Electrical capacitance of bean (Vicia fabo) root systems was related to tissue density—a test for the Dalton Model

Aims The capacitance method offers a rapid and nondestructive method for root measurement. We tested a four terminal (4 T) capacitance (C, Farads) measurement circuit, which removes parasitic errors. We also tested the plausibility of Dalton Model's assumptions that roots act as cylindrical capacitors and that their entire length contributes to measured C. Methods Faba bean (Vicia faba) was grown in sand and harvested at different ages to determine fresh root mass. Length and radii were determined using scanning software. Tissue density ρ was determined from observing buoyancy in water and from scanned dimensions. Relative permittivity ε r , was calculated using an empirical model fitted to the data. Results Parasitic errors were small. C was a poor predictor of root dimensions. An empirical model L α (C/ρ k ) m , was a reasonable predictor (R²=0.56; P