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Book: Tomography of Soil-Water-Root Processes
Published by: Soil Science Society of America, American Society of Agronomy, and Crop Science Society of America

 

This chapter in TOMOGRAPHY OF SOIL-WATER-ROOT PROCESSES

  1.  p. 135-148
    sssa special publication 36.
    Tomography of Soil-Water-Root Processes

    S. H. Anderson and J. W. Hopmans (ed.)

    ISBN: 978-0-89118-931-2

     
    Published: 1994


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doi:10.2136/sssaspecpub36.c11

Application of Nuclear Magnetic Resonance Imaging to Study Preferential Water Flow Through Root Channels

  1. I-Wen Y. Liu,
  2. Lawrence J. Waldron and
  3. Sam T. S. Wong
  1. University of Californiam, Berkeley, California
    Lawrence Berkeley Laboratory, Berkeley, California

Abstract

Two nuclear magnetic resonance (NMR) imaging techniques, spin echo and gradient recalled echo (GRE) with radio frequency (RF) spoiling, were used to characterize the spatial distribution of bush bean (Phaseolus vulgaris L.) and sunflower (Helianthus annuus L.) roots in plaster of paris columns, 73 mm in diam. and 70 mm in height. The degree of root decay as well as water movement in root channels were observed by sequential NMR imaging studies during 6 months. The average infiltration rate of porous matrix, and the volumetric discharge rate of permeating root channels were also measured during the decay period. High quality NMR images in live roots in situ were obtained with a three-dimensional resolution of 0.4 by 0.4 by 0.6 mm. Root decay reduced the signal to noise ratio of NMR because of dessication and tissue disintegration. Root channels became preferential flow paths after a 4-wk decay period. Dry dead roots were hydrophilic, and could be rehydrated within 5 to 10 min after wetting. Spatial characteristics of roots, such as size, permeation, tortuosity, and orientation of elongation, did not affect the occurrence of preferential flow. The preferential flow velocity approximated from the measured volumetric discharge and the estimated total cross sectional area of permeating root channels was 10 to 50 mm s−1, about 104 to 105 times higher than the average infiltration rate of the porous matrix.

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Copyright © 1994. Copyright © 1994 by the Soil Science Society of Agronomy, Inc., 5585 Guilford Rd., Madison, WI 53711 USA