Belyaeva O1, Ward G1, Chen D1, Suter H1.
1 University of Melbourne, Vet and Agri Science, Bld. 184, 30 Flemington Road, Parkville, Victoria, 3052, https://www.unimelb.edu.au, firstname.lastname@example.org
Knowledge of soil moisture is needed to understand crop water use and improve water-use efficiency: capacitance probes can be used for this. However, often generic calibrations supplied by the manufacturer the probes are used and this can lead to errors. The aim of this study was to estimate the accuracy of using generic calibration relationships for capacitance probes to monitor soil water. A set of 4 probes (0-120 cm depth) were installed at irrigated and non-irrigated pasture sites and calibrated using the traditional core-sampling technique. For the sandy top soil (up to 30 cm), the factory generic calibration overestimated soil moisture with a significant error of 0.05-0.28 m3/m3. For deeper clay horizons the error between the generic calibration and actual moisture tended to be larger. This increased error in sub-soils can be associated with changing bulk density and porosity down a profile and, on this soil, also presence of voids and cracks. Using the generic calibration would lead to a significant overestimation of volumetric soil water at the high water content (>0.45 m3/m3) and understating at the dry end (<0.17 m3/m3). The findings show that a soil specific calibration of the capacitance probes is required for accurate soil moisture measurements.