The Use of Electromagnetic Induction to Monitor Changes in Soil Moisture Profiles beneath Different Wheat Genotypes

Abstract

There has been recent interest in the use of surface deployed geophysical methods to estimate soil moisture profiles. In this study we applied multi-coil, frequency domain, electromagnetic induction (EMI) geophysical surveys to determine electrical conductivity (σ) profiles of the root zone of four winter wheat (Triticum aestivum) genotypes, grown in randomized block experiment with four replicates. Field measurements of apparent electrical conductivity (σa) were obtained at sites with two different soil textures. We used the cumulative sensitivity model to predict EMI conductivity data from the conductivity profile measured with electrical resistivity tomography (ERT) on a subset of the plots we investigated. During the inversion of the EMI data, conductivities were adjusted on all plots so that they were consistent with ERT data. Changes in electrical conductivity of field soil, with depth computed from inversion of EMI data, over the growth period were compared with measured changes in soil water content. Laboratory measurements confirmed a positive correlation between electrical conductivity and soil water content. Between crop emergence and maturity water extraction by the different wheat genotypes reduced water content by up to 30 percent. Comparing changes in electrical conductivity between reference profiles determined shortly after crop emergence, with electrical conductivity profiles at later dates as the crop matured, we were able to use EMI to remotely monitor moisture extraction by the roots of different wheat genotypes, with depth and over time.