Adequacy of soil information resulting from geopedology-based predictive soil mapping for assessing land degradation: case studies in Thailand

Soil is a natural body which delivers important ecosystem services apart from being a medium for plant growth. Soil mapping can be time consuming and expensive. During the 1960s and 1970s, introduction of air photo-interpretation in soil survey through element analysis, physiognomic and physiographic analysis, helped increase mapping efficiency. In the late 1980s, the geopedologic approach to soil mapping amplified the role of geomorphology. It helps understand soil variation in the landscape which increases mapping efficiency. In the present study, the adequacy of soil data resulting from geopedology-based predictive soil mapping for assessing land degradation in three locations in Thailand is assessed. The result shows that the geopedologic approach helps map soil in inaccessible mountain areas. However, for application in land degradation studies all the required soil properties may not be available in a soil map. The effect of land cover and land use management practices on soil properties, such as porosity and compaction having effect on hydraulic conductivity, a parameter used in modelling rainfall-runoff-soil erosion, is usually not reported in soil survey. These data have to be collected separately. For mapping areas susceptible to frequent flood, the geomorphic understanding of the river valley and soil characterization (Fluventic and Aquic) help identify susceptible areas. Similarly, the study shows how the geopedologic approach in combination with digital image processing helps in mapping soil salinity hazard.