Pedogenic properties of white clay soils of the Three River Plain, Heilongj iang Province, P.R. China

Abstract White clay soils are widely distributed in the Heilongjiang Province, P.R. China and are of agricultural importance in the province. However, there is only limited information available on the characteristics and pedogenesis of these soils. Three representative pedons of white clay soils in the Three River Plain, Heilongjiang Province were selected to determine physical, morphological, chemical and mineralogical properties and to relate these properties to the genesis and classification of these soils. Sr, Ti, and Zr were determined by X-ray fluorescence to establish parent material uniformity. Clay minerals were identified by X-ray diffraction methods. Micromorphology of the soils was based on petrographic examination of thin sections. Lithologic discontinuities were not detected based on the coefficients of variability associated with ratios of Zr Sr and Ti Zr within pedons. The profiles are characterized by a mollic epipedon, an albic E horizon and a thick argillic horizon. Physical, morphological, chemical and mineralogical properties indicate that lessivage was a dominant pedogenic process. Pedogenic FeMn nodules occur in Ah and E horizons. Maximum contents of pyrophosphate-extractable Fe and Al and oxalate- and dithionite-extractable Al occur in Bt2 horizons. The soils have relatively uniform pH values of about 4.5–5.0. Soil-vermiculite, which had not previously been recognized, is common in the clay fraction. The clay mineral assemblage is qualitatively similar throughout profiles. Continuous addition of aerosolic dust rich in mica and lessivage contributed to the quantitative variation in clay minerals within the pedon. The white clay soils are classified as Mollic Planosols in the FAO-Unesco System and Typic Argialbolls in Soil Taxonomy.