Mineralogy of B horizons in alpine forest soils of Taiwan

The nature of minerals in the B horizons of alpine forest soils in subtropi cal and tropical areas remains to be identified. The objective of this stud y was to investigate the distribution of Fe-oxides and hydroxy-interlayered vermiculite (HIV) in typical alpine forest soils of Taiwan, Five pedons at roughly 2000 m elevation of Taiwan were selected as example for this study. High gradient magnetic separation (HGMS), conventional X-ra y diffraction (XRD), differential X-ray diffraction (DXRD), and transmissio n electron microscopy (TEM) were employed to characterize the clay minerals . The content of crystalline Fe-oxides increased sharply from E to B horizo ns. Only Al-substituted lepidocrocite and goethite were identified by diffe rential X-ray diffraction (DXRD) analysis in magnetic clay fractions of the B (or placic) horizons; no substantial hematite peaks appeared in the XRD patterns of any pedons, These observations are quite different from those o f Spodosols or Spodosol-like soils developed in the temperate and frigid zo nes of North America, Hydroxy-interlayered vermiculite (HIV) was characteri zed by collapse of the 1.42-nm peak in the XRD diagrams toward 1.0 nm when the K-saturated clay samples were heated to 350 degrees C. In the surface h orizons, only vermiculite could be identified in the coarse clay fractions. The distribution patterns of acid ammonium oxalate extractable Fe and Al i n these pedons indicate that Al and Fe were leached from the A horizons and accumulated in the B horizons when forming Al-substituted lepidocrocite, g oethite, and HIV, This is attributed to the combined effect of organic acid s, Al, and Fe in the pedogenic environments. The present findings are of fu ndamental significance in understanding the formation of Spodosol-like soil s in alpine forest soils in the subtropics and tropics.