Plant and Soil

, Volume 75, Issue 2, pp 153–168 | Cite as

Physical model of water in a split-root system

  • M. B. Kirkham


A physical model, based on Darcy's law and an Ohm's-law analogy, was developed to show that water can move from a wetter side of a root system to a drier side or vice versa. In the model, a wick in the form of an inverted Y was used, with the two ends of the Y in separate beakers and the third end (stem) of the Y extending into the air. The left root, right root, and stem were about 6,5, and 4 cm long, respectively. The difference in total head (potential) between the left root and the right root was varied for different potentials applied to the stem. Experiments were done either in a darkened laboratory or with a sunlamp shining on the stem. The stem was thus exposed to low-evaporation (in the dark) or high-evaporation (with the sunlamp) conditions. Total heads (sum of head due to gravity and head due to pressure-other heads were negligible) and flows of water were calculated or measured for each part of the split-root system (left root, right root, crown, stem). The results showed that the direction and quantity of water flowing in each part of the system depended upon the total head for the stem, crown, and each half of the root (the flow could be up, down, left, or right), and that the gravity component of the total head was important in moving water down the plant when light intensity was low.

Key words

Crown Darcy's law Gravity head Ohm's-law analogue Porous medium Potential flow Pressure head Reverse transport Split roots Streamlines Total head Water potential Wick 


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Copyright information

© Martinus Nijhoff/Dr W. Junk Publishers 1983

Authors and Affiliations

  • M. B. Kirkham
    • 1
  1. 1.Evapotranspiration LaboratoryKansas State UniversityManhattanUSA

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