Campbell Scientific Sentek EnviroSCAN Access Tube Installation Guide - Manual (Page 15)

Sit e Selection
© Sent ek Pt y Lt d Page 12
In addition, in drip irrigation, the slope needs to be taken into consideration, to account for movement of
water down slope.
In furrow irrigated fields, access tubes should be installed 50 to 100 metres away from the head ditch.
Access tubes should not be installed solely at the opposite side to the head ditch, as tail water from the
irrigation may back up the furrows and give unrepresentative readings. Placement of tubes here may be
considered when measurement of deep percolation below an irrigation field is required. Consideration
should also be given to placing another tube in the middle of the field to measure the depth of irrigation
there.
Plant health
Select a site next to an average-sized, healthy plant representing the Irrigation management unit. Avoid:
• Stunted or sick plants
• Unusually large plants or trees
• Spots where plants are missing
General guidelines for key crops include:
• In field crop and vegetable production, choose a uniform crop stand, and ensure that the
probes are inserted within the actively growing root zone.
• In orchards, use two access tubes to monitor the site. Place one access tube under the
canopy of the trees and another outside the canopy – there will be some interception of rainfall
by the canopy so less rain water will penetrate the ground directly under the canopy. Select a
site that represents dynamic data trends (more root activity) and again consider irrigation
distribution uniformity.
Soil properties
Soil properties influence probe placement in drip irrigation, as the wetting pattern is highly dependent upon
the soil. In uniform sands, most of the water applied under the dripper will tend to move vertically through
the profile, with minimal lateral spread. Conversely, in uniform clay soils, the water will tend to spread
laterally as well as vertically. In soils of contrasting textures, there will be varying wetting patterns that need
to be taken into consideration.
In many soils there are substantial variations in the thickness of horizons and in the potential rooting depth.
This can lead to significant variations in soil water storage capacity and plant growth over relatively short
distances. Under these conditions, it is recommended to install to two access tubes to ensure that this
variability is taken into account.
Other micro zone selection considerations
There are several other factors when considering micro zone selection that also need to be taken into
consideration. These are:
• Do not install access tubes in outside rows. These locations are usually exposed to wind and
dust, particularly in the vicinity of roads or adjoining broad-acre properties.
• Avoid the ‘drip ring’ in, for example, citrus orchards, where sprinkler irrigation water is
channeled by the canopy to the outside bottom edge of the foliage creating wetter soil
conditions at the edge of the canopy.
• Avoid wheel tracks (and wheel track rows) as the soil is more compacted in these areas and
stores less readily available water than the rest of the field (non wheel track rows).