Impact of Maize Roots on Soil-Root Electrical Conductivity: A Simulation Study

Electrical resistivity tomography (ERT) has become an important tool for studying root-zone soil water fluxes under field conditions. The results of ERT translate to water content via empirical pedophysical relations, usually ignoring the impact of roots; however, studies in the literature have shown that roots in soils may actually play a non-negligible role in the bulk electrical conductivity (sigma) of the soil-root continuum, but we do not completely understand the impact of root segments on ERT measurements. In this numerical study, we coupled an electrical model with a plant-soil water flow model to investigate the impact of roots on virtual ERT measurements. The coupled model can produce three-dimensional simulations of root growth and development, water flow in soil and root systems, and electrical transfer in the soil-root continuum. Our electrical simulation illustrates that in rooted soils, for every 1% increase in the root/sand volume ratio, there can be a 4 to 18% increase in the uncertainty of a computed via the model, caused by the presence of root segments; the uncertainty in a loam medium is 0.2 to 1.5%. The influence of root segments on ERT measurements depends on the root surface area (r = similar to 0.6) and the a contrast between roots and the soil (r = similar to 0.9), as revealed by correlation analysis. This study is important in the context of accurate water content predictions for automated irrigation systems in sandy soil.