## 5 Conclusions  
The use of the 2D-ERT technique to assess soil Cd distribution is feasible and well correlated with Cd quantification using ICP-OES. The 2D-ERT technique increase its function when it is analyzed with the biogeochemistry of the assessed soils. The technique could be used to compare Cd with physical parameters as an excellent strategy for Cd surveys in cacao farms as a first proxy, where cacao farmers require cost-effective/non-destructive techniques to carry out diagnoses and develop strategies to tackle the Cd issue. Indeed, the more lines of 2D-ERT that are carried out, the more accurate this proxy becomes in detecting the location of Cd solid-phase materials present in cacao farm soil. Thus, this technique is an excellent approach to assess the rhizospheric Cd content in cacao farms. Additionally, the method is well correlated to soluble and non-soluble sources of Cd when calibrated, sources that could occur at any point during Cd cycling in cacao systems. In the Araucan farms, the 2D-ERT technique could be used to predict agricultural practices that need to be revised such  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Method** &
\begin{tabular}{c} **Accuracy of Cd** \\ **Measured [mg-kg-1]** \\ \end{tabular} & **Source** \\ \hline \multirow{4}{*}{in situ} & Magnetic susceptibility measurement & 0.12–0.27 & [39] \\  & CaCl\({}_{2}\), EDTA, and DGT with ICP-AES & 0.11–2.57 & [40] \\  & Portable X-ray diffraction fluorescence measurement & 0.06–1.60 & [41] \\  & 2D-ERT and ICP-OES & 0.03–2.76 & This study \\ \hline \multirow{4}{*}{in laboratory} & SOM, clay, and pH as predictors & 0.1–4.1 & [42] \\  & Geostatistical (kriging interpolation) combined with & 0.12–1.62 & [43] \\ \cline{1-1}  & \multicolumn{2}{c}{(H) Graphite furnace atomic absorption spectroscopy.} \\ \cline{1-1}  & & & \\ \end{tabular}
\end{table}
Table 2: Cd detection using several methods in agricultural soils.  
as fertilizer management, to decrease external inputs of Cd and as well as the removal of geological outcrops. In contrast, for the farms located in Muzo and San Vicente de Chucuri, in the Boyaca and Santander districts, respectively, site-specific Cd in subsoil should be treated according to the dynamics of the system, and the biological Cd available fraction of soils and edaphoclimatic conditions of such locations considered at a farm scale.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/12/4149/s1](http://www.mdpi.com/2076-3417/10/12/4149/s1)]([http://www.mdpi.com/2076-3417/10/12/4149/s1](http://www.mdpi.com/2076-3417/10/12/4149/s1)).  
Both authors contributed equally in conceptualization, methodology, formal analysis, writing--original draft preparation, writing--review and editing, visualization, supervision, and project administration. [PERSON] was responsible for funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Corporacion Colombiana de Investigacion Agroposcuria AGROSAVIA, through Grant No. 417, as part of the project entitled \"Cd in cacao and the strategies to tackle it\".  
The authors would like to thank to the Colombian Ministry of Agriculture and Rural Development (MADR) and the Corporacion Colombiana de Investigacion Agroposcuria AGROSAVIA for supporting this study. The soil samples were collected according to the Colombian Resolution No. 1466 of 3 rd December 2014, by which Agrosavia has permission to collect of biological diversity samples for non-commercial and scientific research purposes. We also would like to thank to [PERSON] for proofreading this manuscript, to [PERSON] for advising during soil classification, and to the anonymous reviewers for their kind suggestion to improve this manuscript.  
The authors declare no conflict of interest.