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Bill Pogue of Irrometer (suppliers of Watermark sensors) writes: Dear Ms. Lawson: I read your posting on Irrigation-L requesting information on the comparison between the concept of rain cut-off devices and soil moisture based control devices. Our company has manufactured the latter since 1951, and there is practically more background (5-8 decades worth from the scientific community and users) than I could ever go into here. In short, soil moisture based scheduling is proven and effective. How much water can you save??? It purely depends on how "good" or "bad" the irrigation scheduling job being studied as a comparison truly turns out to be. A much more valid comparison can be seen in the ASAE paper, DeOreo and Lander, 1994. Automated Irrigation Scheduling Using Soil Moisture Sensors, Paper No. 94-2119, ASAE, St. Joseph, MI. And even more updated thru 1997 by DeOreo's staus report on this project done in/for the City of Boulder, CO. In this, the use of the WATERMARK soil moisture sensor control system from Irrometer Company clearly has performed over a period of about 5 years, and has practically automatically con- trolled irrigation very close to the ET model (consumptive use of the plant material). What this means, is that irrespective of how much beyond the "crop need" for water was programmed into the controller, the WATERMARK system clearly LIMITED the amount of water actually applied to that which was actually needed. If you would like copies on any of these reports, we can furnish them on request. And, Bill DeOreo of AQUACRFT Water Engineering (copied here), would be more than happy, I'm sure, to consult with you further. His principal business is consultancy, and he has done a good number of water use studies for water purveyors including municipal owned water supply systems. So, what about rain cut-off devices? They basically work to limit an irrigation event when rainfall has been adequate to trigger them. BUT, beyond that, they do nothing to "schedule" irrigation in an automatic mode for the days which do not experience rainfall (and maybe the day after while the rain sensing device is drying out). Certainly better than nothing I suppose, but sort of like getting a "half of a loaf", when just a few more dollars can get you the "entire loaf". The soil moisture sensor certainly "sees" the rainfall in the soil (as seen from the Boulder work where they disabled irrigation perfectly during rainfall events), but then they also "see" when it starts to dry out, so that irrigation would be permittted at the appropriate time. Further, the Center For Irrigation Technology, Fresno, CA, has done invesitgative work on the efficacy of a variety of soil moisture measuring technologies, and the WATERMARK has come up with very good "grades". You may want to talk to David Zoldoske, Director (209) 278-2066 (david_zoldoske@csufresno.edu) if you'd like specific information from CIT. Finally, our website is: http://www.irrometer.com which gives some overview of our company and its technology. While there, in the NEWSLETTER section, you can hyperlink to Dr. Shock's website (Oregon State University) and under Granular Matrix Sensors, get a good bit more in terms of published references for the WATERMARK. I can also mail you additional product and cost information, besides the referenced reports above. Regards, Bill Pogue, President, Irrometer Company Inc. Riverside, CA