Characterization of clay minerals in white clay soils, People's Republic of China.
Xing B. | Dudas M.J.
The widely distributed white clay soils are major agricultural soils in China. While some of the chemical, physical, and morphological properties have been documented for these soils, there is little information available on their clay mineralogy. The purpose of this study was to conduct a detailed characterization of the clay mineralogy of white clay soils. Representative pedons were sampled by horizon and used in the detailed mineralogical study of these soils. Clay separates were analyzed by x-ray diffraction methods. Layer charge of 2:1 expandable phyllosilicates was determined by the n-alkylammonium ion exchange technique. Elemental composition of clay separates was determined by inductively coupled plasma atomic emission spectrometry. Vermiculite and smectites, which have not been recognized before, were identified in these soils. Other phyllosilicates were mica, kaolinite, and chloritic intergrades. Vermiculite had a uniform charge distribution of 0.82 mol(c)/O10(OH)2. Layer charge of smectites ranged from 0.36 to 0.47 mol(c) [O10(OH)2]-1 with a mean of 0.41 mol(c) [O19(OH)2]-1. Content of vermiculite in clay fractions ranged from 150 to 230 g kg-1, mica from 180 to 250 g kg-1, and kaolinite from 310 to 370 g kg-1. The high contents of kaolinite and mica in A and E horizons may be caused by aerosolic dust input and lessivage. Chloritic intergrades are thought to form from progressive filling of interlayer space of expanding phyllosilicates during pedogenesis. Smectites may have been derived from pedogenic weathering of vermiculite in these soils. Systematic documentation on clay mineralogy of white clay soils provides fundamental information for agricultural use and management of these soils.
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