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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 Jac, I would be very leary of this setup. Depending on the frequency of wetting events (rain or irrigation) the clay annulus could be very much out of phase with the sand for important lengths of time. It surprises me that the tubes would be installed in this manner. Installing the Diviner 2000 access tubes directly in sand should be very easy as long as one does not auger too far ahead of the tube (can cause a cavity to form if sand collapses into the auger hole). Steve At 12:53 AM 5/27/2000 +0000, you wrote: >I recently acquired a Diviner2000 moisture probe. The supplier installs the >access tubes by drilling a hole of 10mm bigger OD, inserts the PVC tube and >settles it in with a clay mixture (similar to potters clay - the exact >compostion I am not sure of), to ensure perfect contact between tube and >soil. > >We work with sand (as in sand dunes) with moisture holding capacity as low >as 45 mm/m. > >I am wondering what the effect of the clay band in direct contact with the >tube could be. >Can I assume that the sand-clay will reach equilibrium, in a short enough >time to give me the correct response. > >Your comments will be appreciated. > >Thank you: Jac le Roux >jac@besproeiing.co.za > > > > > ___________________ Steve Evett, Soil Scientist USDA-ARS, 2300 Experiment Staton Rd., Bushland, TX 79012 USA 806-356-5775, FAX: 806-356-5750 srevett@ag.gov, http://www.cprl.ars.usda.gov/programs/