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well i have been a tdr user and fan for quite some time and am glad to hear all this good sense talk about keeping things simple and using the good old topp equation. After all, not having to calibrate for specific soil type is what makes tdr such a nifty technique. In my experience, working with difficult desert soils, there is generally more error in the bulk density measurement needed to convert gravimetric water content to volumetric water content, than there was in the tdr measurement to begin with! Steve e. also brings up a very good point about the interpretation of the tdr trace which is usually not mentioned in great detail and can make quite a significant difference in the measured water content. The only soils where i have found specific calibration necessary has been in conductive soils where tdr over predicts water content. In such soils the problem is futher complicated because the tdr traces become more difficult to interpret due to signal attenuation. Sam hokett desert research inst. las vegas, nv