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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 Reply to Tom Thompson. You can be 100% assured that the measure of soil water from the Sentek device and from the water mark device are NOT the same. The Sentek outputs (via a built in calibration) volumetric water content in cc/cc , the Watermark outputs (again via a calibration - maybe built in maybe not) a measure of the soil water suction (usually in kPa). The conversion between these two measures of soil water is the moisture retention curve. The shape of this curve is dependent on the pore size distribution of the soil, so is quite different for a sand and a clay. The measurement of this curve is a routine process in any soils physics laboratory or basic texts in soil physics usually give approximate 'generic' curves for eg a 'sandy loam'. I recommend you get a basic soil physics textbook and read up on it. cliff.hignett@ soilwater.com.au owner-sowacs@aqua.ccwr.ac.za 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] -- Cliff Hignett Soil Water Solutions 45a Ormond Ave Daw Park South Australia 5041 pH 61 (08) 8276 7706 WWW.SOILWATER.COM.AU