Water content determination in saline soils using self-contained tdr and electrical capacitance systems

摘要

Encapsulated time domain reflectometry (TDR) and electrical capacitance soil moisture measurement systems can be used in a variety of irrigation management applications. These self-contained systems are relatively inexpensive, easily automated, andmeasure over a wide range of volumetric soil water contents. However, soil moisture readings are often unreliable in highly saline soils and information on the effects of salinity on the sensor output is limited. Soil moisture measurements of four commercial devices, including a TDR cable tester (Trase), two encapsulated TDRs (Aqua-Tel and Trime), and one encapsulated capacitance sensor (Theta), were obtained over a wide range of water contents and salinity levels during laboratory studies with a sand medium. All four systems were affected by salinity and performed poorly at or near saturated conditions. The Trase produced a sufficient amount of reliable soil moisture data, which was used as a standard to evaluate the other sensors. The Aqua-Tel and Theta units did not lose sensitivity to soil moisture as the salinity increased, but the output was shifted upwards significantly. The Trime became less sensitive to salinity as it increased, while the output also shifted upward. In order to produce soil moisture values that are independent of soil conditions, all of the encapsulated systems need a method to correct the reading for soil salinity.