Abstract:

Soil clayization discussed in the domestic and foreign literatures can be divided into three types: argillification, residual clayization and secondary clayification, but the formation of argic horizon, as a diagnostic horizon identified by luvisols, only involves argillification and secondary clayization. In mountainous and hilly areas of southern China, because of obvious soil desilication and aluminization, high soil Al³⁺ saturation, and high proportion of 1:1 type in clay minerals, it is difficult to have argillification in most cases. Secondary clayization generally occurs in the temperate regions with climatic conditions of semi-dry. Therefore, except for some soils derived from calcareous parent materials, there is no soil-forming environment of luvisols in mountainous and hilly areas of southern China. However, the difference of soil texture between surface and lower horizons in those areas is often the result of surface erosion in a long historical period. It is inconsistent with the principle of soil genesis and classification to classify those soils as luvisols. In order to avoid exaggerating distribution of luvisols in hilly and mountainous soils in southern China, and solve the uncertainties in the identification of both luvisols and cambosols, it is suggested that the definition of argic horizon in Keys to Chinese Soil Toxonomy should refer to the definition of argic horizon in USA Soil Taxonomy for taking base saturation (i.e. base saturation greater than 50%) as an index to identify argic horizon.

Key words: Luvisols, Clayization, Argic Horizon, Hilly and Mountainous Soils in Southern China