With an increasing amount of soil moisture monitoring sensors on offer in the market today there is growing importance on not only having sensors installed but actually understanding the information they provide. This blog is written to give some insight into the data they you might receive from one of these devices. The following traces are the output of an AquaCheck soil
moisture sensor with 3G telemetry. The sensors measure soil moisture and temperature every 30 minutes. The data is available to Agri Optics clients from the AquaCheckWeb platform. For more info see our website http://www.agrioptics.co.nz/portfolio/aquacheck/
The key to getting the most out of your soil moisture sensor
is to have an accurate field capacity (FC) and refill point for the probe site
calculated. The most convenient way of identifying Field Capacity is to have
the probe installed prior to the winter period. Typically there will be enough
precipitation to allow the profile to recharge to FC. FC can also be identified
by saturating the profile manually with a large quantity of water. The key points we are looking for when identifying FC is a
repeated filling to saturation then drainage of the profile. The point where drainage ceases
can be identified as FC. Night time events are more accurate as ET is not a
factor.
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| Fig 1. Identifying field capacity |
The next key feature to identify is drainage.
Drainage is classified as the loss of soil water past the effective rooting
zone. The effective rooting zone varies dependent on the crop. Once the depth
of plant roots has been identified we can identify any drainage. For the graph
below if the crop has a rooting depth of 600mm. The bottom pink line represents
the sensor at 600mm. We can see the lift and subsequent drainage of soil water
past the effective rooting zone of 600mm.
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| Fig 2. Drainage events |
The third key piece of information that the AquaCheck package
provides is the ability to set variable management allowable deficit (MAD)
lines. These lines create the target “Green Zone” typically between 85% and 15%
of readily available water (RAW). Using MAD lines leaves room for any rain so
that any free rain water is not wasted as drainage. It also gives an indication
when soil moisture is approaching stress point. The MAD is able to be adjusted to
give a desired target soil moisture zone for crop and pasture growth stages e.g. establishment or harvest.
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| Fig 3. MAD Lines |
The final bit of information that becomes available once the
crop starts growing is the daily soil water usage. The staircase like moisture trace is showing us evapotranspiration and it allows us to see the impact that increasing crop biomass and
increasing temperatures are having on crop or pasture water usage. Crop rooting
depth can be identified by seeing how far down the water usage is occurring. In fig 2. above below the roots are drawing moisture down to 600mm vs a later spring sown
wheat in fig 4. which is only drawing water to 400. Note the size of
the usages. This relates to the root mass at the given depths.
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| Fig 4. Crop water usage |
I hope these tips are useful when interpreting your soil
moisture data and that it results in more efficient scheduling of your
irrigation this summer. Irrigation New Zealand also has some more tips and info
on their website http://irrigationnz.co.nz/news-resources/irrigation-resources/
Post By Nick