Density-dependent calibration of multisensor capacitance probes in coarse soil

Coarse-textured reconstructed soils are utilized extensively in the reclamation of mining waste. Accurate and continuous sensing of soil water content is required to understand soil water dynamics and evaluate the hydraulic characteristics of these soils. The EnviroSCAN (Sentek Pty. Ltd, Australia) is a semi-permanent multisensor capacitance probe (MCP) capable of continuous measurement of volumetric water content (theta(v)) and has been used to monitor reclamation soil cover performance. Calibration of these probes is required to improve the accuracy of field measurements. In this study, field and laboratory measurements were undertaken over a range of water contents and bulk densities to refine the relationship between theta(v) and scaled frequency (SF) measured by the MCP. The manufacturer's calibration equation tended to underestimate theta(v) under wet conditions (theta(v) > 0.35 cm(3) cm(-3)). Our experimental data showed that bulk density (rho(b)) did affect the MCP calibration and consequently a new calibration equation that includes the effect of rb is developed using laboratory measurements and validated using field measurements. This equation provided the highest degree of correlation and the smallest standard deviation of prediction to measured values of theta(v) for laboratory and field measurements, respectively. This calibration improves the application of the EnviroSCAN for coarse-textured soils such as those utilized in this study.