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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 owner-sowacs@aqua.ccwr.ac.za wrote: > > > >Claims have been made that a 'generic' calibration equation will yield the same CHANGE in water content/ depth of a summed profile as a site specific calibration curve but will have different absolute values. This means that a generic equation is just as helpful in determining such measurements as plant water use as a site specific equation. ... < < < > To SOWACS: The use of a generic calibration to determine relative change in soil water content from one period to the next does not require an accurate absolute water content - PROVIDED THAT ANY ERROR IN INDICATED SOIL WATER CONTENT DUE TO THE GENERIC CALIBRATION ERROR IS CONSTANT OVER THE MEASUREMENT RANGE. My own experience has been a lot less lucky, that is, calibration errors varied from dry to wet and were greatest in the wet end. The calibration also shifts with a change in salinity. I would recommend checking the generic calibration over the expected soil water content measurement range gravimetrically and then (since you have the calibration data on hand) develop your own calibration equation. Thanks R. Louis Baumhardt, Soil Scientist USDA-ARS Conservation and Production Research Laboratory P.O. Drawer 10 Bushland, TX 79012 Phone:(806)356-5766 FAX: (806)356-5750 email: lbaumhar@ag.gov