Dielectrically Relaxing and Electrically Conducting Suspensions for Testing Water Content Sensors

There are countless soil moisture sensors in use around the world, yet little information is available to users regarding sensor performance under various environmental conditions. We suggest here a standard for assessment of electromagnetic (EM) soil moisture sensors using dielectrically relaxing and lossy (electrically conductive) materials. These two properties represent the most challenging conditions found in, for example, heavy clay soils (vertisols), which can exhibit both dielectric relaxation at the measurement frequency and electrical conductivity (EC), characteristics which both vary with temperature. Users would benefit from evaluation and understanding of sensor performance under such conditions, especially when comparisons among sensors are available. We present a laboratory method using a silica flour suspension in glycerol as a reproducible test standard, to which salts may be added to include effects of ionic conductivity.