Soil Solution Electrical Conductivity Measurements Using Different Dielectric Techniques
- Yasser Hamed,
- Magnus Persson * and
- Ronny Berndtsson
Accurate measurements of soil solution electrical conductivity (σw) are needed in various applications. One recently developed technique that measures σw is the Sigma Probe (SP). The SP is supposed to give accurate readings only slightly dependent on water content (θ) and soil type. To test the performance of the SP, it was compared with another dielectric technique, time domain reflectometry (TDR). Both techniques utilize the dielectric constant (K a) and bulk electrical conductivity (σa) to estimate the σw Measurements of σw were obtained in a laboratory experiment using nine different soil types with θ in the range 0.05 to 0.50 m3 m−3 In each soil type, three different σw were used (approximately 0.3, 1.2, and 3.0 dS m−1). The linear σw–σa–θ model used by the SP contains only one soil specific parameter (K 0). Using this model, the SP readings were constant over the encountered range in θ, whereas the TDR estimation calculated by the same model typically increased at K a values below the range of 10 to 15. Using the SP with a default K 0 value of 4.1 typically gave a σw that was ±20% of the true σw when σw > 1 dS m−1 The error in the σw estimation for σw lower than 1 dS m−1 can be much larger except in sandy soils. The TDR measurements of σw using a conventional σw–σa–θ model were more accurate in all soil types at all θ, with root mean square errors that were lower by about 50% compared with the SP readings. However, this model requires soil specific parameters that have to be obtained during a calibration experiment.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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