Response of a new soil water sensor to variable soil, water content, and temperature

The success of time domain reflectometry (TDR) has led to the development of other instruments that use the soil dielectric constant as the basis for determining volumetric soil water content. An example is the Water Content Reflectometer (WCR; Campbell Scientific, Logan, UT), which is much less expensive than TDR and is used widely, although little has been published concerning its applicability to soil water Content monitoring.(I) The primary objectives of this study were to determine the WCR soil water calibration for different soils and to investigate how it is affected by changing temperature. We found the individual sensors to be very precise (alpha less than or equal to 0.05) under the controlled laboratory conditions of this study, Variability among sensors, determined in air and ethanol, indicated significant (alpha = 0.05) sensor differences that were largely accounted for with a simple additive Correction. Sensor soil water calibration was investigated in four soils under varying water contents across a 40 degreesC temperature range. We found that (i) soil water calibration was significantly (alpha = 0.05) different for each soil tested, (ii) there was a significant (alpha = 0.05) temperature response for all soils, and (iii) the effect of temperature varied with soil water content and soil type. Both the soil type and temperature sensitivities rye observed were probably due to the relatively high electrical conductivity (EC) of the soils tested.