Field Determination of Soil Moisture in the Root Zone by Multi-height EM38 Measurements

Multi-height RigSoil Horizons

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Electromagnetic induction sensors, such as EM38, are used widely for monitoring and mapping soil attributes via the apparent electrical conductivity (ECa) of the soil. The sensor response is the depth-integrated combination of the depth-response function of the EM38 and 'local' electrical conductivity (ECa(z)) at depth. In deep Vertosols, assuming the depth-response function is not perturbed by the soil and where volumetric moisture content at depth (VMC(z)) dominates ECa(z), EM38 should be capable of predicting VMC(z). A multi-height EM38 experiment conducted over deep Vertosols confirmed the validity of the EM38 depth-response function. A simple model, involving mathematical summation of measured VMC(z) from sectioned 'calibration cores' and the known depth-response function of the EM38 was found to explain 87% and 83% of the variance in measured ECa for both horizontal and vertical dipole configurations respectively. This included all data acquired at multiple sensor heights above the ground.