## 1 Introduction  
Cadmium (Cd) presence in cacao soils is an issue of significant concern within certain areas where cacao is farmed in Colombia [1]. Therefore, diagnostic methods based on soil geophysical properties such as the resistivity of soils should be considered to correlate and understand the dynamics of the metal with other physical and chemical parameters of Cd-enriched areas [2]. Hence, the assessment of parameters such as soil pH, soil organic matter (SOM), soil ionic content of Ca, Fe, and P should be interpreted according to the resistivity responses of Cd-enriched soils. Since the origin of Cd in cacao crops from South and Central America is due mainly to geogenic conditions [3], it is important to develop strategies to perform sensitive diagnosis of Cd using non-destructive and high-throughput approaches. Furthermore, because the distribution of Cd in soils tends to be heterogeneous, assessing the distribution of this metal in subsoil only using spectrometric quantifications is not an easy task. It requires the use of further approaches involving an integrative analysis of the physical, chemical, and micro-biological properties of the cacao farm soil [4; 5; 6]. Regarding the complexity of the potential natural sources of Cd in cacao, both biomineralization and bioweathering have been demonstrated as the biogeochemical processes that influence the rates of availability and precipitation of Cd in soil solution, which may define the ratio of assimilated Cd into the cacao trees [1]. Although the specific mechanisms involved in each of the above mentioned processes remains unknown and may vary on the biological aspects of the biogeochemical pathway (i.e., due to the key role of bacterial metabolic capacities to deal with Cd at the subsurface), the interaction of both biological and chemical factors occurs frequently and influences Cd debris throughout the system. Thus, a proxy to study its distribution and dynamics should be inferred through the physical changes of Cd-like compounds present in enriched or contaminated soils. Some geophysical studies have noted the use of two-dimensional electrical resistivity tomography (2D-ERT) to analyze the composition of rocks or mineral outcroppings related to cadmium in the subsurface of bulk-type soils [7; 8; 9]. The use of the 2D-ERT technique can be considered for determining Cd in cacao for at least three reasons: One, it is a non-invasive, non-destructive technique [7], which determines the mineralogical content of Cd-like solid-phase compounds in subsoil. Second, because cacao farm soils are extremely heterogeneous in physical properties, the study implies the integration of resistivity measurements with the intrinsic physical-chemical composition of soil using parameters such as pH, SOM, and ionic Ca/Fe/P ratios. Third, 2D-ERT is a technique that differentiates geological structures based on resistivity profiles and visualizes Cd outcroppings occurring in situ. The 2D-ERT method uses electrodes distributed along a line. Each electrode is connected to others, allowing an electrical current flow in soil depth [10]. The distribution of the electrical flow occurs due to the disposition of two electrodes at the soil surface. The determination of resistivity at the subsoil surface is obtained using another pair of electrodes. Thus, the magnitude of the measurement primarily depends on the distribution of resistivity in the subsurface soil structure, the distance between the paired electrodes supplying the electrical signal and the flow of electrical current [8; 11]. The theory behind resistivity measurements related to the use of [PERSON]'s law that is determined by an electrical signal of current. Applying the Wenner method of electrode configuration it is possible to map the resistivity at each discharge with high sensitivity and accuracy [12], and it is possible to preselect zones at the subsurface with resistivity related to clay content and the underlying geological parent material [13].