Using a CWS655, when should a soil-specific calibration be performed?

To get accurate water content readings, a soil-specific calibration is probably required if any of the following are true:

  • The soil has more than 5% organic matter content.
  • The soil has more than 20% clay content.
  • The soil is derived from volcanic parent material.
  • The soil has porosity greater than 0.5.

For details on performing a soil-specific calibration, refer to “The Water Content Reflectometer Method for Measuring Volumetric Water Content” section in the CS650/CS655 manual.

Some users have obtained good results by applying a linear correction to the square root of reported permittivity before applying the Topp et al. (1980) equation. The linear correction is obtained by taking readings in saturated and dry soil and using volumetric water content measurements obtained from oven-dried soil samples to estimate actual permittivity. 

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