigation management unit.
Micro zone selection guidelines
The following is a set of guidelines for selecting access tube installation sites within irrigation management
units. Two major factors need to be taken into account; irrigation and plant health.
Irrigation system
It is important to check that your irrigation system is performing as per design specifications prior to
installation and at least annually thereafter. Variations in sprinkler pressure and flow, pump performance,
distribution uniformity and wind can result in uneven patterns of watering. This can lead to; the development
of water tables, dry spots and salinity problems.
Conducting a Distribution Uniformity (DU) test
Prior to installation, it is also necessary to check the distribution uniformity (DU) of the system. This can be
done with a simple can test. The method involves arranging cans in a grid pattern, in a representative area
within the macro zone. In the example illustrated in Figure 5, cans in the blue shaded area received above
average water; those in the red shading below average; while those in the green shading, received an
average amount.
Figure 5. Example Water DU test results
A DU of salinity at the proposed probe site can act as a valuable check to ensure that an especially saline or
non-saline site has been chosen. Samples should be collected in a grid, at the same depths as the probe
sensors. A simple 1:5 EC test for each sample will provide an EC DU. As before excessively high or low
unrepresentative areas should be avoided. Areas such as fertilizer preparation or turn-around zones should
be avoided.
Figure 6 below illustrates the degree of salinity uniformity found in a potato field. It can be seen that,
although the salinity distribution uniformity is high at each depth, it is possible to inappropriately site a probe
in a position of high salt by mistake. It also shows the degree of inherent difference in ECe at depth. Greater