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NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs Dr. Sun, I am a little surprised at your response since we discussed our problems with your firm a couple of years ago. We were interest in the moisture profile down to 1 meter and installed a dozen Moisture Point type "K" multiple segment probes. In our soils with 50% clays, the 1 meter probes were unable to provide physically feasible, much less accurate measurements below the first segment. Volumetric water content readings greater than one were common! The high DC conductivity of the soil attenuated the input pulse such that the signal processing algorithm was unable to detect the return signal. We talked to your firm and exchanged data files; all to no avail. We pulled the 1 meter probes and exchanged them with 60 cm probes. Same problem. Those probes have been pulled and now sit in the corner of my office to remind me not to throw away my neutron probes. I have no complaints about the service provided by your firm. You responded promptly and I believe in good faith. Sometimes stuff happens and we all learn. However, a review of your web site would indicate that your multiple segment probes will work in high conductivity soils. That seems curious. I suggest your repeat your experiment with your 142.5 cm "A" type probe and see what happens. glenn brown -----Original Message----- From: owner-sowacs@aqua.ccwr.ac.za <owner-sowacs@aqua.ccwr.ac.za> To: gbrown@ceat.okstate.edu <gbrown@ceat.okstate.edu> Date: Sunday, April 16, 2000 3:50 PM Subject: Moisture.Point in heavy clay >NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za >with the body of the message containing the line: >unsubscribe sowacs > >Dear Dr. Glenn Brown > >I have just finished a test of measuring volumetric water content of heavy >clay content using TDR (Moisture.Point MP-917). The clay I used is Rideau >Clay with no less than 60% of clay content. The electrical conductivity >(Ec)of the solution (1:5 soil/water ratio) is approximately 0.10-0.14 dS/m. >The probe used is ESI's "C" type probe, 30 cm in length with shorting diode >at both ends of the probe. Moisture.Point's patented shorting diode >technology provides a reliable relationship between time delay and >volumetric water content. When the soil moisture was below 0.35m3/m3, the >displayed moisture reading was lower than the actual one because of the >effect of bound water (due to its low dielectric constant). When the >moisture increased to more than 0.35 m3/m3 then the effect of bound water >can be neglected. Moisture.Point provided correct moisture readings up to >0.60 m3/m3. > >If you are working in heavy clay with a high moisture range, Moisture.Point >can be used without special calibration. However, if you are working in a >low moisture range, then the theoretical linear relationship between time >delay (express as T/Tair) and volumetric water content must be adjusted >since the linear relationship doesn't account for the bound water effect. > >In moderate saline heavy clay situations, something interesting happened. >High Ec causes signal attenuation, resulting in over-estimation of water >content, and which partially and beneficially compensates for the bound >water effect in a low moisture range. However, it leads to an >over-estimation when soil moisture is high. A special calibration may solve >this problem. I would be more than happy to discuss my experiment and the >application of TDR in heavy clay with my colleagues. > >Jason Sun Ph.D. > >Research Scientist >ESI Environmental Sensors Inc. >100-4243 Glanford Avenue >Victoria, BC, Canada >V8Z 4B9 >Tel: 250-479-6588 >Fax: 250-479-1412 >e-mail: jason@esica.com