Geophysical methods of soil fertility mapping for precision agriculture applications in semi-arid regions (Morocco)

Experiments on a plot-scale of apparent electrical conductivity (ECa) and resistivity (ERT) variation with correlation of soil properties were studied for soil mapping at the experimental farm of Mohammed VI Polytechnic University of Benguerir (UM6P). The ElectroMagnetic Induction (EMI) technique was applied using a soil sensor EM38-MK2 which provides auxiliary ECa data sets with accuracy. The other method ERT was used to measure the electrical resistivity. The study was supported by soil sampling to ensure the reliability and potential of ECa measurements for soil mapping.  ECa readings in mS/ m ranged from 12 to 26 and 8 to 20 respectively in the vertical (ECa-V) and horizontal mod. ECa and ERT readings correlated best with soil properties such as texture (clay and sand), and upper soil chemical properties (OM, CEC, Ca2+, Fe2+and Mg2+). A modest correlation was found between ECa-V, clay and subsurface water content (r = 0.80), (r = 0.79). The linear relationship found between apparent electrical conductivity and soil clay content explained 80% of the measured variability. The results of the study raised the hope that soil mapping by ECa measurement can fairly represent the spatial variation of soil properties such as texture, chemical fertility and organic matter content. The use of spatial variability in EC as a co-variate in statistical analysis could be a complementary tool in the evaluation of experimental results.