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A pair of stainless steel probes inserted in the soil will always be subject to the effect of salinity (from any source, including fertilizer salts), when used to measure a resistance value for purposes of estimating soil water status. The Aquamiser would be an example of this. Perhaps the Center for Irrigation Technology in Fresno, California, has done evaluation of the Aquamiser, as they ran a study several years ago on a variety of soil moisture sensors. You could contact David Zoldoske, Director, at: davidzoldoske@csufresno.edu and ask him. A newer resistance type technology is embodied in the Watermark sensor which is manufactured by our company. It was designed to overcome the principal limitations of a gypsum block--those being the fact that the gypsum encapsulation (which is a buffer for salinity) dissolves in the soil and can destroy the reading accuracy, individual blocks have unique calibrations, and they typically are not sensitive in the wet end of the soil water range ( <50 kPa ). The Watermark has been investigated for over 10 years by the scientific community, and is often referred to as a Granular Matrix Sensor (GMS). A website of interest here would be that of Oregon State University's Experiment Station at Ontario, OR, where, under Granular Matrix Sensors, a good bit of reference information can be obtained ( http://www.primenet.com/~mesosu). Use of a DC power source to read such a device must be carefully timed so as to avoid bubbling of the electrodes. The Watermark utilizes an AC resistance bridge type meter to avoid such a problem. Further, I fear that constant power applied to a pair of electrodes imbedded in moist soil would certainly cause electrode damage (galvanic action), thus practically destroying the sensor. Here in the US, Rain Bird Sales has been marketing the Aquamiser, but has recently made the decision to discontinue the marketing effort. In South Africa, our company's products, including the Watermark, are distributed by a company called CALAFRICA. You could reach Rodney Mountain in the Cape area (Erinvale) at: (21) 847-1215, or Mike Hill in the J'Burg area at: (11) 452-1790. Contact me directly at irrometer@aol.com if you'd like additional information, or visit our website at http://www.irrometer.com. Regards, Bill Pogue, President, Irrometer Company Inc., Riverside, CA (USA)