Campbell Scientific Sentek EnviroSCAN Access Tube Installation Guide - Manual (Page 14)

Sit e Selection
© Sent ek Pt y Lt d Page 11
In the example illustrated below, cans in the blue shaded area received above average water; those in the
red shading below average; while those in the green shaded area received an average amount.
Due to the specific nature of each site in terms of irrigation system, it is inappropriate to give prescriptive
advice on tube placement. For soil moisture monitoring, tube placement should however, be representative
and consistent of the area being watered. General guidelines for commonly used systems and principles of
sample site selection follow.
For sprinkler systems, it is preferable to use two access tubes per site, placing one into an area receiving
average precipitation and the other one into a wet or dry spot, depending on a soil salinity or water table
problem.
In centre pivots, if the distribution uniformity tests show significant variation between booms, two or more
access tubes should be installed, with at least one tube in each different area. For high pressure rain guns,
measure the water application pattern under different wind conditions to ensure that you don’t pick on area of
extremely low or high water application.
Installation of probes in drip irrigated crops needs consideration of the extent of the ‘wetting onion.’ Use at
least two probes to monitor soil moisture of drip irrigated crops to measure both the vertical and the lateral
spread of water. The schematic below shows an example of the variation in the wetting pattern below a
dripper. The darker blue colour signifies wetter soil conditions, while the lighter blue colour signifies drier soil
conditions. The plant roots will utilize the water from different locations under the dripper at different
intervals; therefore it is very important to measure these differences using more than one probe.