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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 Tom, The short answer is that you cannot be sure that the Diviner 2000 and the Watermarks are responding to soil water in the same manner. In fact, you can be fairly sure that they do not. After all, one measures a surrogate of volumetric water content (soil apparent permittivity) and the other measures a surrogate of soil water potential. To relate between the two you would need to establish a curve of soil water content vs. potential. Even then, hysteresis would bolux up the works - the curve changes depending on whether the soil is wetting or drying. In some soils the difference between curves is large, in others it's not so important. But, Bruce's suggestion would give you a quick way to evaluate the correspondence. Steve At 06:59 PM 4/3/2000 +0000, you wrote: >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 > >I have done some moisture monitoring with Watermarks in the past and now >have use of a Diviner 2000 from Sentek. I wish to be able to compare >previous years data to current data. One problem I see off the bat is that >the Watermarks read in centibars while the D2K reads in mm of water in a >profile. I am curious how I might easily convert between the two without >doing some gravimetric testing to establish the soil true capacity. Even >then, without testing through many matric potentials to establish a proper >curve, how could I be sure that each unit was responding to soil moisture >in a similar fashion?? >Tom Thomson Northwest Agricultural Consulting >1275 Oak Villa Road tomt@teleport.com >Dallas, Oregon 97338 Phone/FAX 503-623-0468 > >"The only difference between a problem and a solution is that >everyone understands the solution." Charles Kettering > >[Why not compare the two sensors directly in a test bed and allow it to dry >across the range? Bruce] > ___________________ 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/