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ARS Home » Plains Area » Lubbock, Texas » Cropping Systems Research Laboratory » Plant Stress and Germplasm Development Research » Research » Publications at this Location » Publication #144581
Title: LABORATORY EVALUATION OF A COMMERCIAL DIELECTRIC SOIL MOISTURE SENSOR

Author
item McMichael, Bobbie
item LASCANO, ROBERT - TEXAS A&M UNIV

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2003
Publication Date: 11/1/2003
Citation: McMichael, B.L., Lascano, R.J. 2003. Laboratory evaluation of a commercial dielectric soil moisture sensor. Vadose Zone Journal. 2(3): 650-654.

Interpretive Summary: The measurement of changes in the water content of the soil is critical for the development of management strategies for efficient water utilization by crop plants. Many currently used methods do not provide the needed information on a timely basis or are very expensive for large-scale cropping systems. A study was conducted to evaluate, under laboratory conditions, the utility of a relatively low cost commericially available sensor that could potentially be used in a large field cropping system situation. The results of the laboratory tests revealed that the output of the sensors was sensitive to changes in temperature in the range of 60 to 100 degrees fahrenheit. The results also indicated that the sensors became relatively insensitive to changes in soil water content at the higher water content levels (20-25 percent water content by volume). Both of these situations could be experienced routinely in a growing season. Given these limitations, the sensors would have limited application for measuring changes in soil water content in an agricultural cropping system.

Technical Abstract: Development of management strategies for efficient water utilization of crop production requires measurements of changes in soil water content on a dynamic basis. Many of the methods currently used for measuring these changes are destructive, not timely, or relatively expensive for large-scale investigations. A commercially available low cost, non-destructive soil moisture sensor for measuring changes in soil volumetric water content (VWC) based on changes in the dielectric constant of the soil-water was evaluated under laboratory conditions across a wide range of temperatures and water contents. Probes were placed in containers filled with de-ionized water and soil (Amarillo fine sandy loam). The containers were placed in a programmable temperature chamber and subjected to a series of changes in both temperature and VWC. Results indicated that the output of the probes between air-dry and a VWC of 25 percent for the soil used was not linear at a constant temperature. When the soil temperature varied between 15.9 C and 39.1 C at a constant VWC, probe output changed the equivalent of 10 percent by volume. The temperature sensitivity was 0.5 mV/C for air-dry soil and about 5 mV/C for wet soil. Given their non-linear response to increasing water content and sensitivity to temperature limit their application to measure soil water.