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Title: MINIMIZING DRIFT IN ELECTRICAL CONDUCTIVITY MEASUREMENTS IN HIGH TEMPERATURE ENVIRONMENTS USING THE EM-38

Author
item Robinson, David
item LESCH, SCOTT - UC RIVERSIDE, CA
item LEBRON, INMACULADA - UC RIVERSIDE, CA
item Shouse, Peter

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2003
Publication Date: 3/1/2004
Citation: Robinson, D.A., Lesch, S.M., Lebron, I., Shouse, P.J. 2004. Minimizing drift in electrical conductivity measurements in high temperature environments using the em-38. Soil Science Society of America Journal. 68:339-345.

Interpretive Summary: The EM-38 is a portable electromagnetic device used for measuring bulk soil electrical conductivity. The measurements are used to estimate soil salinity in agricultural fields to assist growers in choosing a crop or for assessing salinity levels for land reclamation. We have found during use of the instrument in the arid southwestern United States that readings at the start of the day and end of the day when replicated do not always match. This experimental study suggests that increased instrument temperatures in excess of 40 degrees might be to blame. One solution is to shade the instrument from the sun, which can reduce instrument working temperatures by 20 degrees.

Technical Abstract: The Geonics EM-38 is a commonly used tool for non-invasive mapping of ground bulk soil electrical conductivity (ECa). Mapping use includes, soil salinity, soil texture and water content maps within precision agriculture. In the southern United States instruments are used in the summer where shade temperatures can reach 50oC. In this extreme environment it is important to understand how such temperatures affect instrument response. In this work we demonstrate that the instrument is affected by elevated temperatures, which initially increase the EM response and then reduce it as temperatures rise further. In laboratory work the instrument appeared to be compensated to a temperature of 40 degrees, above this temperature we show that the response of the instrument is unpredictable, first rising and then dipping as temperature continues to increase to 60 degrees. We believe that this accounts for the so-called 'drift' behavior of the instrument, which has been observed by users in the arid southwestern United States. We find that a simple and practical solution to this problem is to shade the instrument, this can reduce the instrument panel temperature by as much as 20 degrees when left out in the sun. Field results suggest that it is best to maintain the instrument temperature below 35 degrees to ensure that the instrument temperature compensation is fully working and that the measurement response is due solely to ground conductivity as required.