A conceptual model is presented that provides a rational basis for using plant root capacitance as an in-situ measurement for assessing plant root development. This method is based on measuring the electrical capacitance of an equivalent parallel resistance-capacitance circuit formed by the interface between soil-water and the plant root surface. Nutrient solution studies using tomato (Lycopersicon esculentum Mill.) showed a good correlation between plant root capacitance and root mass. Stage of development studies showed plant root capacitance measurements capable of detecting root development rate and suggested the method to be sensitive to root function. Soil water content was shown to have a significant effect on plant root capacitance measurement. The possibility of using this technique to assess relative root function is discussed. Positioning of the plant shoot electrode was shown to also have a significant effect on measurement of plant root capacitance, demonstrating the need for using consistent measurement techniques. The electrical capacitance method shows considerable promise. More research is needed before it can be used routinely.

Two parallel metallic rods were used as a wave guide to measure the dielectric constant and electrical conductivity of soils having different electrical conductivities but the same water content. Measurements showed that the two parameters were sufficiently independent to permit simultaneous determinations of water content and bulk electrical conductivity.

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A theory describing the hydraulic and osmotic transport of water and the diffuse, convective and active transport of solutes across root membranes is formulated. The theory predicts the dependence of the ratio of the osmotic pressures of the nutrient and xylem solutions and of the solute flux upon the rate of water uptake. The theory also predicts a nonlinear relationship between the flux of water and the pressure difference across root membranes. The results are shown to be in good qualitative agreement with a variety of observations on simultaneous uptake of water and solutes.