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Attribution of Typical Aridisols and Halosols of Xinjiang Uygur Autonomous Region in Soil Taxonomy
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Abstract:
[Objective] To have the soils in Xinjiang (short for the Xinjiang Uygur Autonomous Region of China) reasonably, clearly and scientifically classified will lay down a good foundation for development, utilization, mapping and management of the soil resources in the arid regions of China. In the process of the research, contradictions are found in the Chinese Soil Taxonomy (3rd ed.). The definition of the Aridic epipedon in the CST states that "from the soil surface, there is no salt or sodic vesicular layer or a mixture layer of soil and salt underlying it", however, this definition does not specify depth of the specific underlay. In addition, according to this definition, the surface or the underlying soil layer without "saltilizing" is excluded. At the same time, the Sali-Orthic Aridosols is defined as " Salic horizon, Hypersalic horizon or Salipan with upper boundary within 100 cm of the mineral soil surface", which is obviously contradictory to the previous one, thus leading to classifying some of the soils containing Salic horizon into Aridisols. Moreover, under Calci-Orthic Aridosols, no Subgroup is set specifically for salt accumulation. Hence, even though some soil profiles do have Aridic epipedon, Calcic horizon and Salic horizon, their characteristics of salt accumulation are not reflected in their names as a type of soil. Therefore, it is necessary to study these contradictions for solution.[Method] In this paper, 17 typical Aridisols and Halosols soil profiles of Xinjiang were selected as objects for the study. Based on analyses of their morphological properties and physicochemical properties, the 17 soil profiles were sorted in attribution in CST. And as to the above contradictions, the following suggestions were put forth. The definition relevant to Aridic epipedon should be modified to:Down from the soil surface, no salt vesicular layer or sodic vesicular layer or underlying soil and salt mixture layer (not in compliance with the salt horizon condition). The definition of Sali-Orthic Aridosols should be modified to:Other Orthic Aridosols that contain a Salic horizon, a Hypersalic horizon or a Salipan with its upper boundary varying in the range of 30 cm to 100 cm in depth. And in addition, a Subgroup named Salic Calci-Orthic Aridosols should be augmented. Then classification of the 17 soil profiles was performed according to the proposed revisions, and Profiles No.1~No.11 were used as references between WRB, ST and CST.[Result] Classification in light of CST shows that of the 17 soil profiles, 15 profiles are of Aridisols and 2 profiles of Halosols. However, nine of the soil profiles (No.1, 4, 5, 9, 12, 14, 15, 16 and 17) are found to have a Salic horizon within 30 cm in depth, and hence they do not comply with the proposed definition of Aridic epipedon in CST, and should be shifted from Aridisols to Halosols in classification. Profile No.2 has an Aridic epipedon and a Calcic horizon, and a Salic horizon, too, down below 30cm in depth, but was named as Salic Calci-Orthic Aridosols. References between WRB, ST and CST show that Profiles No.1~No.11 are all in the order of Aridisols in light of ST and 10 in the order of Solonchaks and one in the order of Solonetz in light of WRB.[Conclusion] The contradictions in CST has expanded the area of Aridisols and reduced that of Halosols, which is not conducive to the amelioration and exploitation of Halosols. In this paper, the suggestions are put forward for revision of certain definitions to settle the contradictions in CST, such definitions of Aridic epipedon and Sali-Orthic Aridosols, and for augmentation of a Subgroup. "Salic Calci-Orthic Aridosols". According to the proposed revisions, among the 17 soil profiles, the number of Aridisols reduced from 15 to 6, and the number of Halosols increased from 2 to 11, and one soil profile was renamed as "Salic Calci-Orthic Aridosols", a newly augmented suborder as proposed. In this paper, only the typical Aridisols and Halosols in Xinjiang are taken as examples for the preliminary study. The next step is to expand the study area to have Aridisols and Halosols in other arid areas covered, for comparative analysis so as further perfect the Chinese Soil Taxonomy.
Keywords:
Project Supported:
Special Project of National Science and Technology Basic Research（2014FY110200A03）
Clc Number:
S155.3
