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Title: SPATIALLY CHARACTERIZING BULK ELECTRICAL CONDUCTIVITY AND WATER CONTENT OF SURFACE SOILS WITH TIME DOMAIN REFLECTOMETRY

Author
item WRAITH, JON - MONTANA STATE UNIV.
item Robinson, David
item JONES, SCOTT - UTAH STATE UNIV.
item LONG, DAN - MONTANA STATE UNIV.

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2004
Publication Date: 3/1/2005
Citation: Wraith, J.M., Robinson, D.A., Jones, S.B., Long, D.S. 2005. Spatially characterizing bulk electrical conductivity and water content of surface soils with time domain reflectometry. Computers and Electronics in Agriculture. 46:239-261.

Interpretive Summary: This article brings together the current knowledge about the spatial mapping of soil water content and soil electrical conductivity at the field scale, using the time domain reflectometry method. The technique has become successful for point measurement at fixed locations but is in its infancy for mobile measurements. We hope some of the results presented in this work will encourage that endeavor.

Technical Abstract: Time domain reflectometry (TDR) has the ability to measure both water content and bulk electrical conductivity (ECa) of soils. From simultaneous knowledge of water content and ECa, the soil solution electrical conductivity ECs and even the concentration of specific ionic constituents such at nitrate-nitrogen may be estimated through soil-specific calibration. This article discusses point, handheld and vehicle-based measurement methods for spatial characterization of soils using TDR. An introduction to TDR measurement principles for determining water content, ECa, and ECs is presented with suggestions for inferring matric potential from dielectric measurements. Applications of TDR to spatially characterize water content in a hilly agricultural field using TDR and gravimetric methods, and to monitor water content and nitrate concentrations at three depths under peppermint production, are presented. The primary limitation of the TDR method for spatially characterizing water content and EC at soil management scales using fixed arrays is the cable length limitation of about 20-30 m. Mobile platforms are of high interest, and prototype designs have been reported in the literature. Truly 'on-the-fly' TDR measurements for large scale applications may be feasible in the near future.