Probing Soil Electrochemistry: Electrochemical Characterization of Soil Via a Faradaic Approach
Authors: Dhamu Vikram Narayanan , Paul Anirban , Muthukumar Sriram , Prasad Shalini 
Published: May 2020

Soil is a vital component that holds together the Earth’s ecosystem. It plays an active role in biological events, hydrologic (water) cycle and behaves as a sink-source system for greenhouse agents (gases). More so, soil directly impacts growth of plants, crops and other vegetation. Commercially, soil quality determines the yield and type of farmland-wherein it is essential to have thorough information about soil parameters that is synchronized in terms of geological location (space) and period (time) due to variations associated with global change and land use. Implementation of soil sensors would be fundamentally beneficial to characterize the soil parameters in a local as well as global environmental-impact standpoint. Assessment of these parameters in soil samples in farm setting facilitates quantification and recording of its inherent physical and biochemical characteristics. Sufficient levels of soil nutrients is required for sustainable agricultural practices that typically exists as crop yield, pasture growth, etc. Currently, soil sampling and evaluation methods involve destructive and intrusive approaches to collect and then subsequently test the soil samples. Among this-Combustion method is one of the most widely sought after techniques to look at soil anatomy. Even with the upcoming research breakthroughs in non-destructive approaches like spectroscopy and tomography based models, there is a barrier in-terms of equipment complexity and availability as well as high costs and high logistical overhead. Therefore a sensing based ‘bottom-up’ approach is proposed in this study to probe soil matter and nutrient content. Soils are known to be dynamic systems under natural conditions and implementation of an integrated electrochemical and analytical chemistry methodology offers the added advantage of evaluating soil properties on-demand and in situ. Another main advantage of an electrochemical-analytical approach and the novelty of the proposed platform lies in the ability to profile soil at an interfacial level using a probe system and characterize the matrix in order to provide information in terms of various physico-chemical phenomena occurring at the electrode interface and correlate that to useful data that helps to understand soil fertility and bio-availability of nutrients for plants and other vegetation at the field level. There are a wide number of redox systems present in soil that exist in reduced state under ideal conditions (submerged). Soil is known to contain considerable amounts of these reducing substances as a function of organic matter content. In this work, faradaic measurements are utilized to determine threshold changes in soil electrochemical activity due to presence of various redox active substances present in the matrix. From preliminary data (Fig.1) and literature studies, there seems to be a high-correlation between electrochemical activity and presence of active substances that contribute to the soil-nutrient cycle which in turn differs in terms of various soil types. Therefore, probing these parameters could give further insight as to what in particular in the soil matrix contributes to the overall properties of soil type of a specific region. Results from this experimental question is used to track if confident deductions can be made with respect to constituency of soil matrix, assessing soil type, bulk density (BD), cation exchange capacity (CEC), electrical conductivity (EC), and electrochemical activity as a function of spatial and depth changes among other parameters.

Figure 1