Application of EMI-Measured Magnetic Susceptibility to Characterise Soil Drainage Conditions Over Various Soil Types

Electromagnetic induction (EMI), by Geonics EM38, was used to characterise the volumetric magnetic susceptibility (MS) of soils on 12 farms in southwestern Ontario, Canada. Three different points on lower, middle and upper slope positions were selected at each farm to represent poorly-, moderate- and well-drained soil. Soil core samples were collected for each measurement point, from which soil redoximorphic conditions (gleying and mottling) were characterised at 5 cm depth increments. The volume MS, mass-specific MS and frequency dependence (FD) of MS of soil samples were carried out using Bartington MS2C and MS2B sensors, respectively. The impact of heating the samples to 400°C and 700°C on soil MS was also investigated. Results show that at each farm, the lowest volume MS values belong to soils at the lower slope position, which is poorly drained, and the highest volume MS values belong to the soils at the upper slope position, which is well drained. The inverted models from apparent MS data, measured by EM38, seem to be good representatives of volume MS readings attained from core samples. Results show that at most of the selected points, while the FD is higher in poorly drained points than in moderate and well-drained ones, the mass-specific MS shows an opposite behaviour, which can be used as attributes to characterise poorly and well-drained soil conditions.