Evaluation of Commercially Available Electromagnetic Sensors for Measuring Soil Water Content and Electrical Conductivity In Mineral, Organic and Saline Soils.

An increasing number of electromagnetic sensors (EM) are deployed to measure soil water content and electrical conductivity for hydrological characterization and ecosystem studies and for agricultural purposes such as irrigation scheduling, yet little is known about effects of mineral composition, organic matter and elevated salt concentrations on sensor response. Ten well characterized source soils spanning the entire textural range were utilized to thoroughly test the influence of clay and organic matter content, iron oxides, ferromagnetic minerals and salinity on water content and EC measurements. Tested sensors included the Campbell CS616, the Acclima TDT, Hydra, Theta, SM300, 5TE, 10HS and TDR probes, which are based on different measurement principles ranging from Time Domain Reflectometry and Time Domain Transmission to capacitance and impedance technology each with a different oscillation frequency. Soil samples were brought to different water content while maintaining a constant bulk density. The influence of the soil texture, organic matter and electrical conductivity were evaluated for each sensor and the validity of factory supplied-calibration relationships were tested.