Following what may have been an unfair put-down of the Watermark sensor, I have put together the following from comments I have received: Bruce Metelerkamp's original comment: "I have tried various sensors for use with continuous datalogged systems, but these did not have the required range and/or ruggedness. Gypsum blocks are the worst, followed closely by nylon blocks, Watermark sensors and heat dissipation sensors." Tony Thomson's comment: "1. Watermark = Granular Matrix Sensor does not work in coarse texture (sand) soils" However, there have been numerous (countless?) recorded succesful applications of the Watermark: From Dr Clint Shock: " We have also had success with Watermarks for a longer time." Peter D. Spyke commented: "We have talked to Bill Pogue (Irrometer) about the Watermark in Florida, where our soils are extremely sandy (most of it is prehistoric beach front). Since our tension ranges are so low, the Watermark may not sense accurately in the lower range. Bill recommended that we try the new Low Tension (LT Model) Irrometer. We had been using standard Irrometers for 10 years with good success. However, the LT has proven to be much more accurate under our conditions since the ceramic tip is more porous. We are finding as much as a two day lag time between the standard models and the LT's." The manufacturer of the sensor Bill Pogue of Irrometer had the following to say: "Of concern to us is the fact that our technology, particularly WATERMARK, be given fair treatment, and your message of 4/26 is a case in point when you state that your evaluation did not( produce) " good results". Our product is intended to inexpensively track soil water potential in soils with reasonably good non saturated hydraulic conductivity. The plant roots remove water from the soil pulling water out of the sensor. As the sensor dries, the sensor resistance increases to the point that the irrigator can tell that irrigation is warrented. Thousands of customers around the world have soil where WATERMARK resistance increases and decreases consistentlywith the wetting and drying of the soil. WATERMARKS provide thesegrowers with a practical and reliable way to track soil water potential tomake irrigation decisions between 10 and 70 kPa. In addition, it is ofconcern to me that you base your evaluation of WATERMARKS on data frompressure pots. WATERMARKS have been reported to have mixed results in pressure pots over the years, in the same soil series where they have consistently good field and weighing lysimeter performance. I am not a soil scientist, nor an engineer, but am concerned that limitations or problems with "methodology" of sensor evaluation sometimes have cast doubt on the operational behavior of the WATERMARK. Steve Thomson at Virginia Tech has used "pot" analysis with WATERMARKS for over ten years, and Thomson and Armstrong (1987) has been the standard calibration for this period of time. Clint Shock at Oregon State University, over the same period, has validated WATERMARK behavior in weighing lysimeters and in field plots---he places nocredence in "pot" analysis. But, Shock and Thomson pretty well agree.We are working with both of them now on an experimental non-linearcalibration for our hand held meters, which it is felt is closer to thereal world operation of the WATERMARK--- especially in the lightersoils. We are talking about ten years + of investigation, and tens of thousands of data points with hundreds of different sensors produced overthis ten year span. So when someone reports that the WATERMARKsensor does not behave in a "thus and so" manner, my reaction is thatsomething has been "lost in translation". Please be advised that several journal published articles on WATERMARKS have serious flaws. We shouldavoid major errors being published in a scientific journal, let alone in"cyberspace". Please consider also that there are some inherentproblems with "expectations", which can vary greatly depending on the individual involved and what it is in the way of required data. A soilphysicist vs. an agronomist vs. a farmer----they all have different needs---and even within a single category there may be a whole variety of needswhich differ from one another due to the nature of the "investigation". Clint Shock at OSU has one which includes some information on GranularMatrix Sensors (WATERMARK), and a number of important references for someone who's interested. You may want to take a look at it:http://www.primenet.com/~mesosu/ In summary--- the WATERMARK will not fit each and every conceivableend use in the field of "soil water status measurement". But if you are trying to make a decision concerning irrigation scheduling withinthe realm of a "well watered crop", then the WATERMARK becomesa very important consideration. Like my Chevrolet automobile, it won't win the Indianapolis 500, but it sure provides a pretty dependable form of transportation. And it is far less expensive and practical. Regards, Bill Pogue, President, Irrometer Company, Inc." Well said Bill, and point taken! Bill, may I take you up on your offer now to post a list of references and reports detailing the good character of your Watermarks? In my defense, I was [more of] a novice when I made these observations, and I was (and still am after a sensor that works reliably over the entire wet to dry range - a tall order indeed. I now feel that fair justice has been given to the topic - but please feel free to vent positive and negative feedback.I'was [more of] a novice when I made these observations, and I was (and still am after a sensor that works reliably over the entire wet to dry range - a tall order indeed. I now feel that fair justice has been given to the topic - but please feel free to vent positive and negative feedback. I'm sure Bill will post you commercial info if you contact him at Irrometer@aol.com -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. Bruce Metelerkamp SOIL WATER RESEARCH OFFICER Host of SoWaCS (Soil Water Content Sensor) Discussion List sowacs@aqua.ccwr.ac.za