Toward characterization of organic matter rich in aromatic compounds by spectral-induced polarization: preliminary investigation and perspectives

SUMMARY Spectral induced polarization (SIP) has been suggested as a non-invasive and cost-effective tool to detect and monitor aromatic rich organic matter such as biochar. In our study, we show that SIP can track biochar concentration up to 10 per cent (wt.) in a soil with a clay content of 20 per cent. Assessment of changes in the concentration of biochar was conducted according to double Pelton parameters and the maximal phase determined at 11.7 Hz, a frequency at which a polarization peak is observed in the presence of biochar. All SIP-derived parameters were correlated with the biochar content, with the exception of the relaxation time of the polarization peak occurring at 11.7 Hz, which was related to soil water saturation in previous investigations. Among studied parameters, the phase value that we measured at 11.7 Hz may therefore consist in a simple and reliable methodology to evaluate the biochar content on SIP in our experiment. Several steps are still necessary before a widespread field application notably by considering how modifications in the chemistry of biochar with time can interact with biochar concentration and water saturation to modify polarization processes shaping SIP curves. Beyond the scope of tracking changes in the content of highly aromatic OM—such as biochar—in soils, this study suggests that the degree of aromaticity of OM can play a key role in the SIP response paving the way for wider use of SIP in soil science.