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Agronomy Journal Abstract -

Axial Resistance to Water Flow of Intact Cotton Taproots


This article in AJ

  1. Vol. 87 No. 3, p. 439-445
    Received: Apr 2, 1992

    * Corresponding author(s):
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  1. Akira Yamauchi,
  2. Howard M. Taylor,
  3. Dan R. Upchurch  and
  4. Bobbie L. McMichael
  1. S chool of Agric., Nagoya Univ., Chikusa, Nagoya 464, Japan
    ( deceased), Dep. of Agronomy, Horticulture, and Entomology, Texas Tech Univ., Lubbock, TX 79409



A knowledge of root hydraulic resistance is required for the application of water flow models of the plant-soil system. An attempt was made to estimate axial resistance of intact cotton (Gossypium hirsutum L. cv. Tamcot CAMD-E 107-5A) taproots to water flow by direct and simultaneous measurement of water Ilow rate and of the gradient in xylem water potential. Fiscus's root psychrometer was modified and used for the measurement of xylem water potential. The measurements were made in rigidly controlled, constant temperature environments, and under conditions in which no water was available for the portion of the taproot where xylem water potential gradient was measured, but water was available distal to that portion. The water uptake rate was simultaneously measured while water was supplied at a constant head. Axial resistance to water flow along a cotton taproot of 70- to 120-d-old plants was on the order of 1 mg−1 water m−1 root s MPa, which is near the lower limit of published values for cotton and other species. Axial resistance was also calculated from the measured xylem vessel diameters based on the Poiseuille-Hagen equation. Measured axial resistance values were ≈ 20 times those calculated using the Poiseuille-Hagen equation. It required as long as 34 d for the water potential inside the psychrometer chamber to equilibrate with that of the root xylem. Drying the root substantially increased the radial resistance and thereby increased the time required for equilibration. Modifications to the described experimental apparatus and procedure will be required.

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