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Burgard, Dan writes to the sowacs list: ===8<============== Doug- I don't recommend trying to convert from soil moisture tension. Tension sensors are an acceptable tool for gauging the availability of the water in the soil for plant use not for determining water content. Cascade Earth Sciences staff have attempted to convert soil moisture tension readings to volumetric water content through calibration to field gravimetric soil moisture content compared to soil moisture readings. We have attempted to do the same thing by using soil moisture release curves developed from a range pressure plate moisture content data. I do not recommend any method as reliable for conversion. The soil water retention curve slope becomes too steep as the soil moisture content approaches field capacity, so a small change in tension readings represents too great a range in volumetric soil moisture. In our experience, soil moisture tension readings are valuable for trend analysis and triggering irrigations based on specific target tension points. It is possible to determine the amount to irrigate at given trigger points with soil water release curves but do not consider any tension-derived volumetric soil moisture content in the range approaching field capacity to be reliable For volumetric water content, capacitance-based sensors are much more reliable. There are several inexpensive capacitance-based volumetric soil moisture sensors are available. I'm sure you'll hear about a few in the responses that you get from your inquiry so I won't go into detail here. Daniel J. Burgard, CPSSc Cascade Earth Sciences dan.burgard@cascade-earth.com (509) 921-0290 voice (509) 921-1788 fax (509) 981-9241 cell Visit our web site at www.cascade-earth.com -----Original Message----- From: Bruce -owner of sowacs [mailto:bruce@sowacs.com] Sent: Saturday, November 29, 2003 1:22 AM To: Bruce Metelerkamp Subject: SOWACS: converting soil moisture tension to VWC Doug Kieffer writes to the sowacs list: ===8<============== I'm curious if anyone knows of any convenient way to do a rough conversion from soil moisture tension to volumetric water content (VWC) if the general soil type is known. So far, I just photocopied a page from my "Intro to Soils" text from college but 1. It only contains 3 soil types (sandy loam, loam, and clay loam) and 2. It's a bit cumbersome. I would be interested in some good (high resolution) moisture release curves or, even better, a simple calculator program where one could enter a moisture tension and soil type and get the rough estimate of VWC. Recent web searches haven't led me to anything so far. Thanks, Doug Kieffer dougkieffer@hotmail.com ===8<============== NOTE: To get off this list, send an email to list@sowacs.com with the subject line: unsubscribe_sowacs For full instructions see this page: <http://www.sowacs.com/subscribe/index.html>