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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 >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. To get an accurate calibration you are going to need 10-20 gravimetric samples at both the dry and wet end. If it is non-linear you will need more For volumetric soil moisture you also need accurate bulk densities And all that repeated for each soil type... Because if it is *not* done properly you could well be less accurate doing your own calibration rather than using a 'standard' There are several examples of steering committees insisting on re-calibration of soil moisture sensors, and the resulting equations probably gave less accurate results than using 'standard' equation. (never mind that the projects spent a great deal of time calibrating and not actually taking and analysing measurements...) ----- After a rainfall, is the recorded change in soil moisture what you would expect ? Because unlike many other things we measure, rain volumes can be checked using tin cans. -------- Trevor Finch Research Services New England 8/16 Nicholson Street Balmain NSW 2041 Australia tel: +61 (2) 9810 3563 fax: +61 (2) 9810 3323 mailto:support@rsne.com.au ----------