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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 Cliff, Your post is interesting. Can you give approximate proportions of the sand and silt to mix? What is the citation for this result? By the way, I don't necessarily disagree with your recommendation. Some potting mixes don't work at all well with TDR, others do. Thanks for your help. Steve At 08:16 PM 4/12/2000 +0000, you wrote: > >Reply to Jason Murray, > >I would NOT recommend TDR in that environment. The TDR only works when there >is a continuous water film. Isolated water does not register. > >Try a simple experiment. Get a course grained material (eg diat. earth or a >sand) and mix it with a pure silt. The idea is to get two distinct pore >sizes. Add water to field capacity approx. then dry and test with TDR. You >will find that when the sand dries, the TDR no longer registers the water in >the silt. this phenomena is documented in the literature. > >I suspect this situation will happen frequently in the sort of materials you >describe. > >I see no reason why tensiometers would not work . > >Cliff.hignett@soilwater.com.au > >owner-sowacs@aqua.ccwr.ac.za wrote: > >> I am conducting a study examining variability issues associated with using >> Time Domain Reflectometry to monitor moisture and thus control irrigation >> in horticultural substrates. I am using pine bark mix, hardwood bark >> mix, pro-mix, perlite, sand, and rockwool. I am looking for (and have >> yet had a hard time finding) data on the variability associated with using >> tensiometers to monitor moisture in these same/similar substrates. I am >> looking to find whether TDR is a less variable source of moisture data for >> irrigation scheduling than tensiometers. So, actual tensiometer >> variability data is what I really need. >> >> Thank you for the help, >> either email me direct at jmurray@wam.umd.edu, >> or reply to the list. >> Much appreciated, >> Jason Murray > >-- >Cliff Hignett >Soil Water Solutions >45a Ormond Ave >Daw Park >South Australia 5041 >pH 61 (08) 8276 7706 >WWW.SOILWATER.COM.AU > > ___________________ 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/