Improvement of coarse root detection using time and frequency induced polarization: from laboratory to field experiments

Abstract

Over the last decade the induced polarization (IP) method has emerged as a promising tool for subsurface investigation with growing interest for biogeophysics. In this work, in addition to electrical resistivity methods, IP was tested experimentally as a proxy for identifying and discriminating tree coarse roots from the surrounding soil. This study permitted to show the effect of polarization at low frequencies (<25 Hz) using spectral (SIP) and temporal (TDIP) approaches both in laboratory and in the field. (i) the resistivity of woody roots samples was higher than that of a silty soil; (ii) roots polarized at frequencies lower than that of the soil; (iii) the effects of polarization increased with the volume of the buried roots (iv) the direction of roots relatively to current lines influenced the amplitude of IP response. Applying the SIP method in-situ in semi-controlled conditions gave promising results since phase variations around 1 Hz frequency were correlated with buried root position. SIP and TDIP approaches in the lab demonstrated their potential efficiency for detecting coarse roots. This was further demonstrated in the field with SIP. Using maps at several frequencies was useful as variable environmental conditions may change the polarization relaxation frequency and amplitude. Additional works in semi-controlled conditions are necessary to study the dependence of IP response on different parameters of more complex and larger root systems.