Characterization of tillage effects on the spatial variation of soil properties using ground-penetrating radar and electromagnetic induction

Tillage practices influence physical, chemical and biological soil properties, which also affect soil quality and consequently plant growth. In this study, the main objective was to evaluate the effects of different tillage practices on soil physical properties such as soil water content (SWC) by using geophysical methods, namely, ground-penetrating radar (GPR) and electromagnetic induction (EMI). Additional measurements such as soil sampling, capacitance probe, and soil penetrometer data were acquired as ground truths. The study was performed for three contrasting tillage practices, i.e., conventional tillage (CT), deep loosening tillage (DL), and reduced tillage (RT), applied on different plots of an agricultural field. The data showed that tillage influences soil resistance in shallow soil layers (deeper tillage decreases soil resistance), which could be partly seen in on-ground GPR data. In addition, reference SWC measurements (capacitance probes and soil sampling) were in fairly good agreement with the water content estimates from off-ground GPR. We also observed a tillage effect on shallow surface SWC, while deeper SWC seems to be unaffected by tillage. Mean surface SWC was significantly lower for CT compared to DL and RT, which was partly explained by lower pore connectivity between the topsoil and the deeper layers after conventional tillage. Moreover, the variance of the SWC within the conventional tillage plots was larger than within the other plots. This larger SWC variability could be explained by a greater soil heterogeneity induced by the plowing process. Overall, this study confirms the potential of GPR and EMI for the determination of soil physical properties at the field scale and for the assessment of agricultural management practices.