Characterization of clay minerals of major upland soils in northeastern part of China

Northeastern part of China (Liaoning, Jilin and Heilongjiang provinces) ranges between 38:40-53:30 N and between 115:40-135:20 E. Geographically, the northeastern part of China is surrounded by mountains in the eastern, northern and western borders, and the plain distributed in the central and southern parts. Climate is characterized by the temperate to cool-temperate monsoon with the mean annual temperature of 0 to 8 degree C and the mean annual precipitation of 300 to 700 mm. The aim of the present study is to elucidate the clay mineralogical characteristics of major upland soils in the northeastern part of China. For this purpose, soil samples were collected at 12 sites covering Saline soils, Sols lessives, Meadow soils, Black-colored soils and Dark-brown forest soils which occupy more than 80 % of the upland field in the northeastern part of China. The particle-size distribution varied with sampling sites and with the horizons, reflecting the sedimentary nature of the parent material. In general, the clay content decreased in the order of Black-colored soils = Dark-brown forest soils Meadow soils, Sols lessives Saline soils. The sequence of the clay content among the soil types was generally similar to the results reported in China. Mineralogical composition of the clay fraction was examined by X-ray diffraction using the parallel powder mount. Predominant minerals identified were mica and 2 : 1 mixed-layer minerals, followed by vermiculite, kaolinite, quartz and feldspars. Chlorite and 2 : 1 minerals-chlorite intergrade were not detected. The similar mineralogical suite in the clay fraction irrespective of soil types indicates that the upland soils in the northeastern part of China are extensively affected by the eolian dust originating from the inland of China and Mongolia. 2 : 1 mixed-layer minerals are minerals which show the reflection around 18 A in the Mg-saturated and glycerol-solvated specimen. They could be grouped into the three groups depending on the line profile around 18 A. Type A is the mineral which shows the peak at 18 A with a slight tailing toward the lower angle and was designated as smectite with a small amount of mica as the mixed-layer mineral. Type B is the mineral which shows the shoulder around 18 A and was designated as the mica-smectite mixed-layer mineral. Type C is the mineral which hardly shows any peak or shoulder around 18 A and was designated as the mica-vermiculite-smectite mixed-layer mineral. Based on the correlation with cation exchange capacity, the inherent potentiality of upland soils in the northeastern part of China was estimated to by controlled by the clay content and then by the content and type of 2 : 1 mixed-layer minerals