proudly sponsored by
|
archiving of SOWACS proudly sponsored by |
|
NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs Dear Dr. Glenn Brown I have just finished a test of measuring volumetric water content of heavy clay content using TDR (Moisture.Point MP-917). The clay I used is Rideau Clay with no less than 60% of clay content. The electrical conductivity (Ec)of the solution (1:5 soil/water ratio) is approximately 0.10-0.14 dS/m. The probe used is ESI's "C" type probe, 30 cm in length with shorting diode at both ends of the probe. Moisture.Point's patented shorting diode technology provides a reliable relationship between time delay and volumetric water content. When the soil moisture was below 0.35m3/m3, the displayed moisture reading was lower than the actual one because of the effect of bound water (due to its low dielectric constant). When the moisture increased to more than 0.35 m3/m3 then the effect of bound water can be neglected. Moisture.Point provided correct moisture readings up to 0.60 m3/m3. If you are working in heavy clay with a high moisture range, Moisture.Point can be used without special calibration. However, if you are working in a low moisture range, then the theoretical linear relationship between time delay (express as T/Tair) and volumetric water content must be adjusted since the linear relationship doesn't account for the bound water effect. In moderate saline heavy clay situations, something interesting happened. High Ec causes signal attenuation, resulting in over-estimation of water content, and which partially and beneficially compensates for the bound water effect in a low moisture range. However, it leads to an over-estimation when soil moisture is high. A special calibration may solve this problem. I would be more than happy to discuss my experiment and the application of TDR in heavy clay with my colleagues. Jason Sun Ph.D. Research Scientist ESI Environmental Sensors Inc. 100-4243 Glanford Avenue Victoria, BC, Canada V8Z 4B9 Tel: 250-479-6588 Fax: 250-479-1412 e-mail: jason@esica.com <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <META content="MSHTML 5.00.2919.6307" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV> <P><FONT face=Arial size=2><SPAN class=902275321-13042000>Dear Dr. Glenn Brown</SPAN></FONT></P> <P><FONT size=2>I have just finished a test of measuring volumetric water content of heavy clay content using TDR (Moisture.Point MP-917). The clay I used is Rideau Clay with no less than 60% of clay content. The electrical conductivity (Ec)of the solution (1:5 soil/water ratio) is approximately 0.10-0.14<SPAN class=902275321-13042000> </SPAN>dS/m. The probe used is ESI's "C" type probe, 30 cm<SPAN class=902275321-13042000> </SPAN>in length with shorting diode at both ends of the probe. Moisture.Point's patented shorting diode technology provides a reliable relationship between time delay and volumetric water content. When the soil moisture was below 0.35m3/m3, the displayed moisture reading was lower than the actual one because of the effect of bound water<SPAN class=902275321-13042000> </SPAN>(due to its low dielectric constant). When the moisture increased to more than 0.35 m3/m3 then the effect of bound water can be neglected. Moisture.Point provided correct moisture readings up to 0.60 m3/m3.</FONT></P> <P><FONT size=2>If you are working in heavy clay with a high moisture range, Moisture.Point can be used without special calibration. However, if you are working in a low moisture range, then the theoretical linear relationship between time delay<SPAN class=902275321-13042000> </SPAN>(express as T/Tair)<SPAN class=902275321-13042000> </SPAN>and volumetric water content must be adjusted since the linear relationship doesn't account for the bound water effect. </FONT></P> <P><FONT size=2>In moderate saline heavy clay situations, something interesting happened.<SPAN class=902275321-13042000> </SPAN>High Ec causes signal attenuation, resulting in over-estimation of water content, and which partially and beneficially compensates for the bound water effect in a low moisture range. However, it leads to an over-estimation when<SPAN class=902275321-13042000> </SPAN>soil moisture is high. A special calibration may solve this problem. I would be more than happy to discuss my experiment and the application of TDR in heavy clay with my colleagues.</FONT></P> <DIV><FONT face=Arial size=2><SPAN class=902275321-13042000>Jason Sun Ph.D.</SPAN></FONT></DIV> <DIV><FONT face=Arial size=2><SPAN class=902275321-13042000></SPAN></FONT> </DIV> <DIV><FONT face=Arial size=2>Research Scientist</FONT></DIV> <DIV><FONT face=Arial size=2>ESI Environmental Sensors Inc.</FONT></DIV> <DIV><FONT face=Arial size=2>100-4243 Glanford Avenue</FONT></DIV> <DIV><FONT face=Arial size=2>Victoria, BC, Canada</FONT></DIV> <DIV><FONT face=Arial size=2>V8Z 4B9</FONT></DIV> <DIV><FONT face=Arial size=2>Tel: 250-479-6588</FONT></DIV> <DIV><FONT face=Arial size=2>Fax: 250-479-1412</FONT></DIV> <DIV><FONT face=Arial size=2>e-mail: <A href="mailto:jason@esica.com">jason@esica.com</A></FONT></DIV></DIV></BODY>< /HTML>