Non-invasive acoustic sensing of belowground wooden tissues: Possible application to spatial mapping of soil usage by tree roots

Growth of roots are central to the physiology and ecology of terrestrial higher plants including forest trees and agricultural crops. Ecologists, ecohydrologists, and biogeochemists need detailed insights into belowground properties and processes where plant roots take place, including changes in water, salts, and other elements that can influence ecosystem productivity and functioning. While growth and development of root system are dynamic, its status is hardly understood since roots grow belowground thus invisible with any optical means. In this study, we attempted to apply acoustic means for detection of undersoil tree roots, by developing a novel non-invasive sensing technology for detection of belowground plant tissues based on sound propagation in the soil. Novel instrumental set-up was designed for modulation and demodulation of sound signals passed through soil or sand with and without wood or tree roots. We detected the presence of wooden cut pieces and a living tree root both hidden belowground. This first attempt may induce further studies and developments by scientists and engineers for belowground sensing and imaging techniques as novel ecological research tools.