Campbell Scientific EnviroSCAN Sentek Water Content Profile Probe - Manual (Page 31)

Appendix C. Access Tube Installation
The information below is a summary. Further information is provided in the
Sentek Diviner2000
® Installation Guide Version 1.0, available as a .PDF file
from Campbell Scientific, Inc.
Sensors must be installed correctly into the soil medium. The soil around the
sensor needs to be representative of the rest of the field.
The aim of the installation is to cause minimum disturbance to the crop and soil
profile. Disturbances to the soil may produce pockets of air or loosely packed
soil material. These conditions will cause preferential flow of irrigation water
or rain to a greater depth compared with the rest of the field. Access tubes
must be installed to fit tightly in the soil along their entire length.
Permanent errors can be introduced into the measurements through poor or
hasty installations. Air gaps existing between the sensors (or access tubes) and
the soil will bias sensor readings, i.e. the sensor will read high when the air
gaps are filled with water and low when they drain. Poor installation is a
primary source of inconsistencies between sensors.
The additional time taken in careful installation ensures access to accurate and
meaningful data. Sentek has developed precision installation tools to be used
for the installation of Sentek access tubes. The precision of the access tubes
and tools is designed to complement the high value of the readings taken by the
Sentek sensors.
Sentek access tube installation tool kits are not designed
to withstand the stresses often required by installations in
dry clays. While the tools should withstand the installation
of a few tubes, expect tool failure, resulting replacement
costs, and occasional distorted and unusable access
tubes. CAUTION
Access tubes are to be installed at monitoring sites chosen using a series of
proven evaluation methods. Monitoring sites must be selected so that
information gathered from them is representative of surrounding crop / ground
cover water use and soil water capacity. Appendix D discusses site selection.
Always try the standard manual installation method first. Alternatively, a
slurry method is available for installations in soils with high stone and gravel
content. However, the slurry method may have an impact on soil moisture
readings at those sites.
To identify the tools required to install access tubes, examine the soil profile
with a shovel or backhoe at the proposed monitoring sites.
An access tube is required for obtaining air readings in the probe
normalization procedure. Campbell Scientific recommends that
you perform the normalization procedure as described in
Appendix B prior to installing all available access tubes. NOTE
C-1