干旱区生态环境知识资源中心

The World Reference Base for Soil Resources and the FAO Guidelines for Soil Description are tools to identify, describe and classify a soil by diagnostic horizons, diagnostic properties, diagnostic materials, and other soil features. While bedrock and residual fragments can be defined by their lithology and abundance, the parent material of soil formation is not clearly classified. Therefore a substrate classification was implicated in descriptions of layered soils, because these consist often of allochthonous, polygenetic and heterogeneous substrates. Results of soil investigations in Yemen developed into a substrate classification key for parent materials that focuses on parameters of substrate variety. Primarily, the present approach was developed to describe layered soils on the Island of Socotra, but it is assumed to be valid for any semi-arid region in the Tropics and Subtropics. To assess the operational reliability of the system, it was applied to classify parent materials of soils from Yemen mainland and Jordan. The classification key is partly based on the FAO Guidelines, and partly on the German Soil Mapping Guidelines. The substrate variety includes lithology, weathering intensity, stratigraphical unit and substrate form. Different substrate varieties within one profile are called substrate orders and closely relate to sedimentary bedding. The proposed classification key is based additionally on parameters such as geogenesis and relief position. It can be used separately from soil description. However, soil identification and description become more precise by using this classification system. This contribution should be understood as a first approach to an international substrate classification.