Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2003
Publication Date: 5/20/2004
Citation: Kelleners, T.J., Soppe, R.W., Ayars, J.E., Skaggs, T.H. 2004. Calibration of capacitance probe sensors in a saline silty clay soil. Soil Science Society of America Journal. 68:770-778.
Interpretive Summary: Soil water content is an important parameter in many agricultural and environmental studies. Measuring soil water content by electromagnetic techniques has become very popular because it is rapid, safe, non-destructive, and easily automated. There is concern, however, about the influence of soil salinity on the instrument readings. We developed a calibration procedure for measuring soil water content with a commercially available electromagnetic sensor. The procedure was tested on a saline silty clay soil in California's San Joaquin Valley. Measured and predicted soil water contents compared reasonably well, although predicted water content was overestimated by about 15 percent at high water content. The calibration procedure will benefit the wide range of people who are interested in monitoring soil water content, including farmers, water managers, government agencies, and researchers.
Technical Abstract: Capacitance probe sensors are a popular electromagnetic method of measuring soil water content. However, there is concern about the influence of soil salinity on the sensor readings. In this study capacitance sensors are calibrated for a saline silty clay soil. The calibration procedure incorporates both the observed response of the sensors in the saline soil and the theoretical response of the sensors in non-lossy soil (no energy losses due to ionic conductivity or relaxation). The difference between the sensor frequency in non-lossy soil and saline soil as a function of ionic conductivity was described with S-shaped curves (r2 of 0.82 and 0.34 at two locations). Volumetric water content was calculated by correcting for the reduction in frequency that occurs when the sensor is used in saline soil. Measured and predicted volumetric water contents compared reasonably well (r2 = 0.86), although predicted volumetric water content was overestimated by about 15 percent at high water content.