Mineralogy Characteristics Of Soil Evolution On The Loess Parent Materials Under Different Hydrothermal Conditions On The Loess Plateau

Iron oxides and clay minerals are derived from weathering of parent material and precipitated from the soil solution. They reflect successive stages of mineralogical evolution depending on the various environmental conditions that have prevailed during soil formation. This study focused on the mineralogy in12soil profiles of3types of vegetation types (grassland、bushwood and arbor) of Jingyuan country of Gansu province, Guyuan country of Ningxia province, Chongxin country of Gansu province, Baishui and Weinan country of Shanxi province from northwest to southeast in the Loess Platea to analyzed the distribution of soil iron oxides and its affecting factors, and combined with the clay mineral assemblages to revealed the pedogenesis change. The main results are as follows:1. The iron oxide content in the soil profile in different climatic zones of Loess Plateau were significantly different. The contents of the soil free iron oxide significantly risen up (P<0.01), and the contents of the amorphous iron obviously reduced (P<0.01) with the water and heat condition improved the soil development get better from northwest to southeast. The trend of the contents of the crystalline iron and the values of Feo/Fed ratio showed significant difference in different climatic zones.2. The content of soil organic、CaCO3and pH have significant effect on the free iron oxide. The content of soil organic is negatively related (P<0.01) to free iron oxide and positively related (P<0.01) to the amount of noncrystalline iron oxides; the content of CaCO3and pH are negatively related (P<0.01) to noncrystalline iron oxides. The accumulation of soil organic contributes to forming and preserving noncrystalline iron oxides, the increasing of carbonate and Alkalinity of soils are not avail to forming iron oxides. The vegetation types has very significant (P<0.01) effect on the content of iron oxides, The distribution of free iron oxide content in different vegetation types tend to be in the order of grassland (16.21g/kg)> bushwood (15.45g/kg)> arbor (15.38g/kg), While about the noncrystalline iron oxides in the order of bushwood (1.43g/kg)> grassland (1.38g/kg)> arbor (1.08 g/kg). The vegetation types indirect effect the content of iron oxides by effecting the content of soil organic and water.3. Mineralogical compositions of the soil profile in different climatic zones of Loess Plateau is found to be similar with the illite in the majority, Vermiculite%Kaolinite and Chlorite take second place and few Montmorillonite, Baishui and Weinan country of Shanxi province contains no Chlorite; There were significant difference in the relative content of clay mineral, the relative content of Montmorillonite is almost constant, the Illite、Chlorite reduce evidently (P<0.05) and Kaolinite and Vermiculite increase significantly (P<0.01) from northwest to southeast. This indicates climate transformed into warmer and wetter, and chemical weathering was gradually strengthened from northwesttosoutheast.4. The clay minerals structural characteristics index changed significantly with the variations of climate zone, the values of HHW、ICI and I/C raised gradually with the climate conditions improving that indicates pedogenesis environments transformed into warmer and wetter; The clay minerals Microstructure microstructure showed trioctahedral peak intensity reduced gradually while peak intensity dioctahedron increased gradually with the change of climate zone, the results show that with the improving of hydrothermal condition soil weathering process and the degrees of soil development enhanced.