A custom soil electrochemical profiling system for detecting electrochemical activity changes in soil

Physicochemical soil parameters drive biogeochemical processes by controlling microbial activity and the mobility, solubility, and bioavailability of organic and inorganic matter. Because these properties vary with depth, depth-resolved electrochemical tools are needed, yet existing systems are often limited in travel range, automation, cost, or flexibility. Here, we present a custom-built Soil Electrochemical Profiling System (SEPS) for water-saturated soils and other conductive porous media. Built from off-the-shelf components, the custom manipulator hardware can be assembled for less than $200, provides up to 27 cm vertical travel, and operates with a minimum mechanical step interval of 25 μm. SEPS integrates with a potentiostat to perform open-circuit-potential-based redox profiling, cyclic voltammetry, and chronoamperometry. We tested the system using ferricyanide/ferrocyanide standards and hydrogel diffusion experiments. We then demonstrated proof-of-concept applications in homogenized, water-saturated soil mesocosms, where SEPS resolved time- and depth-dependent redox changes and voltammetric responses. In addition, a polarized carbon-tip electrode supported long-term biofilm enrichment and subsequent depth-resolved chronoamperometric measurements. SEPS provides a practical, low-cost platform for electrochemical profiling in saturated soils, hydrogels, sediments, and related porous media.