Comparing soil taxonomy and WRB systems to classify soils with clay-enriched horizons (A case study: arid and semi-arid regions of Iran)

Document Type : Research Paper


1 Soil Science Department, Faculty of Agriculture, Vali-e-Asr University of Rafsanjan, Rafsanjan, Kerman, Iran

2 Soil and Water Research Institute (SWRI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran

3 Soil Science Department, Faculty of Agriculture, Shahid Bahonar, University of Kerman, Kerman, Iran


     Comparing the ability of ST and WRB systems to describe soils with clay-enriched horizons was the aim of the present research. In arid and semi-arid regions of Iran, two study sites were considered. Three pedons at each study site were selected, described and sampled. Soils were classified based on ST (2014) and WRB (2015) systems. The micro-morphological investigations were done to confirm the illuvial clay accumulation in Bt horizons. Results showed that the required characteristics of an argillic horizon were not met in any of the Bt horizons. The poor correlation between ST and WRB systems was related to the different definition and criteria of clay-enriched horizons in the systems. Using “Differentic” and “Cutanic” qualifiers, the WRB system could describe properties of an argic horizon more efficiently than the ST system. Although the evidence of clay illuviation was observed as lamellae in some argillic horizons in the arid study site, the ST system could not display this characteristic. The WRB system indicates the presence of lamellae using a “Lamellic” qualifier in some cases. These issues are disadvantages for both classification systems in describing the soils with clay-enriched horizons. Defining Natrisalids great group and new subgroups including Calcic Natrisalids, Lamellic Argigypsids and Lamellic Calciargids seems necessary to improve deficiencies of both classification systems. Adding the “Lamellic” qualifier for Calcisols in the WRB system is highly suggested.