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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Soil, Water & Air Resources Research » Research » Publications at this Location » Publication #207398

Title: Use of Soil Moisture Sensors in Problem Soils

item Logsdon, Sally

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/21/2007
Publication Date: 3/21/2007
Citation: Logsdon, S.D. 2007. Use of Soil Moisture Sensors in Problem Soils [abstract]. Logsdon, S.D. 2007. Activation energies and temperature effects from electrical spectra of soil [abstract]. Conference Proceeding Hawaii Soil Moisture Sensing Technology Conference: Current and Future Research Directions in Soil Mosture Sensing. p. 22.

Interpretive Summary:

Technical Abstract: Soil dielectric sensors are based on the assumption that all soil water has the permittivity of free water (~76 to 80 depending on temperature and salt load) at all relevent frequencies (< 1.5 GHz); however, this assumption is not valid when there are appreciable amounts of water sorbed to high charge clays or organic matter. The purpose of this review is show where this assumption is in error, and what the consequences are for soil moisture sensing. Soils containing high-charged clays usually have high measured electrical conductivity that is not due to salinity. The charges develop in the water sorbed to the clays. The high electrical conductivity gives these soils a positive temperature response for the apparent permttivity because of the incorporation of the imaginary component that includes electrical conductivity. Sensors based on the real permittivity have less temperature sensitivity for these soils. The high charge clays attenuate the electrical signal, resulting in a small sampling volume. This small volume is even smaller for coated probes or for sensors that are placed inside a plastic access tube. In spite of these limitations, successful measurements can be made with some soil dielectric probes on these soils, using site-specific calibration.