Application of electromagnetic induction and inversion modelling for 3D mapping of soil texture

Abstract

Using a DUALEM21 sensor, we conducted electromagnetic induction (EMI) surveys in an agricultural field in the Roxo irrigation perimeter in Alentejo, Portugal, to evaluate the potential of using this technique for 3D mapping of soil texture. We first processed apparent electrical conductivity data (EC_a) and then used a Quasi-3D inversion algorithm in order to obtain 3D electromagnetic conductivity images (EMCI) of the actual bulk soil electrical conductivity (EC). This is because the EC_a is a depth-weighted, average conductivity measurement and does not represent the actual EC variation with depth. Afterward, we evaluated the possibility of establishing a linear regression (LR) relationship between EC and soil texture collected from 13 soil sample locations at 3 layers to a depth of 0.60 m. We selected the locations for soil sampling based on the EC_a variations. Our analysis showed that it is possible to establish a relatively good LR between EC and clay, and between EC and sand (R²>0.60), allowing us to convert EMCI into sand and clay content and generate sand and clay 3D maps down to 0.60 m depth.