A Custom Soil Electrochemical Profiling System for Detecting Electrochemical Activity Changes in Soil

Physicochemical soil parameters are key drivers of biogeochemical processes, controlling microbial activity and the mobility, solubility, and bioavailability of organic and inorganic matter. These parameters vary with depth, yet tools for their quantification are limited. Microelectrodes, among the most common tools, are primarily designed for biofilms only a few micrometers to millimeters thick and thus unsuitable for centimeter-scale soil gradients. To address this gap, we developed a custom-built automated manipulator system for soil depth profiling. Using off-the-shelf components, we constructed an instrument called Soil Electrochemical Profiling System (SEPS) capable of operating to depths of up to 27 cm with a minimum step interval of 25 µm. SEPS integrates directly with a potentiostat, enabling electrochemical techniques such as redox potential measurements, cyclic voltammetry, and chronoamperometry experiments. We validated the system by generating depth-resolved redox profiles and cyclic voltammograms in soil and sediment reactors. Additionally, we demonstrated its utility for microbial enrichment by polarizing a microelectrode at a fixed depth over 40 days. This system uniquely combines fine-scale automated positioning with electrochemical instrumentation functionality, providing a versatile and affordable platform for soil depth profiling and advancing the study of biogeochemical and microbial processes in terrestrial environments.