Non-destructive estimation of root mass using electrical capacitance on ten herbaceous species

The measurement of electrical capacitance across a root system has been proposed as a quick, affordable, non-invasive and non-destructive method to estimate plant root biomass. Few studies have evaluated this method and of these, most have used plants grown either in hydroponic or sand-based growth media. Our objective was to determine if measures of root electrical capacitance can provide accurate estimates the root biomass of plants grown in soil. Plants of 10 crop and forage species were grown in two sizes of pots (1.5, 4.5 L) containing a fertile potting soil. Each pot contained either one or two individuals and pots were watered to field capacity 1 h before measurements. Electrical capacitance (nanofarads) of the root system was measured and then the root system was extracted. The relationship between electrical capacitance and root dry mass was significant but too weak (r (2) = 0.30) to accurately estimate the biomass of the root systems without prior species-specific calibrations. Root interactions had significant effects on the specific capacitance response, and fine-root species seemed to be more affected. Electrical capacitance in soil-based experiments did not prove as promising as previously shown with hydroponic or sand-based growing media. Targeted root traits based on biological explanations of these capacitor behaviours would need further study to increase the predictive accuracy of this method.