Properties of soils from the Swedish long-term fertility experiments. VI. Mapping soil electrical conductivity with different geophysical methods.
Swedish long-term soil fertility experiments were used to investigate the effect of texture and fertilization regime on soil electrical conductivity. In one geophysical approach, fields were mapped to characterize the horizontal variability in apparent
electrical conductivity down to 1.5 m soil depth using an electromagnetic induction meter (EM38 device). The data
obtained were geo-referenced by dGPS. The other approach consisted of measuring the vertical variability in electrical conductivity along transects using a multi-electrode apparatus for electrical resistivity tomography (GeoTom RES/IP device) down to 2 m depth. Geophysical field work was complemented by soil analyses. The results showed that despite 40 years of
different fertilization regimes, treatments had no significant effects on the apparent electrical conductivity. Instead, the comparison of sites revealed high and low conductivity soils, with gradual differences explained by soil texture. A significant, linear relationship found between apparent electrical conductivity and soil clay content explained 80% of the variability
measured. In terms of soil depth, both low and high electrical conductivity values were measured. Abrupt changes in
electrical conductivity within a field revealed the presence of ‘deviating areas’. Higher values corresponded well with layers with a high clay content, while local inclusions of coarse-textured materials caused a high variability in conductivity in some
fields. The geophysical methods tested provided useful information on the variability in soil texture at the experimental sites. The use of spatial EC variability as a co-variable in statistical analysis could be a complementary tool in the evaluation of
Lueck, E.; Ruehlmann, J.; Kirchmann, H. 2011. Properties of soils from the Swedish long-term fertility experiments. VI. Mapping soil electrical conductivity with different geophysical methods. Acta Agriculturae Scandinavica / B: Soil and Plant Science 61 (5), 438-447.