Eight commercially available electro-magnetc water content sensors were evaluated in seven well-characterized soils ranging from sand to clay textures, including an organic soil. Factory supplied calibrations were compared and sensor response to soil properties demonstrated. Soil-specific calibrations yielded measurement accuracies from 0.015 to 0.025. An increasing number of electromagnetc (EM) sensors are deployed to measure volumetric soil water content (q) for agricultural, ecological, and geotechnical applications. While impedance and capacitance sensors generally operate at frequencies between 20-300 MHz, time domain-refectometry (TDR) and-transmissometry (TDT) function in the GHz range. In general, lower frequency sensors are less expensive but more sensitive to confounding effects of salinity, temperature, and soil textural variations. To simplify sensor application, factory-supplied calibrations are often provided for different porous media types such as mineral, organic, and saline soils, or soilless-substrates. The objective of the presented study was to evaluate the performance of eight commercially available EM moisture sensing systems (TDR 100, CS616, Theta Probe, Hydra Probe, SM300, Wet2, 5TE, 10HS) in seven well-characterized and texturally varying soils using a standardized approach. The validity of factory supplied-calibraton relatonships was evaluated and the influence of soil properties on the EM responses for q measurements was observed. Results indicate that the factory-supplied calibraton relatonships for groups of mineral and organic soils in general performed well, but some inconsistences were identified and suggestions for improvement are discussed. Soil-specific calibrations from this study yielded accuracies of around 0.015 m3m-3 for 10HS, SM300, and Theta Probe, while lower accuracies of about 0.025 m3 m-3 were found for TDR100, CS616, Wet2, 5TE, and the Hydra Probe. These results are based on mineral soils having a large variaton in texture, electrical conductvites below 2 dS m-1, organic mater below 10%, and specific surface areas of less than 50 m2 g-1.
ASJC Scopus subject areas
- Soil Science