Optimisation of an ERT acquisition for soil-plant interaction in presence of biochar

In the mitigating strategies of human impact on environments, the biochar addition to shallow soil horizon represents a promising way among the existing Carbon Dioxide Removal technique. This study is part of a project that aims at evaluating the impact of the presence of biochar in soils on the growth of roots. Geophysical techniques are a good candidate for non-invasive investigation and field monitoring. Among the existing techniques, Electrical Resistivity Tomography (ERT) has already shown great potential for detecting the presence and growth of roots in agricultural soils.

In this study, our goal is to test whether ERT is able to track changes in root growth in a technosol. The field experiment takes place on a setup consisting of 20 plots of 2 meters by 3 meters where the first 0.3 meters were disturbed and for half of them biochar has been incorporated (ca. 2% wt.). As we are expecting 3D effect on this specific field (effects of the limits of the plot, effects of the roots), we design a numerical study to determine the best experimental setup for a 2D ERT profile using pyGIMLi, an open-source software library for geophysical inversion.

We conducted several numerical simulations to determine the optimal dimensions of a meshed body, which was considered as a semi-infinite space, to simulate profiles of 48 and 96 electrodes separated by 0.1 meters. Field measurements on plots with and without biochar showed electric resistivity values of 45 ohm m and 56 ohm m, respectively, suggesting that ERT might be able to detect the biochar presence. Using this information, we focus our numerical simulations on a suitable configuration to assess the effect of biochar onto root growth.