INFLUENCE OF IRON MINERALS ON THE DETERMINATION OF SOIL-WATER CONTENTUSING DIELECTRIC TECHNIQUES

Measurement of soil moisture content based on changes in dielectric co nstant has become a standard approach in recent years. Time domain ref lectrometry (TDR), in particular, has gained rapid acceptance as a tec hnique for measuring soil moisture that can be used in a wide range of applications. The capacitance soil moisture probe has been demonstrat ed also to have a large number of potential uses. One factor that diel ectric soil moisture determining techniques have in common is the need for calibration. The capacitance probe needs to be calibrated for eac h soil type, and recent research has shown that it is advisable for th e same strategy to be adopted with time domain reflectometers. Results presented show the influence that iron minerals such as magnetite, ha ematite and goethite can have on the calibration of time domain reflec tometers and capacitance probes. Magnetite shows the greatest effect b y causing an uncertainty of up to 60% in the estimation of volumetric water content in the presence of 15% magnetite.