Nacsa Tibor

A known electrical measuring method for the examination of living root systems in soil is applied and a further root-soil capacitance model was developed. A two dielectric media capacitors model is recommended as extension of Dalton’s root-soil resistance-capacitance model. The extended model involves and evaluates the effect of soil and soil water status in root capacitance differently from the resistance-capacitance models. The frequency dependence of capacitance measured for a sunflower root in soil, a piece of the washed out root and the soil root medium was also studied. The capacitance of the sunflower root in soil was found smaller than that of the soil and higher than that of the root piece at 1 kHz. Phase-lead angles of the HP4284 instrument’s measuring signal at 1 kHz showed a rather capacitive character for the sunflower root piece and root in soil. However, in spite of the relatively high capacitance of the soil at 1 kHz its phase-lead angle was smaller than that of the root, so capacitive character of the soil seemed rather weak. Root capacitances of sunflower plants indicated nicely the development of root mass at each growth stage measured with either the needle or clamp plant electrode. The mechanism of polarization is explained for the clamp plant electrode via the electric field of the capacitance meter. Root capacitances of sunflowers measured with clamp and needle plant electrodes were only similar when roots of the sunflower plants were placed in water. Their difference increased with decreasing soil water content. The root mass correlated better with root capacitances measured either with needle or clamp plant electrode than the root length. Generalization of the presented results requires further investigations.