Vertisols and Vertic Soils in Arid and Semiarid Climate Regions in China.

Studies indicate that Torrerts and vertic soils are observed in areas with mid-temperate and warm temperate monsoonal arid or semiarid climate mainly in Inner Mongolia, Ningxia and Xinjiang Autonomous Regions. The mean annual precipitation in these locations is between 365mm and 100mm  from east to west. The potential evaporation rate is very high. The soil moisture regime is aridic.

The Torrerts and vertic soils are derived from weathered, or residual deposit of argillaceous rocks in the Cretaceous, Jurassic and Neogene period, of Quaternary basalt, as well as N2 red-clayey palaeosols. Their water transported sediments are agricultural land. The soil clay content (<0.002mm) is between 35.40 and 56.49%. The expansive potential of the Vertisols is high. Angular blocky/wedged-shaped structure, or slickenside, as well as cracks are present. The cracks remain open, but close for less than 60 consecutive days as soil water content increases through rainfall in summer. The Torrerts inherit the expandable clay minerals ,such as montmorilllonite and illite- montmorilllonite from parent materials. This is similar to the Vertisols that were identified in the eastern and southern part of China.

The Vertisols may also exist in the Xizang Plateau (Tibet), such as in North Xizang, where the climate is classified as, Plateau temperate arid. The annual precipitation is only 75mm concentrating in summer. Parent material is mainly old lacustrine. The soil clay content (< 2µm) is as high as 75%, with cracks 1 cm in width. Salts accumulate on the land surface. Further investigation is needed in that particular region.

The thickness of soil horizon of some Torrerts is more shallow than other suborders of Vertisols in eastern and southern China. But the soils and underlying expansive soft rocks have damaged various constructions in NW China and Inner Monogolia China. Many methods have been used to combat the hazards.

This research provides information for improving the Chinese Soil Taxonomy. Only three suborders of Vertisols were recognized in the edition in 2001.