|Parkin, Gary - UNIVERSITY OF GUELPH|
Submitted to: Vadose Zone Journal
Publication Type: Review Article
Publication Acceptance Date: August 30, 2006
Publication Date: November 16, 2005
Citation: Evett, S.R., Parkin, G.W. 2005. Advances in soil water content sensing: The continuing maturation of technology and theory. Vadose Zone Journal. 4:986-991. Interpretive Summary: As the introduction to a special issue of Vadose Zone Journal, this paper reviews the state of the art in soil water content determination. Many of the new sensors discussed respond to electromagnetic properties of the soil that vary with water content. The discussion centers on calibrations of the sensors and interferences that may prevent them from operating correctly. Chief among these is soil electrical conductivity, which increases with fertilization and sometimes with irrigation, and which can be a problem in areas having salty soils. The review explains how scientific research has clearly identified the problems with these sensors, leading to the opportunity to design a new generation of sensors that can operate correctly in problem soils that are important to production agriculture.
Technical Abstract: Since the work of Topp et al. in 1980, establishing a theoretical and practical basis for soil water content determination by time domain reflectometry (TDR), and the work of Dean and Bell in 1987 on a resonant capacitance technique for soil water determination, there has been a plethora of related sensors and sensing systems introduced commercially. These sensors respond to electromagnetic (EM) properties of soil and may be termed jointly EM sensors. However, they differ widely in several important characteristics including susceptibility to interferences, precision, accuracy, and volume sensed. Most of the papers presented in this special issue of Vadose Zone Journal attempt to define the characteristics of EM soil water content sensors, calibrate them in various soils and in response to various interfering factors, and evaluate sensors in terms of their ability to respond to changes in the soil bulk dielectric permittivity. And, a few papers explore other soil properties that are relevant to water content or potential determination. The challenges to scientists are made clear. The next generation of soil water sensors must address interferences due to soil bulk electrical conductivity and interacting factors, and they must sense volumes large enough to encompass the representative elemental volume for soil water content in most soils. We thank the authors for responding to the call for papers. The resulting group of papers well advances the maturation of technology and theory of soil water content sensing.