Soil substrate classification and the FAO and World Reference Base systems: examples from Yemen and Jordan

Abstract

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.

Archaeopedological analyses around a Neolithic hearth and the beginning of Sabaean irrigation in the oasis of Ma'rib (Ramlat as-Sab'atayn, Yemen)

“…Soil description follow FAO Guidelines (FAO, 2006), substrate classification was done after Pietsch and Lucke (2008). Particle size distribution of fine earth (<2 mm) was determined by sieving and analysing the <63-mm fractions by pipette using Na 4 P 2 O 7 as a dispersant.…”

Terrace soils in the Yemen Highlands: Using physical, chemical and radiometric data to assess their suitability for agriculture and their vulnerability to degradation

“…Because of high silt and clay contents, colour and the occurrence of detritus, the colluvial soil substrates can be defined as "brown cover loam on slope with few/common/many detritus". Only the base of Ir02 is built of "wadi sediments with many gravel" (after Pietsch and Lucke, 2008).…”

“…Soil colours were identified using Munsell Soil Color Charts (2000). Classification was carried out according to the World Reference Base for Soil Resources (WRB, IUSS-Working Group WRB, 2007), layer identification followed Ollier and Pain (1996), and substrate classification was done according to Pietsch and Lucke (2008). Since it is known that on a local scale physical and chemical properties of soils vary spatially (Johnson et al, 1990), bulk samples were collected from the middle of each horizon/layer, rather than taking samples of high-resolution depth increments from the whole profile.…”

Climate and relief influence on particle size distribution and chemical properties of Pseudogley soils in Croatia

“…According to the substrate classification of Pietsch and Lucke (2008), parent materials of Croatian Pseudogleys can be labeled as Pleistocene (qp) white-yellowish (w) cover loams (L). Although these parent materials are of aeolian genesis (e), post-depositional superficial denudative processes (df) were possible on slopes.…”