Cladistic analysis of Chinese Soil Taxonomy

Abstract

This study attempts to revise the search for natural groups and soil properties in Chinese soils based on the ideas of biological classification and soil genesis. Previous attempts at natural soil classification include the former Russian genetic soil classification, which classifies soils mainly based on soil forming factors. These attempts had resulted in classifications not ideally suited to soil identification. The US Soil Taxonomy (ST), however, has moved away from natural classifications and towards a robust key-based classification to identify soil Orders and groups. The current Chinese Soil Taxonomy (CST) system follows the ST. However, it remains unknown if the CST contains part of a natural classification (i.e. homologous properties or monophyletic groups). In this study, cladistics analysis was used to assess the 14 soil Orders and 39 Suborders of the CST using 44 morphological and numeric soil properties. Results show that it consists of a number of non-monophyletic groups. In order to test for monophyletic (i.e., natural) soil properties, all the non-homologous properties (e.g., moisture regimes, Mollic epipedon, Hydragric horizon) and numerical properties (e.g., n value and base saturation), were removed. The results indicated, Spodosols, Andosols, Gleyosols and Isohumosols Orders and Udic Vertosols and Anthric Primosols Suborders were more closely related to each other and may suggest a potential Superorder of mountainous and humid soils. Similarly, closely related Aridisols and Cambosols may indicate a potential Superorder of arid soils. However, some non-monophyletic Orders (e.g., Vertosols, Primosols) need revising based on their parent materials. Several aphyletic Orders (e.g., Anthrosols, Ferrosols, and Halosols) were identified due to insufficient information, which suggests additional morphological properties (e.g. pH) or other soil forming factors should be considered. We conclude that cladistic analysis can be also applied to extract information from the Russian soil classification, the ST and the World Reference Base to provide guidance for establishing a world-wide natural soil classification scheme.