Abstract
Aluminum extractability and solubility were investigated in detail in six horizons of a Typic Haplohumod (FAO: Haplic Podzol) from southern Switzerland. Pyrophosphate and oxalate extractions as well as successive acid leaching indicated that in the Ah, (AE), and Bh horizons reactive Al is mainly bound to soil organic matter, whereas in the Bs, BC1, and BC2 horizons it is of inorganic nature. In the latter three horizons, infrared (IR) spectroscopy and transmission electron microscopy (TEM) revealed the presence of imogolite. Batch equilibrium experiments at 20°C in the pH range of approximately 3.5 to 5.5 showed that the podzol profile can be divided into two parts of different Al solubility control. In the Ah and (AE) horizons, Al solubility was found to be controlled by complexation reactions to soil organic matter. Kinetic studies with samples of the Bh, Bs, BC1, and BC2 horizons showed that ion activity products with respect to both Al(OH)3 and imogolite, (HO)3Al2O3SiOH, reached a constant value after reaction times of 16 d. For pH >4.1, the compilation of all data revealed and These data could be shown to be consistent with either Al solubility control by imogolite‐type material (ITM) with a log , which dissolves incongruently, or a simultaneous equilibrium with ITM and hydroxy‐Al interlayers of clay minerals. For pH <4.1, data indicated solubility control by a 1:1 aluminosilicate, e.g., poorly crystalline kaolinite.
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