Digital soil mapping: case study from the Khouribga - Kasbat Tadla zone in Central Morocco

This work deals with the digital soil mapping as a time and cost effective alternative for soil type characterization. The e-Soter (Soil and terrain) approach was used and validated for in the Khouribga-Kasbat Tadla semi-arid rainfed agricultural area of Central Morocco, covering 217.000 ha. The GIS processing included physiography and parent material as two soil genesis factors, added to field data from 90 soil profiles. A subset of the ASTER-GDEM 30m spatial resolution digital elevation model (DEM) was used to map three physiographic indicators that are slope gradient, relief index and potential drainage density. The parent material classification was derived from 1/100.000 geological map. The e-Soter hierarchical classification was then used to derive e-Soter homogenous units that were spatially joined to soil profile data in order to define the most representative soil type and delineate soil homogenous units at the 100.000 scale. The resulting soil map was validated in the field using a transect approach, with three transects in areas that were not included in the initial field data collection. Statistical significance for similarity between the map outputs and the field observations was confirmed using four statistical indices (Chi square, Cramér’s V, Fisher’s exact and Kappa reliability test), which confirms the validation of the e-Soter approach as a digital soil mapping tool in the study area.