Campbell Scientific Sentek EasyAG Installation Guide v 3.0 User Manual

Page 15

Site Selection

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, probes should be installed 50 to 100 metres away from the head ditch. Probes
should not be installed 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 probes here may be considered when
measurement of deep percolation below an irrigated field is required. Consideration should also be given to
placing another probe 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 probes to monitor the site. Place one probe under the tree canopy 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 two probes 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 probes 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).

Disclaimer:

Sentek is not responsible for incorrect or poor selection of site locations. The data

recorded by the probes is only accurate for the soil immediately surrounding the

probe. How that information is extrapolated to reflect what is happening over a

larger area is dependent upon the location of the probe and whether or not it is

representative. Sentek can not be held responsible for the impact of management

decisions made for a larger area based on data recorded from a probe.