| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Dr., Ames, IA 50011 USA
logsdon{at}nstl.gov
Time domain reflectometry (TDR) has been used by soil scientists to determine soil water content (
). A waveform analysis determines an apparent dielectric number (
a) which can often be empirically related to . "Bound water" near colloid surfaces has different properties than free water. At the gigahertz frequencies used for TDR, free water has a negative temperature effect but bound water has a positive temperature effect on dielectric number. Long coaxial cables reduce the higher frequencies of the TDR equipment, which can influence the frequency dependent a of bound water. The objective of this study was to determine the effect of coaxial cable length and temperature on apparent dielectric properties for samples with and without large amounts of bound water. Two undisturbed columns of Okoboji mucky silty clay loam (fine, smectitic, mesic cumulic Endoaquoll) with a specific surface area of 286 m2 g-1 and two packed sand samples with calculated surface areas of 0.01 m2 g-1 were used for the experiment. The a was determined at four cable length combinations, three temperatures, and a range of . The temperature correction factors for Okoboji ranged from 0.008 to 0.012 /°C, depending on cable length. Long cables increased the rise time 41%, which decreased the frequency bandwidth. The Okoboji samples had a bulk electrical conductivity as high as 0.14 S m-1, which hampered determination of the final part of the waveform. In summary for Okoboji, cable length and temperature had a greater effect on a than did . High surface area samples should be calibrated using the same cable length used for measurements, and the temperature effect should be incorporated.
Abbreviations: a, apparent dielectric number, , soil water content • TDR, time domain reflectometry
This article has been cited by other articles:
|
|
 |
|
  M. S. Seyfried and L. E. Grant Temperature Effects on Soil Dielectric Properties Measured at 50 MHz Vadose Zone J., October 8, 2007; 6(4): 759 - 765. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
O. K. Olmanson and T. E. Ochsner Comparing Ambient Temperature Effects on Heat Pulse and Time Domain Reflectometry Soil Water Content Measurements Vadose Zone J., May 26, 2006; 5(2): 751 - 756. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. D. Logsdon Experimental Limitations of Time Domain Reflectometry Hardware for Dispersive Soils Soil Sci. Soc. Am. J., February 27, 2006; 70(2): 537 - 540. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. G. Hunt, S. D. Logsdon, and D. A. Laird Percolation Treatment of Charge Transfer in Humidified Smectite Clays Soil Sci. Soc. Am. J., December 2, 2005; 70(1): 14 - 23. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Logsdon Time Domain Reflectometry Range of Accuracy for High Surface Area Soils Vadose Zone J., November 11, 2005; 4(4): 1011 - 1019. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. R. Evett, J. A. Tolk, and T. A. Howell Time Domain Reflectometry Laboratory Calibration in Travel Time, Bulk Electrical Conductivity, and Effective Frequency Vadose Zone J., November 11, 2005; 4(4): 1020 - 1029. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. D. Logsdon Soil Dielectric Spectra from Vector Network Analyzer Data Soil Sci. Soc. Am. J., June 2, 2005; 69(4): 983 - 989. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Logsdon and D. Laird Cation and Water Content Effects on Dipole Rotation Activation Energy of Smectites Soil Sci. Soc. Am. J., September 1, 2004; 68(5): 1586 - 1591. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. D. Logsdon, S. D. Logsdon, and D. A. Laird ELECTRICAL CONDUCTIVITY SPECTRA OF SMECTITES AS INFLUENCED BY SATURATING CATION AND HUMIDITY Clays and Clay Minerals, August 1, 2004; 52(4): 411 - 420. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. S. Seyfried and M. D. Murdock Measurement of Soil Water Content with a 50-MHz Soil Dielectric Sensor Soil Sci. Soc. Am. J., March 1, 2004; 68(2): 394 - 403. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. A. Robinson, D. A. Robinson, S. B. Jones, J. M. Wraith, D. Or, and S. P. Friedman A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry Vadose Zone J., November 1, 2003; 2(4): 444 - 475. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Nadler, E. Raveh, U. Yermiyahu, and S. R. Green Evaluation of TDR Use to Monitor Water Content in Stem of Lemon Trees and Soil and Their Response to Water Stress Soil Sci. Soc. Am. J., March 1, 2003; 67(2): 437 - 448. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Crop Science | |||
| Journal of Natural Resources and Life Sciences Education |
Vadose Zone Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
