CALIBRATION OF CS615 AND TDR INSTRUMENTS FOR MARHURANGI, TARRAWARRA AND POINT NEPEAN SOILS

Campbell Scientific CS615 instruments for soil moisture measurement have been installed in surface and sub-soils at 18 locations at one field site in New Zealand and at 7 locations at two field sites in Australia. Spatial patterns of soil moisture have also been collected at each of these sites on several occasions, using a Time Domain Reflectometer (TDR). Each type of instrument was calibrated after field sampling and after a review of the literature indicated that it might be necessary. Calibration for temperature and soil moisture effects was carried out in the laboratory using repacked soils. Satisfactory temperature calibrations were achieved for both instruments, but for the TDR it made little material change to the soil moisture estimates. Satisfactory soil moisture calibrations were also achieved for the TDR for each soil. There was a good relationship between soil moisture contents of the repacked soils measured by both instruments. However, the relationship between field CS615 measurements and those taken close-by using TDR showed a consistent departure that was greatest at high soil moisture levels. The TDR measurements were consistent with soil samples from the field assessed using the gravimetric method. Possible reasons for the departure are advanced.

Maurice J Duncan
NIWA
Christchurch, New Zealand

Andrew W Western, Christopher Olszak, Julian Thompson, Tom Anderson, Rodger B. Grayson, David Wilson and Rodger Young
University of Melbourne
Victoria, Australia.