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Soil moisture monitoring in Southland

By Dianne Elliotte

Senior Environmental Technical Officer

Soil moisture and temperature monitoring began in 2002 with two sites in Northern Southland as part of a groundwater recharge investigation project.  We now have 18 sites throughout the province. 

The ES network expanded in 2006, providing a tool for farmers to guide them with the management of farm dairy effluent.  In addition to effluent irrigation, the soil moisture data is used in a range of other projects including catchment runoff and flood warning modelling, providing more precise assessments of groundwater recharge, water use and allocation efficiency.

The soil moisture network is a well utilised resource by farmers – not only dairy farmers but pasture irrigators using the information to monitor when is the best time to apply effluent or start irrigating paddocks so it is utilised by the plant at optimum soil moisture and temperature conditions.

Our soil moisture tapes are currently checked biennially but this may change with the new national environmental monitoring standards (NEMS) where core samples may need to be obtained and analysed in a lab for volumetric soil moisture percentage.

We have had a few issues setting up the network in regards to installation depth of the Aquaflex tapes and the process itself.  This has been highlighted with the differences in soil moisture values with the installation of two tapes at each site as part of our replacement schedule.

With these differences in soil moisture readings from the two tapes, questions arise around the difference in installation depths. Does putting the tapes in 50mm deeper create this much difference? Was more care needed when installing these tapes during the early stages of the network expansion (as a protocol was only developed in 2008/2009)?  Does installing the tapes outside the enclosure allowing stock access provide a more realistic representative environment for measuring soil moisture?

Many farmers use the information available on the website about the soil moisture conditions and soil temperatures – we know this as when there are any website issues we get calls from the public, so it is paramount that our network is representative of the conditions at least at a district scale. 

In summary the ES soil moisture network has grown rapidly without many concrete standards in place until recently.