H Borg

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Permeability, conductivity, conductance and resistance are important parameters in the description of water movement in soils and plants. These terms are related, but not synonymous. Permeability is only a function of the flow pathgeometry of the medium, while conductivity also depends on the fluid involved. Conductance, in addition, takes the size of the medium into account. Resistance is simply the inverse ofconductance. By applying the definition of resistance, it isshown that Darcy's law and Ohm's law are equivalent. Conductance and resistance relate volume flow rate to a potential difference, but to relate volume flux (volume flowrate per unit area) to a potential difference an area specific conductance or an area specific resistance must be used. Permeability and conductivity can be used in both cases. Conductances and resistances are also employed in the description of vapour movement where they relate mass flow rate or mass flux to a concentration difference. Their dimensions are therefore different to those of the analogous terms in thedescription of water movement. However, they can be made identical by introducing proper conversion factors. By doing so, it is shown that Darcy's law and Fink's law are related.

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Soil water, Western Australia, Soil permeability, Plant water relations


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